Preconditioning preserves energy metabolism in prolonged low-flow ischemia

Background: A reduction in coronary flow leads to a parallel decrease in contractile function. Thus, a flow/function balance is established in the myocardium under certain circumstances avoiding the development of a necrosis (referred to as “hibernating” myocardium). The impact of a preconditioning period on this critical balance was examined. Methods: In 116 isovolumetrically beating rat hearts, 3 h of hypoperfusion with 15% of control coronary flow were performed followed by 1 h reperfusion; 40 hearts served as controls. As a preconditioning period, in half of the rat hearts a 5 min no-flow ischemia followed by 10 min reperfusion was performed, preceding the prolonged hypoperfusion. Results: Systolic function was identically reduced in both groups after 3 h hypoperfusion (LVP: 39±2 mmHg, 40±2 mmHg vs. controls 90±3 mmHg; p<0.01). Without preconditioning hypoperfusion resulted in a marked initial decrease in function. This period was followed by an adaptation to a higher steady state level of function compared with non-preconditioned hyperperfused hearts (p<0.05). After preconditioning hypoperfusion directly resulted in this level of contraction. Contractile reserve was reduced (p<0.01) identically in both hypoperfusion groups. Adenine nucleotides were decreased (p<0.01) after 3 h hypoperfusion to 2.1±0.2 μmol/gww vs. controls (4.7±0.2 μmol/gww). After initial preconditioning adenine nucleotides were better preserved (3.2±0.2 μmol/gww) going ahead with a creatine phosphate overshoot of 126% (p<0.01). After reperfusion, systolic function and contractile reserve were identical in both groups. Conclusion: A period of preceding no-flow ischemia followed by reperfusion modifies functional adaptation to hypoperfusion and preserves high energy phosphates. Therefore, the metabolic balance during hypoperfusion is improved by preconditioning, although no impact on contractile reserve or the functional status of reperfused myocardium after low-flow ischemia can be seen. Received: 12 March 1998, Returned for 1. revision: 25 March 1998, 1. Revision received: 12 May 1998, Returned for 2. revision: 2 June 1998, 2. Revision received: 13 July 1998, Accepted: 21 July 1998     

The influence of maturation and gender on the anti-arrhythnmic effect of ischaemic preconditioning in rats

The aim of this study was to investigate the influence of maturation and gender on the anti-arrhythmic effect of myocardial ischaemic preconditioning in rats. Coronary artery occlusion was carried out in either rats anaesthetised with sodium pentobarbitone or in rat isolated hearts. Cardiac arrhythmias occurring in the 30 min post-occlusion period were assessed. In anaesthetised 3 month (m) old male rats ischaemic preconditioning, with a 3 min temporary coronary artery occlusion, significantly reduced the total number of ventricular ectopic beats (VEBs) from 2074±206 to 490±139 and the incidence of ventricular fibrillation (VF) from 40 to 0% during a subsequent 30 min occlusion (P<0.05). In middle-aged male rats (16 m) the anti-arrhythmic effect of preconditioning was unaltered (VEBs were reduced from 1958±121 to 245±66 and VF from 70 to 0%). In 3 m old anaesthetised female rats the effect of ischaemic preconditioning was also evident (VEBs reduced from 961±170 to 154±48; P<0.05). In non-preconditioned age-matched female animals the total number of VEBs (961±170), VF (0%) and mortality (0%) were significantly (P<0.05) lower than in respective male animals. In female rats, attenuation of ischaemia-induced arrhythmic severity was most pronounced in the oestrus state. In hearts isolated from weight-matched male and female rats the incidence of ventricular tachycardia (81 vs 25%) and the total number of VEBs (351±73 vs 81±50) were significantly (P<0.05) different. It is concluded that in rats neither maturation nor gender influence the anti-arrhythmic effect of ischaemic preconditioning. However, female rats exhibit a lower level of arrhythmic activity during sustained coronary artery occlusion than male rats both in vivo and in vitro. Received: 8 April 1998, Returned for revision: 2 June 1998, Revision received: 9 July 1998, Accepted: 21 July 1998     

Ventricular arrhythmias following coronary artery occlusion in rats: is the diabetic heart less or more sensitive to ischaemia?

