Simultaneous in utero assessment of AV nodal and ventricular electrophysiologic parameters in the fetal sheep heart

Background Fetal tachyarrhythmias are usually of supraventricular origin. To investigate whether specific electrophysiologic properties of the fetal heart contribute to this preponderance by either favoring supraventricular tachycardias or by rendering ventricular tachycardias unlikely, we measured fetal electrophysiologic parameters in utero using transuterine fetal transesophageal electrocardiograms in fetal sheep. Since overdrive pacing may help to establish the mechanism of an arrhythmia and may be used to treat fetal tachycardias, different modes of transesophageal pacing in utero were also assessed. Methods and results Decapolar electrophysiology catheters were fetoscopically inserted into the esophagus of 9 fetal sheep (pregnancy duration 94 – 105 days, term = 145 days). Electrocardiograms were recorded simultaneously from all adjacent bipoles and from two pacing wires sutured onto the fetal shoulders. Pacing was attempted either via two adjacent electrodes of the intraesophageal catheter or via the most distal and most proximal electrode. Fetal cycle length, PQ, and QT intervals were close to (approx. 75 %), but fetal QRS duration was < 20 % of maternal values, thus shifting the relation between activation and repolarization towards longer excitation wave lengths. Fetal QT dispersion was small (≤ 10 ms). Atrial pacing was achieved in all fetuses using distant electrodes, and with lower thresholds when compared to closely spaced bipolar electrodes (p < 0.05). Conclusions (I) An altered relation between ventricular activation and repolarization and a low dispersion of ventricular repolarization may protect the fetal heart against ventricular reentrant tachycardias. (II) Relatively normal fetal AV nodal conduction delay already provides one of the prerequisites for supraventricular reentrant tachycardias involving the AV node at this stage of fetal development. (III) High-rate esophageal pacing of the fetal atria is best achieved using widely spaced bipolar pacing electrodes. Received: 26 July 2000, Returned for 1. revision: 16 August 2000, 1. Revision received: 28 November 2000, Returned for 2. revision: 18 December 2000, 2. Revision received: 23 January 2001, Accepted: 24 January 2001     

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     

Inducible lethal ventricular arrhythmias in swine with pacing-induced heart failure

Introduction: Rapid pacing-induced heart failure provides an excellent animal model for the study of heart failure. We studied the development of ventricular tachyarrhythmias using programmed stimulation in a pacing-induced heart failure model. We also studied action potential characteristics and the relationship between action potential and heart rate. Methods and results: Ten pigs were instrumented and were studied before the onset and every week after rapid pacing was instituted. Weekly echocardiograms and programmed stimulation were done in a sedated state. In vitro electrophysiologic studies were done on left ventricular myocardium in 4 heart-failure animals and 4 controls. All animals developed progressive heart failure with left ventricular dilatation and reduced percentage fractional shortening. No arrhythmias were induced at baseline or the first and second weeks. Ventricular fibrillation was induced in one animal on the third week and 4 animals on week 4, while there was no appreciable worsening in echocardiographic indices of ventricular dysfunction between weeks 3 and 4. Ventricular effective refractory period was unchanged during the 4 weeks. In vitro studies showed action potential prolongation in heart failure myocardium. However, action potential duration at pacing rates > 100 bpm were similar to controls. No early or delayed afterdepolarizations were observed. Conclusion: This study demonstrated an increased susceptibility to ventricular fibrillation with the development of heart failure which was not related to the degree of ventricular disfunction. Also, the normalization of action potential duration at higher heart rates suggests that the increased incidence of inducible ventricular fibrillation in this model may not be solely due to prolonged action potential duration. Received: 4 January 1999, Returned for 1. revision: 29 January 1999, 1.Revision received: 26 May 1999, Accepted: 15 June 1999     

Effects of BIIB513 on ischemia-induced arrhythmias and myocardial infarction in anesthetized rats