Rhythm disorders are common complications in diabetic patients, due to their enhanced sensitivity to ischaemia. However, experimental studies are inconsistent, and both higher and lower vulnerability to injury has been reported. Our objectives were to compare susceptibility to ventricular arrhythmias in rats with prolonged duration of diabetes induced hy streptozotocin (45 mg/kg, i. v.), utilising two different models. Following 8 weeks, either anaestetised open-chest rats in vivo or isolated Langendorff-perfused hearts were subjected to 30 min regional zero-flow ischaemia induced by occlusion of LAD coronary artery. In addition, cardiac glycogenolysis and lactate production were measured. In open-chest rats, 90% of the controls exhibited ventricular tachycardia (VT) which represented 55.4% of total arrhythmias, whereby only 19.9% of arrhythmias occurred as VT in 44% of the diabetic rats (P < 0.05 vs controls). Duration of VT and ventricular fibrillation (VF) was reduced from 35.5 ± 11.1 and 224.8 ± 153.9 s in the controls to 4.8 ± 2.5 and 2.2 ± 0.2 s in the diabetics, respectively (P < 0.05). Accordingly, severity of arrhythmias (arrhythmia score, AS) was also lower in the diabetics (2.0 ± 0.38 vs 3.3 ± 0.3 in the controls; P < 0.05). In the isolated hearts, high incidence of VF was decreased in the diabetic hearts, and although VT occurred in almost all of the diabetic hearts, the duration of VT and VF was substantially shorter (61.5 ± 14.5 and 5.5 ± 0.5 s vs 221.5 ± 37 and 398.5 ± 55 s in the controls, respectively; P < 0.05). AS was reduced to 2.9 ± 0.12 from 4.1 ± 0.3 in the controls (P < 0.05). Postischaemic accumulation of lactate was lower in the diabetic than in the non-diabetic myocardium (20.4 ± 1.9 vs 29.5 ± 2.9 μmol/l/g w.wt.; P < 0.05). These results suggest that rat hearts with chronic diabetes, despite some differences in the arrhythmia profiles between the in vivo model and isolated heart preparation, are less sensitive to ischaemic injury and exhibit lower susceptibility to ventricular arrhythmias and reduced accumulation of glycolytic metabolites. Received: 3 April 2000, Returned for 1. revision: 9 May 2000, 1. Revision received: 5 July 2000, Returned for 2. revision: 7 August 2000, 2. Revison received: 11 September 2000, Returned for 3. revision: 27 September 2000, 3. Revision received: 13 October 2000, Accepted: 16 October 2000     

Effect of the platelet-activating factor antagonist RP 59227 (Tulopafant) on myocardial ischemia/reperfusion injury and neutrophil function

The effect of the platelet activating factor antagonist RP 59227 (Tulopafant) on myocardial infarct size was compared to that of vehicle-treated control group in barbital-anesthetized dogs subjected to 90 min of left circumflex coronary artery occlusion and 5 h of reperfusion. The myocardial region at risk and infarct size were determined by the triphenyltetrazolium histochemical technique and regional myocardial blood flow by radioactive microspheres. Myeloperoxidase (MPO) activity was used as an index of neutrophil infiltration into the ischemic-reperfused area. Vehicle (n=11) or RP 59227 (n=12, 2.5 mg/kg i.v.) were administered 15 min prior to occlusion. Hemodynamics and regional myocardial blood flow in the ischemic-reperfused areas did not differ between the two groups throughout the experiment. In contrast, the number of dogs which developed ventricular fibrillation during occlusion and reperfusion was significantly less in RP 59227-treated dogs (8 of 11 in the control group vs. 3 of 12 in the RP 59227-treated group, p<0.05). Myocardial infarct size expressed as a percent of the area at risk (control, 39.0±5.0; RP 59227, 24.8±3.4%) or as a percent of the left ventricle (control, 15.3±1.9; RP 59227, 9.0±1.3%) was significantly smaller in the RP 59227-treated group. Infarct size was inversely related to the collateral blood flow in the inner two thirds of the left ventricular wall of the infarct area, and this relationship was shifted downward in the RP 59227-treated group (p<0.05). MPO activity in the border zone immediately adjacent to infarcted tissue was reduced in the RP 59227-treated dogs (control, 7.4±0.5 U/g; RP 59227, 4.1±0.4 U/g). In additional in vitro studies, the addition of PAF was found to elicit a concentration-dependent potentiation in chemiluminescence produced by purified canine neutrophils, a measure of oxygen-derived free radicals, which was stimulated with a low concentration of opsonized zymosan. Preincubation of neutrophils with RP 59227 resulted in a concentration-dependent decrease in chemiluminescence produced by PAF primed cells. Taken together, these data demonstrate that RP 59227 effectively reduces myocardial infarct size and reduces the incidence of ischemia and reperfusion-induced arrhythmias in barbital-anesthetized dogs, and support the concept that PAF plays an important role in the pathogenesis of acute myocardial infarction. Received: 11 March 1998, Returned for 1. revision: 2 April 1998, 1. Revision received: 18 May 1998, Accepted: 18 May 1998     

Skeletal muscle abnormalities in rats with experimentally induced heart hypertrophy and failure

Background: In congestive heart failure (CHF), function and metabolism of skeletal muscles are abnormal. Aim: To evaluate whether the reduced oxidative capacity of skeletal muscles in CHF is due to impaired O₂ utilisation. Methods: CHF was induced in rats by injecting 50 mg/Kg monocrotaline. Several animals received the same dose of monocrotaline but only compensated right ventricular hypertrophy and no sign of congestion resulted. Two age- and diet-matched groups of control animals were also studied. In soleus and extensor digitorum longus (EDL) muscles, we studied skeletal muscle blood flow, oxidative capacity and respiratory function of skinned muscle fibres. Results: In CHF, we observed a decrease of muscle blood flow (statistically significant in the soleus, p < 0.05 vs. controls). In compensated rats, a similar trend in blood flow was observed. In both soleus and EDL, a significant reduction of high energy phosphate and a shift of the redox potential towards accumulation of reducing equivalents were observed. The reduction of energy charge was not correlated to the decrease of blood flow. In skinned myofibres, the ratio of O₂ utilised in the presence and in absence of ADP (an index of phoshorilating efficiency) was reduced from 8.9 ± 1.9 to 2.7 ± 0.2 (p < 0.001) and from 5.7 ± 1.0 to 2.0 ± 0.3 (p < 0.01) in soleus and EDL, respectively. Activity of the different complexes of respiratory chain was investigated by means of specific inhibitors, showing major abnormalities at the level of complex I. In fact, inhibition of VO₂ by rotenone was decreased from 83.5 ± 3.2 to 36.4 ± 9.6 % (p < 0.005) and from 81.8 ± 6.1 to 38.2 ± 7.4 % (p < 0.005) in soleus and EDL, respectively. Conclusions: In rats with CHF, abnormalities of oxidative phosphorylation of muscles occur and complex I of the respiratory chain seem to be primarily affected. The metabolic alterations of skeletal muscles in CHF may be explained, at least in part, by an impaired O₂ utilisation. Received: 22 February 2002, Returned for 1. revision: 14 March 2002, 1. Revision received: 5 June 2002, Returned for 2. revision: 21 June 2002, 2. Revision received: 23 August 2002, Accepted: 12 September 2002 Correspondence to: Dr. C. Ceconi     

Phase angle convergence of multiple monophasic action potential reordings precedes spontaneous termination of ventricular fibrillation

Aims To elucidate the mechanism of spontaneous termination of ventricular fibrillation (VF) and to define an indicator of its occurrence, the phase angle, a novel measure to assess synchrony of activation, was evaluated. Methods and results In 7 isolated rabbit hearts, 7 monophasic action potentials were recorded simultaneously. Ventricular fibrillation was induced by T wave shocks. Cycle lengths (CL) and phase angles between all 7 recordings were analyzed until spontaneous termination or shock-induced defibrillation. Average phase angle was calculated as activation time difference to a reference channel and expressed as a fraction of the reference channel's CL with 1 equaling a complete CL. Initial CLs and phase angles were similar in sustained and terminating episodes (CL: 141±16 ms vs 142±24 ms, phase angle: 0.244±0.11 vs 0.263±0.1, p=NS). During spontaneous termination, CL increased slightly by 7%. Average phase angle converged gradually over the last three activations before termination of ventricular fibrillation by 22–48% (p<0.0005), eventually resulting in phase angles similar to paced rhythms directly prior to spontaneous termination of ventricular fibrillation. Conclusions Gradual synchronization of activation is part of the electrophysiological mechanism resulting in spontaneous ventricular fibrillation termination and can be detected three activations before termination. Phase angle convergence may be useful to detect spontaneous termination of ventricular fibrillation. Received: 24 October 1997, Returned for 1. revision: 24 November 1997, 1. Revision received: 21 January 1998, Returned for 2. revision: 4 March 1998, 2. Revision received: 29 April 1998, Returned for 3. revision: 25 May 1998, 3. Revision received: 15 June 1998, Accepted: 17 June 1998     

Angiogenesis and microvascularization after cryothermia-induced myocardial infarction: A quantitative fluorescence microscopic study in rats

Microvascularization of infarcted myocardial tissue may be a prerequisite for successful therapeutic interventions, including cardiomyoblast or satellite cell transplantation. Because little is known on microvascular restitution within infarcted tissue, we studied angiogenesis and microvascularization after cryothermia-induced myocardial infarction using intravital fluorescence microscopic techniques. Methods: In anesthetized, orally intubated and ventilated Sprague-Dawley rats (n = 20), a sternotomy was performed and a standardized cryolesion was induced to the right ventricle by freezing for 5 min to −160°C. Myocardial angiogenesis and microvascularization were analyzed quantitatively after rethoracotomy on days 7 (n = 6) or 28 (n = 8). Sham-operated animals (n = 6) served as controls. Results: Seven days after cryothermia, the central tissue area of the injured myocardium (28.4 ± 9.2 mm²) was characterized by complete lack of capillary perfusion, while the periphery of the cryolesion (27.6 ± 5.7 mm²) revealed a heterogeneous capillary perfusion pattern with a density of 300.9 ± 38.9 cm⁻¹. Adjacent myocardial tissue showed intact capillary perfusion (density: 563.0 ± 44.4 cm⁻¹) comparable with that of sham-operated controls. After 28 d the area with lack of capillary perfusion was found significantly reduced to 7.3 ± 3.7 mm² (P < 0.05); however, it was still surrounded by a heterogeneously perfused area of myocardial tissue of 57.7 ± 19.2 mm² (density: 271.1 ± 52.7 cm⁻¹), indicating partial restitution of capillary perfusion. Although at day 7 within the central zone of the cryolesions, capillary perfusion was completely shut down, perfusion of microvessels larger than capillaries, i.e., arterioles and venules, were found maintained, however, with a density markedly lower (1.96 ± 1.04 mm⁻¹) when compared with that of sham-controls (4.28 ± 1.52 mm⁻¹). After 28 d the number of these larger-sized microvessels increased significantly with values of density even higher compared with those observed in controls (6.89 ± 1.71 mm⁻¹, P < 0.05), indicating new vessel formation. Conclusions: Our study indicates partial restitution and function of the microvascular network within infarcted myocardial tissue, which may serve as an appropriate prerequisite for successful application of novel therapeutic strategies to improve myocardial function. Received: 6 May 1998, Returned for revision: 2 June 1998, Revision received: 9 November 1998, Accepted: 3 December 1998     

Effects of propafenone on anisotropic conduction properties within the three-dimensional structure of the canine ventricular wall