Na⁺/H⁺ exchange (NHE) plays an important role in the regulation of the intracellular pH (pH_i) and in cardiac cell injury induced by ischemia and reperfusion. In the present study, we investigated the effects of BIIB513, a selective NHE-1 inhibitor on myocardial ischemia induced arrhythmias and myocardial infarction, provoked by 30 minutes of left main coronary artery occlusion followed by 2 hours of reperfusion in an anesthetized rat model. Intravenous administration of BIIB513 (0.01–3.0 mg/kg) did not induce changes in blood pressure or heart rate. BIIB513 (0.01, 0.1, 0.3, 1.0, 3.0 mg/kg) given prior to the coronary artery occlusion dose-dependently reduced ventricular premature beats, ventricular tachycardia, and a complete suppression of ventricular fibrillation down to the dose of 0.1 mg/kg. BIIB513 (0.01, 0.1, 0.3, 1.0, 3.0 mg/kg) given prior to the coronary artery occlusion dose-dependently reduced the infarct size with an ED50 value of 0.16 mg/kg. BIIB513 (1.0 mg/kg) given prior to reperfusion also reduced infarct size by 47.3 ± 13.1%. The reduction in infarct size was accompanied by a decrease in circulating levels of creatine phosphokinase (CPK). In conclusion, the present study demonstrates the cardioprotective ability of NHE-1 inhibition during myocardial ischemia and reperfusion by reducing serious ventricular arrhythmias and myocardial infarct size in anesthetized rats. Received: 18 November 1999, Returned for 1.revision: 9 December 1999, 1.Revision received: 2 May 2000, Returned for 2.revision: 24 May 2000, 2.Revision received: 5 June 2000, Accepted: 7 June 2000     

A role of PKC in the improvement of energy metabolism in preconditioned heart

Objectives. A possible link between activation of PKC and improvement of energy metabolism during reperfusion in ischemic preconditioning hearts was examined. Methods. Isolated perfused rat hearts were preconditioned by 5-min ischemia and 5-min reperfusion in the presence and absence of a PKC inhibitor polymyxin B (50 μM) and then subjected to 40-min sustained ischemia and subsequent 30-min reperfusion. In another set of experiments, the hearts pretreated with and without a PKC activator PMA (15 pmol/5 min) were subjected to the sustained ischemia and reperfusion. Myocardial high-energy phosphates, glycolytic intermediates and mitochondrial oxygen consumption capacity were determined at appropriate experimental sequences. Results. Preconditioning enhanced the recovery of cardiac function such as left ventricular developed pressure, heart rate and rate-pressure product of the reperfused heart, suppressed the release of creatine kinase, enhanced the reperfusion-induced restoration of myocardial high-energy phosphates, attenuated the reperfusion-induced accumulation in glucose 6-phosphate and fructose 6-phosphate contents, abolished the ischemia-induced increase in tissue lactate content and prevented the ischemia-induced decrease in mitochondrial oxygen consumption capacity. Treatment of the perfused heart with PMA mimicked the effects of preconditioning on post-ischemic contractile function, enzyme release, levels of myocardial energy store, glycolytic intermediates and lactate, and mitochondrial function. Polymyxin B-treatment abolished the preconditioning-induced recovery of post-ischemic contractile function, the suppression of the release of CK, the restoration of myocardial energy store, and the preservation of mitochondrial function, whereas it did not cancel the improvement of glycolytic intermediate levels and the reduction in tissue lactate accumulation. Post-ischemic contractile function was closely related to restoration of high-energy phosphates and mitochondrial oxygen consumption capacity in all hearts subjected to ischemia/reperfusion. Conclusion. The results suggest that activation of PKC and preservation of mitochondrial function are closely linked with each other in the preconditioned heart, which may lead to the improvement of post-ischemic contractile function. Received: 29 January 1999, Returned for 1. revision: 26 February 1999, 1. Revision received: 27 April 1999, Returned for 2. revision: 18 May 1999, 2. Revision received: 12 July 1999, Returned for 3. revision: 26 July 1999, 3. Revision received: 25 October 1999, Accepted: 3 November 1999     

Rp-cAMPS has ho effect on adenosine A1 receptors in guinea-pig cardiomyocytes

Rp-cAMPS, a protein kinase A inhibitor, is used in the investigation of the cAMP-dependent systems. A report by Musgrave et al. (11) has suggested that Rp-cAMPS may also act on adenosine receptors. To determine whether this occurs in guinea-pig ventricular myocytes, Rp-cAMPS was applied in the presence and absence of DCPCX, an adenosine A₁ receptor antagonist. The isoprenaline-induced response was significantly decreased by Rp-cAMPS and the effect was not altered by the presence of DCPCX. Therefore Rp-cAMPS has no effect on cell contraction via adenosine A₁ receptors and can reliably be used to investigate cyclic AMP-dependent systems in isolated cardiac myocytes. Received: 23 April 1999, Returned for 1. revision: 26 May 1999, 1. Revision received: 23 August 1999, Returned for 2. revision: 28 September 1999, 2. Revision received: 15 November 1999, Accepted: 17 November 1999     

Effects of preconditioning on myocardial interstitial levels of ATP and its catabolites during regional ischemia and reperfusion in the rat

The interstitial accumulation of adenine nucleotide breakdown products (ANBP) in the myocardium during ischemia has been shown to provide a useful index of the ischemic injury, whereas reperfusion ANBP washout rate has been regarded as an index of reperfusion damage. The purpose of this study was, using cardiac microdialysis, to examine in the rat model of regional ischemia/reperfusion the relationship between the duration of ischemia and these indices and to assess the profile of interstitial ATP concentrations and the beneficial effects of ischemic preconditioning (IP). The rats underwent 10, 20, 30 or 40 min of coronary artery occlusion and 50 min of reperfusion. Regional ischemia, with its duration, provoked a progressive increase in dialysate ANBP in the ischemic zone. The rate of purine washout during reperfusion exponentially declined with an increase in duration of the ischemic period. IP, induced by three 5-min episodes of ischemia, each separated by 5 min of reperfusion, significantly reduced the accumulation of ANBP during the 30-min period of sustained ischemia and resulted in a marked acceleration of reperfusion ANBP washout, indicating the improvement of postischemic microcirculation. These effects were suggested to be, at least in part, responsible for the infarct size limitation observed. Using the relationship between the duration of ischemia and ANBP washout rate, it could be demonstrated that IP produced similar facilitation of purine washout as shortening of the ischemic period in nonpreconditioned rats from 30 to approximately 7 min. Regional 20-min ischemia induced an early peak increase in interstitial fluid ATP which correlated with the maximal incidence of ventricular arrhythmias, whereas IP abolished both ATP release and arrhythmias during the sustained ischemia. These findings suggest that ATP may be an important mediator of ischemia-induced ventricular arrhythmias. Received: 20 April 1999, Returned for 1. revision: 11 May 1999, 1. Revision received: 23 June 1999, Returned for 2. revision:15 July 1999, 2. Revision received: 27 September 1999, Accepted: 29 September 1999     

Cyclic GMP attenuates cyclic AMP-stimulate inotropy and oxygen consumption in control and hypertrophic hearts