Background Structural complexities of the intact ventricular wall cause a very complex spread of activation. The effects of regional tissue damage and of antiarrhythmic drugs on directional differences in activation should help to further elucidate intramural conduction patterns. Methods and results In 10 healthy dogs and in 5 dogs with subacute anterior wall infarction, 6 parallel rows of 6 needle electrodes with 4 bipolar electrode pairs per needle were inserted into the left anterior ventricular wall. Using a computerized multiplexer-mapping system, the spread of activation in epi-, endo- and midmyocardial muscle layers and in the surviving epicardium, respectively, was reconstructed. Marked differences in conduction velocities relative to fiber orientation were evident in the surviving epicardium of infarcted hearts. Directional differences in conduction velocities, although less pronounced, were still preserved throughout the intact ventricular wall. Epicardial transverse conduction in intact hearts was significantly faster than transverse conduction in infarcted hearts (0.87 ± 0.11 m/s vs 0.68 ± 0.1 m/s). In normal hearts, propafenone (2 mg/kg) decreased conduction velocities primarily in longitudinal directions (−27 ± 10%), but also moderately in transverse directions (−13 ± 7%) of all muscle layers, with no significant effect on straight (−4 ± 8%), but on oblique transmural conduction (−33 ± 18%). In infarcted hearts propafenone decreased conduction particularly in longitudinal direction (−23 ± 14%) without affecting conduction transverse to the fiber orientation (+3 ± 6%). Conclusions Longitudinal intramural shortcircuits reduce directional differences in activation. Transmural infarction results in a loss of alternative intramural pathways, unmasking marked anisotrophy in the surviving epicardium. Conduction delay in intramural pathways explains the effects of propafenone on transverse and oblique transmural conduction. Primarily longitudinal conduction delay results in reduced tissue anisotropy. Received: 8 June 2000, Returned for revision: 4 July 2000, Revision received: 20 September 2000, Accepted: 9 October 2000     

Influence of mild hypothermia on myocardial contractility and circulatory function

Myocardial contractility depends on temperature. We investigated the influence of mild hypothermia (37–31°) on isometric twitch force, sarcoplasmic reticulum (SR) Ca²⁺-content and intracellular Ca²⁺-transients in ventricular muscle strips from human and porcine myocardium, and on in vivo hemodynamic parameters in pigs. In vitro experiments: muscle strips from 5 nonfailing human and 8 pig hearts. Electrical stimulation (1 Hz), simultaneous recording of isometric force and rapid cooling contractures (RCCs) as an indicator of SR Ca²⁺-content, or intracellular Ca²⁺-transients (aequorin method). In vivo experiments: 8 pigs were monitored with Millar-Tip (left ventricular) and Swan-Ganz catheter (pulmonary artery). Hemodynamics parameters were assessed at baseline conditions (37°), and after stepwise cooling on cardiopulmonary bypass to 35, 33, and 31°C. Hypothermia increase isometric twitch force significantly by 91 ± 16% in human and by 50 ± 9% in pig myocardium (31 vs. 37°C; p < 0.05, respectively). RCCs or aequorin light emission did not change significantly. In anesthetized pigs, mild hypothermia resulted in an increase in hemodynamic paramters of myocardial contractility. While heart rate decreased from 111 ± 3 to 73 ± 1 min⁻¹, cardiac output increased from 2.4 ± 0.1 to 3.1 ± 0.3 l/min, and stroke volume increased from 21 ± 1 to 41 ± 3 ml. +dP/dt_max increased by 25 ± 8% (37 vs. 31°C; p < 0.05 for all values). Systemic and pulmonary vascular resistance did not change significantly during cooling. Mild hypothermia exerts significant positive inotropic effects in human and porcine myocardium without increasing intracellular Ca²⁺-transients or SR Ca²⁺-content. These effects translate into improved hemodynamics parameters of left ventricular function. Received: 26 June 2000, Returned for revision: 20 July 2000, Revision received: 11 October 2000, Accepted: 17 October 2000     

Myosin heavy chain synthesis during the progression of chronic tachycardia induced heart failure in rabbits

Chronic tachycardia causes LV dilatation and dysfunction, with no hypertrophy. However, the contributing mechanisms responsible for the left ventricular (LV) remodeling in the absence of myocardial growth in this model of heart failure remain unclear. Therefore, the goal of the present study was to serially examine changes in LV function, steady state myosin heavy chain (MHC) mRNA levels, in vivo synthesis rates, and abundance with the progression of chronic tachycardia induced heart failure. Adult rabbits (3.5–4.5 kg) were studied after one, two, or three weeks of pacing ventricular tachycardia (VT; 400 bpm) and in controls (n=6 for all groups). LV fractional shortening was reduced by 30 % at week one and by over 50 % at week three of chronic VT. End‐diastolic dimension (EDD) increased at week two compared to controls (1.66 ± 0.10 vs 1.35 ± 0.11 cm, p < 0.05) and increased further at week three of VT (1.70 ± 0.06 cm, p < 0.05). The progressive changes in LV geometry and function with chronic VT were not associated with concomitant time dependent changes in LV mass or MHC mRNA levels. In contrast, MHC fractional synthesis rates increased and reached statistical significance at week three of VT compared to controls (8.3 ± 0.8 vs 5.5 ± 0.5 %/day, p < 0.05). Despite the stable or increased MHC protein synthesis rates, there was no change in MHC protein abundance at any point during the progression of VT induced heart failure, implicating enhanced MHC protein degradation. Thus, this study demonstrated that a contributory mechanism for the LV remodeling and lack of myocardial growth, which occurs with VT induced heart failure, is enhanced contractile protein degradative processes. Received: 17 July 1997 , Returned for revision: 20 August 1997, Revision received: 8 September 1997, Accepted: 7 October 1997     