We tested the hypothesis that increasing myocardial cyclic GMP would attenuate cyclic AMP induced positive inotropy and O₂ consumption, in part, through changes in cyclic AMP and that renal hypertension-induced cardiac hypertrophy (HYP) would alter this relationship. Anesthetized, open chest rabbits (N = 48) were divided into four groups of control (CON) and HYP animals which received vehicle (VEH), isoproterenol 10⁻⁶M (ISO), 3-morpholinosyndnonimine 10⁻⁴M, (SIN-1), or a combination of ISO+SIN-1. Coronary blood flow (micro-spheres) and O₂ extraction (microspectrophotometry) were used to determine O₂ consumption in both subepicardium (EPI) and subendocardium (ENDO). Left ventricular change in wall thickness (%) was increased significantly by ISO in both CON (16 ± 4 to 31 ± 6) and HYP (17 ± 2 to 24 ±3). Percent change in wall thickness was similar in the CON, SIN-1, and ISO+SIN-1 groups. Myocardial O₂ consumption (ml O₂/min/100 g) was increased by ISO in CON (10.3 ± 1.0 to 13.6 ± 2.0 EPI; 10.9 ± 1.0 17.1 ±1.7 ENDO) and HYP (8.2 ± 1.4 to 12.3 ± 2.2 EPI; 6.6 ± 1.4 to 14.8 ± 1.8 ENDO). Oxygen consumption was unaffected by SIN-1 in CON and HYP animals. ISO+SIN-1 caused attenuated ISO-induced increases in O₂ consumption in CON in EPI and ENDO, and in EPI in HYP. Cyclic GMP (pmol/g) was unchanged by ISO in CON and HYP, and increased by SIN-1 in CON (8.1 ± 1.3 to 19.2 ± 2.3 EPI) and HYP (9.1 ± 1.5 to 12.8 ± 2.0 EPI). Cyclic GMP remained elevated with ISO+SIN-1 in both groups. Cyclic AMP (pmol/g) was increased significantly by ISO in CON (496 ± 43 to 725 ± 106 EPI; 534 ± 44 to 756 ± 148 ENDO) and insignificantly in HYP (435 ± 50 to 566 ± 35 EPI; 497 ± 51 to 583 ± 47 ENDO). Cyclic AMP levels were unaffected by SIN-1 in either group. Isoproterenol induced increases in cyclic AMP were blunted by ISO+SIN-1 in CON (496 ± 43 to 537 ± 59 EPI) and not affected in HYP. The current study demonstrated attenuation of cyclic AMP mediated increased inotropy and O₂ consumption by increasing cyclic GMP, which appeared, in part, related to cyclic GMP-induced reduction in cyclic AMP. This effect of cyclic GMP on cyclic AMP was not observed in myocardial hypertrophy. Received: 4 January 1999, Returned for 1. revision: 29 January 1999, 1. Revision received: 30 March 1999, Returned for 2. Revision: 3 May 1999, 2. Revision received: 3 May 1999, Returned for 3. Revision: 12 May 1999, 3. Revision received: 23 June 1999, Returned for final revision: 7 July 1999, Accepted: 22 July 1999     

Endocardial versus epicardial differences of sarcoplasmic reticulum Ca2+-ATPase gene expression in the canine failing myocardium

It is unknown whether the transmural heterogeneity of sarcoplasmic reticulum (SR) Ca²⁺-ATPase gene expression is present within the left ventricular (LV) wall. Moreover, the changes of transmural distribution have not been examined in the failing hearts. We thus quantified steady-state mRNA abundance of SR Ca²⁺ regulatory proteins by Northern blot analysis in both subendocardial and subepicardial LV layers from normal and rapid pacing-induced heart failure (HF) dog hearts. For normal LV, Ca²⁺-ATPase mRNA abundance (normalized to glyceraldehyde-3-phosphate dehydrogenase [GAPDH] mRNA) was significantly reduced in the subendocardium, whereas calsequestrin mRNA abundance was comparable between the two layers. For HF LV, Ca²⁺-ATPase mRNA abundance in the subendocardium was also reduced compared to the subepicardium. However, the endocardium to epicardium ratio was comparable between control and HF (0.62 ± 0.08 vs. 0.65 ± 0.07; p = NS). Therefore, the transmural gradient of this gene was constant in both control and HF. Even though the data on the transmural heterogeneity of protein level is not available, the subendocardium contained significantly less Ca²⁺-ATPase mRNA, which might contribute, at least in part, to the transmural gradients of biochemical and mechanical function. Received: 8 February 1999, Returned for revision: 8 March 1999, Revision received: 1 April 1999, Accepted: 23 April 1999     

Endogenous adenosine suppresses norepinephrine-induced ventricular arrhythmias in rat heart