Frequency dependent force generation correlates with sarcoplasmic calcium ATPase activity in human myocardium

Objective: In congestive heart failure both a decreased function of the sarcoplasmic Ca²⁺-ATPase and a negative force-frequency relationship have been shown. This study aimed to investigate a possible relationship between frequency potentiation, sarcoplasmic Ca²⁺-ATPase activity, and SERCA2 protein expression in human myocardium. Methods: Frequency potentiation was studied in electrically stimulated, isometric, left ventricular papillary muscle strip preparations (37°C, 0.5–3.0 Hz) from terminally failing (NYHA IV; n=5, dilated cardiomyopathy) and nonfailing (donor hearts, n=5) human myocardium. In the identical samples the Ca²⁺-ATPase activity (NADH coupled assay) and the protein expression of sarcoplasmic Ca²⁺-ATPase (SERCA2), phospholamban, and calsequestrin (western blot) were determined. The frequency dependent change in the force of contraction and V_max of the Ca²⁺-ATPase activity and the protein expression of SERCA2 were correlated with each other. Results: In terminally failing myocardium the force-frequency relationship was negative (2.0 Hz vs. 0.5 Hz: –0.2±0.1 ΔmN) contrasting a positive rate dependent potentiation of force in nonfailing tissue (2.0 Hz vs. 0.5 Hz: +0.8±0.2 ΔmN; p<0.01). In failing myocardium the corresponding maximal sarcoplasmic Ca²⁺-ATPase activity (V_max) was reduced significantly compared to nonfailing myocardium (174±24 vs. 296±31 nmol ATP/mg·min, p<0.01). The protein expression of SERCA2, phospholamban, and calsequestrin remained unchanged in failing myocardium. The maximal Ca²⁺-ATPase activity significantly correlated with the frequency dependent change in force of contraction (2 Hz vs. 0.5 Hz: r=0.88, p=0.001; 3 Hz vs. 0.5 Hz: r=0.84, p=0.004). No correlation between protein expression of SERCA2 and Ca²⁺-ATPase activity or change in force of contraction was observed. Conclusion: Due to a significant correlation between sarcoplasmic Ca²⁺-ATPase activity and frequency potentiation, the negative rate dependent force potentiation in human heart failure could be at least in part be attributed to decreased function of the sarcoplasmic Ca²⁺-ATPase. Received: 8 January 1998, Accepted: 2 June 1998     

Solute exchange in the rabbit myocardium: Ischaemia, reflow, and myocardial necrosis

Objective: Coronary occlusion in the rabbit reduces the delivery of particulate tracers to close to zero, but exchange of diffusible solutes, derived from non-arterial sources, continues at a significant level. We investigated the relationships between the exchange of diffusible solutes during coronary occlusion and the extent of myocardial necrosis and between duration of ischaemia and the extent of recovery of solute exchange during reflow. Methods: In an anaesthetised rabbit model of regional ischaemia and reflow, solute exchange is measured using the voltammetric hydrogen clearance technique. The area at risk and infarct size are determined ex vivo with monastral blue and nitroblue tetrazolium staining, respectively. Three groups are studied: control perfusion for 130 minutes (group A); 30 minutes coronary ligation followed by 90 minutes reflow (group B) and 40 minutes coronary ligation followed by 90 minutes reflow (group C). Results: There was no significant difference in area at risk between the groups B and C (50±2% and 45±5%; p=ns) or in infarct size when expressed relative to the area at risk (42±7% and 55±5%; p=ns). During coronary ligation hydrogen clearance remained constant at 22±4% of the control region in group B and 32±4% in group C, at the same time period in group A it was 87±2% (ANOVA=p<0.05, with a significant non-linear trend). Although the duration of ischaemia and the level of solute exchange during ischaemia did not correlate individually with the extent of myocardial necrosis, together they showed a significant correlation (ANOVA; p<0.05). Following coronary occlusion, hydrogen clearance recovered to 72±9% after 30 minutes ischaemia but only to 57±5% following 40 minutes ischaemia and was 95±2% in the control group (ANOVA between the three groups p<0.05 with a significant linear trend). Myocardial hydration fell in the apical region following coronary ligation by 27±5% in group B and by 25±5% in group C, and rose on reperfusion but only to 80±3% in group B and 83±3% in group C of their preligation values. Conclusion: In collateral deficient myocardium, the extent of myocardial necrosis is dependent on the level of solute exchange occurring during ischaemia. The level of solute exchange during reflow is dependent on the duration of ischaemia. Received: 4 December 1997, Returned for 1. revision: 12 January 1998, 1. Revision received: 16 April 1998, Accepted: 13 May 1998     

Differential value of adenosine myocardial contrast echocardiography and dobutamine stress echocardiography in evaluating functional significance of coronary artery stenosis in a porcine model