Adenosine is an antiarrhythmic substance particularly effective in catecholamine-dependent tachycardias. Although endogenous adenosine substantially accumulates in catecholamine-stimulated hearts, little is known about the antiarrhythmic potency of endogenous adenosine in this condition. Therefore, we sought to demonstrate a potential antifibrillatory effect of endogenous adenosine either by blockade of adenosine receptors with 8-phenyltheophylline (8-PT) or by suppression of endogenous adenosine release with nitrobenzyl-6-thioinosine (NBTI). The study was performed in spontaneously beating Langendorff-perfused rat hearts. Adenosine release into the effluent was determined by HPLC methods. Catecholamine stimulation was induced by perfusing the hearts with norepinephrine (1 μmol/l) for 30 min, which caused ventricular tachycardia (VT) in 31% and ventricular fibrillation (VF) in 25% of control hearts (n=35). When 8-PT (10 μmol/l) was added to the perfusion buffer prior to norepinephrine, the incidence of VT and VF increased to 79 and 68%, respectively. The addition of 8-PT did not affect the catecholamine-dependent formation of adenosine. Perfusion of the hearts with NBTI (10 μmol/l) prior to norepinephrine reduced adenosine release and increased the occurrence of both VT (65%) and VF (40%). In summary, the results indicate that adenosine is an endogenous antiarrhythmic substance, which accumulates in catecholamine-stimulated myocardium to a level, which effectively suppresses the occurrence of ventricular arrhythmias. Received: 26 November 1997, Returned for 1. revision: 18 December 1997, 1. Revision received: 15 January 1998, Returned for 2. revision: 29 January 1998, 2. Revision received: 18 February 1998, Accepted: 18 February 1998     

Early rather than delayed administration of lisinopril protects the heart after myocardial infarction in rats

Background:ACE inhibitors have shown beneficial results in several studies after myocardial infarction (MI). However, this studies have shown conflicting results about the ideal starting time of the ACE inhibitors administration after MI and the importance of infarct size. Objectives: This study was designed to assess the long-term effects of lisinopril on mortality, cardiac function, and ventricular fibrosis after MI, in rats. Methods: Lisinopril (20 mg/kg/day) was given on day 1 or 21 days after coronary occlusion in small or large infarctions. Results: The mortality rate was reduced by 39% in early treatment and 30% in delayed treatment in comparison to the untreated rats. Early treatment reduced cardiac dysfunction in small MIs; however, delayed treatment did not. No statistical difference was observed among the groups for large MIs. No statistical difference was observed among the groups with large or small MIs on myocardial hydroxyproline concentration. Conclusions: Both early and delayed treatments with lisinopril increased survival. Treatment exerts no marked effects on fibrosis; early treatment has exerted beneficial influences on cardiac function whereas delayed treatment had no consistent effects. The protective effect of lisinopril is detectable only in small (< 40% of LV) MIs. Received: 6 May 1999, Returned for 1. revision: 28 May 1999, 1. Revision received: 20 July 1999, Returned for 2. revision: 26 August 1999, 2. Revision received: 28 September 1999, Accepted: 29 September 1999     

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     

Hyperthyroidism is associated with preserved preconditioning capacity but intensified and accelerated ischaemic contracture in rat heart

Background: The present study was undertaken to define the effects of thyroxine administration on ischaemic preconditioning (PC) and the ischaemic contracture. Methods: Hyperthyroidism was induced by administration of L-thyroxine in rats (THYR) while normal animals served as controls (NORMa). Isolated rat hearts were perfused in a Langendorff preparation. NORMa control (n = 16) and THYR control (n = 9) hearts underwent 20 min of ischaemia and 45 min reperfusion while NORMa PC (n = 16) and THYR PC (n = 14) were subjected to PC before ischaemia. Additional normal hearts were subjected to 30 min of ischaemia with and without PC, NORMb control, n = 8 and NORMb PC, n = 6. Postischaemic recoveries of left ventricular (LV) developed pressure were expressed as % of the initial value (LVDP%). Severity of contracture was measured by the time (Tmax) and magnitude (Cmax) of peak contracture. Results: LVDP% was significantly higher after PC, both in NORMa and THYR rats. In NORMa control hearts, ischaemic contracture had not yet reached a plateau at 20 min of ischaemia. Contracture appeared earlier in THYR control and PC than in NORMa control and PC groups. Tmax was 22.1 (0.9) vs 16.8 (1.4) min for NORMb control and PC, p < 0.05 and 12.5 (1.0) vs 9.3 (1.1) min for THYR control and PC hearts, p < 0.05. Tmax was earlier in both THYR groups compared to NORMb groups, p < 0.05. Cmax was significantly higher in both THYR groups compared to both NORMb groups. Conclusion: Ischaemic contracture is both accelerated and accentuated in thyroxine treated hearts while preconditioning capacity is preserved. Preconditioning and thyroxine administration shorten Tmax in an additive way, whereas Cmax in hyperthyroid hearts did not further increase by preconditioning. Received: 7 January 1999, Returned for 1. revision: 1 February 1999, 1. Revision received: 4 March 1999, Returned for 2. revision: 31 March 1999, 2. Revision received: 19 April 1999, Accepted: 21 April 1999     