Aim Myocardial contrast echocardiography (MCE) during adenosine induced hyperemia is an experimental method that detects flow limiting coronary artery stenosis by visualizing myocardial perfusion defects. Noninvasive detection of flow limiting coronary artery stenosis in clinical routine is a frequent domaine of dobutamine stress echocardiography (DSE) visualizing ischemia related regional wall motion abnormalities. This study investigated the values of adenosine MCE and DSE in the detection of functionally significant coronary artery stenosis in an experimental open chest pig model. Methods A total of 28 proximal LAD stenoses were instrumented in 12 animals. Reduction of coronary blood flow reserve (Δ CFR [%]) was calculated as a marker of functional significance of coronary artery stenosis (mild to moderate stenosis: Δ CRF ≤ 50%; severe stenosis: Δ CFR > 50%). Fractional area shortening (FAS) and wall thickening (WT) were calculated to evaluate regional wall motion. Peak myocardial contrast intensities (PCI) were measured following aortic root injections of Levovist' to detect myocardial perfusion defects. Results As a group, severe stenosis significantly reduced wall motion response to dobutamine (Δ FAS: 12.0 ± 3.0%, vs. 20 ± 3.0% without stenosis, p < 0.05; Δ WT: 2.2 ± 0.9 mm vs. 0.0 ± 0.8 mm without stenosis, p < 0.05) and diminished myocardial opacification during hyperemia (PCI: 59 ± 8 units vs. 143 ± 16 units without stenosis, p < 0.05). Mild to moderate stenosis did not influence wall motion but reduced myocardial opacification (PCI 89 ± 14 units vs. 143 ± 16 units). PCI correlated more closely with alterations in CFR (r = −0.7, p < 0.0001) than did FAS (r = −0.5, p < 0.002) or WT (r = −0.2, p = 0.3). Conclusion Adenosine myocardial contrast echocardiography detects flow limiting coronary artery stenosis and compares favorably to regional wall motion analysis during dobutamine infusion. Received: 22 May 2000 / Returned for 1. revision: 26 June 2000 / 1. Revision returned: 11 September 2000 / Returned for 2. revision: 11 October 2000 / 2. Revision returned: 21 December 2000 / Accepted: 15 January 2001     

23Na NMR demonstrates prolonged increase of intracellular sodium following transient regional ischemia in the in situ pig heart

This study tests the hypothesis that Na⁺ _i increases during regional ischemia in the in situ pig heart. An extracorporeal shunt was created between the carotid artery and the left anterior descending artery of 14 open chest pigs. ²³Na and ³¹P NMR spectroscopy measured myocardial Na⁺ _i and high energy phosphates (HEPs). The protocol consisted of three 40 min periods: pre-ischemia (shunt pressure, 76±23 mmHg (S.D.)), ischemia (shunt pressure, 25±7 mmHg), and post-ischemia (shunt pressure, 53±11 mmHg). The pre-ischemia Na⁺ _i concentration was 6.7±4.2 mM. Phosphocreatine (PCr) was 15.3±0.5 mM, ATP 9.4±0.4 mM, inorganic phosphate (Pi) 1.5±0.2 mM, and pH_i 7.16±0.09. At the end of ischemia Na⁺ _i had increased to 10.5±2.8 mM (p<0.0002); PCr decreased to 5.9±2.1 mM (p<0.0002); ATP was 6.5±0.5 mM (p<0.003); Pi had increased to 6.3±1.0 mM (p<0.0002), and pH_i was 6.41±0.06 (p<0.0002). During the first 10 min of the reperfusion, Na⁺ _i increased further to 12.4±2.8 mM (p<0.025), whereas HEPs all returned to pre-ischemic values. Na⁺ _i increases during regional ischemia in the in situ pig heart, suggesting reduced Na⁺/K⁺ ATPase activity. While ATP probably does not limit Na⁺/K⁺ ATPase activity, increases in Pi and decreases in pH_i may reduce Na⁺/K⁺ ATPase activity. Additional Na⁺ _i increases during reperfusion suggest either augmented Na⁺ influx or decreased Na⁺ efflux. Received: 25 May 1998, Returned for revision: 22 June 1998, Revision received: 20 August 1998, Accepted: 15 September 1998     

Magnetocardiographic QT dispersion during cardiovascular autonomic function tests

QT dispersion is considered to reflect nonhomogeneity of ventricular repolarization. The autonomic nervous system modulates QT interval duration, but the effect may not be spatially homogenous. Magnetocardiography (MCG) registers the weak magnetik fields generated by myocardial electric currents with high localizing accuracy. We studied the effect of rapid cardiovascular autonomic nervous adjustment on QT dispersion in MCG. Ten healthy male volunteers were monitored during deep breathing, the Valsalva maneuver, sustained handgrip, hyperventilation, the cold pressor test and mental stress. 67 MCG channels and 12 ECG leads were recorded simultaneously. A computer algorithm was used for QT interval measurements. QT dispersion was defined as maximum – minimum or standard deviation of the QT_peak and QT_end intervals. In MCG the QT_end dispersion increased during deep inspiration compared with deep expiration (96±19 ms v 73±27 ms, p=0.05). Magnetic QT dispersion tended to increase during the bradycardia phase of the Valsalva maneuver, but the change was obvious only for QT_end (55±26 ms v 76±29 ms, p<0.05) Other tests had no significant effect on QT dispersion, not even the cold pressor test, although it causes strong sympathetic activation. Magnetic and electric QT_peak and QT_end intervals correlated closely (r=0.93 and 0.91), whereas the QT dispersion measures showed no correlation. In conclusion, magnetic QT dispersion is not modified by rapid changes in autonomic tone, but maneuvers involving deep respiratory efforts and changes in ventricular loading affect QT dispersion measurements. Received: 4 April 2000 Returned for revision: 2 May 2000 Revision received: 20 June 2000 Accepted: 10 July 2000     

Coronary artery distensibility and compensatory vessel enlargement--a novel parameter influencing vascular remodeling?

Vascular remodeling implies the concept of compensatory vessel enlargement to preserve luminal dimensions during atheromatous plaque development. However, negative remodeling, i.e. vessel shrinkage in response to plaque accumulation has also been described. So far, the factors influencing positive or negative remodeling are uncertain. We hypothesized that vascular distensibility, a measure of vessel compliance, is related to compensatory enlargement. In 58 patients undergoing intravascular ultrasound interrogation of a de novo lesion prior to coronary intervention, the cross-sectional vessel area (VA), lumen area (LA) and plaque area (PA = VA minus LA) were measured at end diastole and end systole at the lesion site and at the proximal and distal reference segments. Positive remodeling was defined to be present when the VA at the lesion was > 1.05 times larger than that at the proximal reference (group A), negative remodeling when the VA at the lesion was < 0.95 of the reference site (group C) and in-between was considered to be intermediate (group B). Vessel compliance was measured by calculating vascular distensibility. Results showed a similar LA at the lesion site in all groups (4.18 ± 2.18 vs. 4.36 ± 1.19 vs. 3.74 ± 1.81 mm², NS) while VA and PA were significantly larger in group A (17.19 ± 5.08 vs. 14.22 ± 3.66 and 12.45 ± 4.82 mm², p = 0.005 and 13 ± 4.55 vs. 9.95 ± 3.58 and 8.7 ± 3.83, p = 0.003, respectively). Vascular distensibility at the proximal reference segment was significantly greater in group A (3.55 ± 2.67 vs. 1.25 ± 1.03 and 0.85 ± 0.73 mmHg⁻¹, p < 0.001) with a positive correlation between remodeling and distensibility (R = 0.52, p < 0.001). In a multiple regression model including clinical and lesional factors, distensibility was the only predictor of remodeling. In conclusion, these results suggest that compensatory vessel enlargement occurs to a greater degree in patients with increased coronary artery distensibility, which appears to be a predictor for positive remodeling. Received: 14 September 2000, Returned for revision: 30 October 2000, Revision received: 8 January 2001, Accepted: 24 January 2001     

Routine arterial oxygen saturation monitoring is not necessary during transesophageal echocardiography

Background: Transesophageal echocardiography (TEE) is now an established adjunct to routine echocardiography, its diagnostic impact making it an invaluable first-line diagnostic procedure in many cardiac conditions. However, there is no unanimity in the way the transesophageal procedure is carried out, especially with regard to the need for antibiotic prophylaxis, sedation, and the monitoring of oxygen saturation. Hypothesis: This study was prospectively undertaken (1) to determine the presence and magnitude of oxygen desaturation and (2) the changes in heart rate and blood pressure following sedation for routine TEE in an unselected and consecutive group of patients to identify those at high risk. Methods: Arterial oxygen saturation, heart rate, and systolic, diastolic, and mean blood pressure were monitored in 106 consecutive patients undergoing routine transesophageal echocardiography. Ninety-four (89%) patients received intravenous sedation with midazolam. Results: Three min after midazolam administration there was a drop in oxygen saturation from 97 ± 2.5 to 95 ± 2.9 (p<0.001), in systolic blood pressure from 139 ± 19.5 to 124.8 ± 22.2 mmHg (p<0.001), in diastolic blood pressure from 86.6 ± 19.9 to 77.5 ± 17.7 mmHg (p<0.001), and in mean blood pressure from 108.3 ± 18 to 95.6 ± 28.8 mmHg (p<0.001). After introduction of the transesophageal probe and during the examination, there was a further drop in oxygen saturation with a maximum drop at the 15th min of the examination (93.7 ± 3.7 vs. 97 ± 2.5, p<0.001). The maximum blood pressure drop occurred at the 12th min into recovery: systolic blood pressure dropped from 139 ± 19.5 to 118 ± 20.8 mmHg (p<0.001), diastolic blood pressure from 86.6 ± 16.9 to 75.8 ± 17.9 mmHg (p<0.005), and mean blood pressure from 108.3 ± 18 to 92.5 ± 19.4 mmHg (p<0.01). Patients with congestive heart failure had a greater drop in oxygen saturation compared with patients who were not in heart failure (p<0.01). Twelve patients did not receive any sedation; however, they all showed a drop in oxygen saturation from 97.8 ± 2.3 to 94.6 ± 3.4 (p<0.001), with a maximum drop at the 15th min during the transesophageal examination. Conclusion: In patients with no chronic obstructive airway disease who are not in congestive heart failure, routine oxygen saturation monitoring is not deemed necessary during transesophageal examination. The cause of hypoxemia during the procedure is not only related to sedation but also to esophageal intubation.     

Preconditioning-induced cardioprotection and release of the second messenger inositol (1,4,5)-trisphosphate are both abolished by neomycin in rabbit heart

The mechanisms responsible for infarct size reduction with preconditioning remain controversial. Our aim was to determine whether release of the second messenger inositol (1,4,5)-trisphosphate (Ins(1,4,5)P₃) during the preconditioning stimulus may play a role. To test this concept, Langendorff-perfused rabbit hearts underwent sham perfusion, 5 min of coronary artery occlusion (CO), or 5 min of CO+infusion of neomycin, an agent which inhibits formation of Ins(1,4,5)P₃. Direct quantitation (by competitive binding assay) revealed a 2-fold increase in Ins(1,4,5)P₃ content with brief ischemia vs shams (0.69±0.14 vs 0.34±0.05 pmol/mg tissue; p<.05) that was blocked by neomycin (0.15±0.04 pmol/mg). Infarct size (by tetrazolium staining) was assessed in additional hearts that underwent 30 min of sustained CO and 2 h of reperfusion. As expected, two 5-min episodes of preconditioning ischemia reduced infarct size versus controls (30±6% versus 63±3% of the myocardium at risk; p<.01). In contrast, infarct size was comparable (54–56% of the risk region) in neomycin-treated control and preconditioned hearts. These results demonstrate that myocardial Ins(1,4,5)P₃ content is increased in response to brief preconditioning ischemia and are consistent with the concept that Ins(1,4,5)P₃ may be a potential mediator of infarct size reduction with preconditioning in isolated rabbit heart. Received: 12 February 1998, Returned for revision: 1 April 1998, Revision received: 1 June 1998, Accepted: 12 August 1998     

Energy generation in hypertrophied postischemic myocardium Feasibility of prolonged inotropic stimulation with dopamine in hypertrophied reperfused left ventricles

Background Non-hypertrophied reversibly injured postischemic myocardium can be stimulated for a prolonged period without detrimental effects. Since no data on hypertrophied myocardium are available, our aim was to examine the effects of a prolonged postischemic positive inotropic stimulation on moderately hypertrophied left ventricles. Methods Using a Langendorrf-type isovolumically contracting isolated heart model, moderately hypertrophied (+50% of ventricular mass) hearts from spontaneously hypertensive rats (SHR) were investigated and compared to data from non-hypertrophied hearts of normotensive rats. A 30 minutes noflow ischemia was performed, and in the postischemic period dopamine was continuously administered for 20 minutes in order to stimulate the postischemic hearts to the control level of function. Data were compared to postischemic hearts without stimulation and to non-ischemic controls. After 50 minutes of reperfusion and cessation of the catecholamine steady state function, maximum contractile response, and high energy phosphates were determined. Results 30 minutes ischemia followed by 50 minutes reperfusion caused a significant reduction in developed LVP to 77.8±4.2% in SHR. Dp/dtmax was reduced to 67.0±2.3%. After cessation of dopamine stimulation developed LVP was 64.3±3.5% and dp/dtmax 69.3±3.7% in SHR. The double product was identically reduced in all postischemic groups. The contractile reserve was comparable in stimulated and non-stimulated postischemic SHR hearts. In hypertrophied myocardium, ATP was reduced to 1.1±0.1 μmol/gww (non-ischemic controls 2.5±0.3 μmol/gww) in unstimulated and to 1.0±0.1 μmol/gww in stimulated postischemic hearts. Comparably the ischemia-induced reduction in ATP in non-hypertrophied myocardium was 1.3 μmol/gww. Similar results were obtained for ADP and AMP. Creatine phosphate levels were normal in stimulated and non-stimulated postischemic myocardium of hypertrophied and non-hypertrophied hearts. Conclusion These results indicate that prolonged stimulation of stunned hypertrophied myocardium is feasible without detrimental effects on poststimulation contractile function. The energy generating apparatus is capable to deliver sufficient energy during stimulation of stunned hypertrophied hearts. Received: 28 July 1997, Returned for Revision: 4 September 1997, 1. Revision received: 20 October 1997, Accepted: 21 November 1997     

Preconditioning one myocardial region does not neccessarily precondition the whole rabbit heart

A previous study in dogs indicated that preconditioning (PC) of a specific myocardial region not only evoked a local cardioprotective effect but also rendered remote myocardium resistant to infarction. In the present study we devised a method to test for remote PC in the rabbit which it is not possible to ligate two separate coronary branches on the same heart. In situ hearts were subjected to PC with two cycles of 5-min regional ischemia/5-min reperfusion. Following this in vivo PC protocol, the hearts were removed and perfused on a Langendorff apparatus with crystalloid buffer. They then underwent 30 min of global ischemia with the entire left ventricle at risk followed by 2 h of reperfusion. At the end of the experiment the myocardium previously subjected to the in vivo PC protocol (preconditioned region) was identified as the tissue without fluorescence after fluorescent particles had been injected into the aortic root following reocclusion of the snared branch of the left coronary artery. Infarcted myocardium was identified by triphenyltetrazolium chloride staining. Tissue salvage was observed only in the preconditioned region where 13.2 ± 3.6 % of the myocardium infarcted as opposed to 44.6 ± 1.3 % in the remaining non-preconditioned left ventricular tissue (p < 0.05, n = 6). In sham-operated hearts (snare but no PC), infarction was similar in both the snared vessel's perfusion territory and the rest of the left ventricular myocardium (49.2 ± 6.5 % vs. 43.7 ± 3.7 %, n = 5). Hence PC of one myocardial region does not necessarily confer PC protection to all regions of the heart. Because remote PC could not be demonstrated in rabbits, this phenomenon may be species or protocol-specific, and should not be assumed to occur in man. Received: 11 April 2001, Returned for revision: 22 April 2001, Revision received: 15 May 2001, Accepted: 17 May 2001