Role of nonsustained ventricular tachycardia and programmed ventricular stimulation for risk stratification in patients with idiopathic dilated cardiomyopathy

Background: The prognostic role of asymptomatic nonsustained ventricular tachycardia (NSVT) and programmed ventricular stimulation (PVS) in patients with idiopathic dilated cardiomyopathy (IDC) remains controversial. Methods: The prognostic significance of ventricular arrhythmias, ejection fraction, NYHA class, atrial fibrillation and age for overall and sudden death mortality was prospectively studied in 157 patients with IDC (group 1) free of documented sustained ventricular arrhythmia and syncope. In 99 patients with asymptomatic NSVT (group 2), PVS with 2 – 3 extrastimuli was performed. Non-inducible patients were discharged without specific antiarrhythmic therapy, whereas those with inducible monomorphic ventricular tachycardia were implanted with an ICD. Results: In group 1, 48% of patients had NSVT. Overall and sudden death mortality were significantly higher in patients with NSVT (34.2 vs. 9.8%, p = 0.0001 and 15.8 vs. 3.7%, p = 0.0037; follow-up 22 ± 14 months). Multivariate analysis revealed that NSVT independently predicts both overall and sudden death mortality (p = 0.0021 and .0221, respectively; adjusted for EF, NYHA class and age). In group 2, inducibility of sustained ventricular tachyarrhythmia was 7%, but sustained monomorphic VT occurred in 3% only. Two of 7 inducible patients experienced arrhythmic events during a follow-up of 25 ± 21 months (positive predictive value 29%). Overall and sudden death mortality were 29% and 0% in the inducible group vs. 17 and 4% in the non-inducible group. Both overall and sudden death mortality were signi.cantly lower in non-inducible patients from group 2 as compared to patients from group 1 with NSVT (p = 0.0043 and 0.0048), most likely due to a more common use of betablockers and a higher EF in the former group (p < 0.001, respectively). Conclusions: In patients with IDC, NSVT independently predicts both overall and sudden death mortality. Due to a low inducibility rate and a poor positive predictive value, PVS seems inappropriate for further arrhythmia risk assessment. However, in spite of documented NSVT, the incidence of SCD in patients on optimized medical treatment including betablockers seems to be very low, questioning the need for specific arrhythmia risk stratification. Received: 21 August 2002, Returned for revision: 24 September 2002, Revision received: 8 October 2002, Accepted: 7 November 2002, Published online: 12 May 2003 Correspondence to: R. Becker, MD     

Visualization and comparison of drug effects after local paclitaxel delivery with different catheter types

Background: The microtubule stabilizing compound paclitaxel has proved to have potent antiproliferative effects on smooth muscle cells both in vitro and in vivo. It induces cellular modifications that result in reduced proliferation, migration and signal transduction by shifting the cellular microtubule equilibrium towards assembly. We therefore reasoned that a visualization of the altered cytoskeleton could enable an evaluation of the drug effects following local drug delivery. Methods and results: 3 catheters – the porous balloon, the microporous balloon and the double balloon catheter – were chosen for this study representing the spectrum from passive to active, pressure-driven delivery. After the induction of a defined plaque in the right carotid arteries of 40 New Zealand rabbits by electrical stimulation, 32 animals underwent balloon dilatation and 8 animals served as pre-interventional control group with electrostimulation only. In 24 animals (n = 8 in each group) subsequent local paclitaxel delivery (10 μmol/L) was performed. 8 animals served as control with angioplasty only. Vessels were excised 1 week following intervention. Immunohistochemistry with antibodies against bromodeoxyuridine, alpha-actin, macrophages, von Willebrand factor and α-tubulin was performed. Cytoskeletal changes were analyzed by electron microscopy. Tubulin staining and electron microscopy revealed changes with distinct staining patterns for the different catheters. Specific catheter-induced injuries could be identified for the porous and double balloon catheter. Intimal proliferation, percentage of macrophages and extent of injury favor the double balloon catheter for local paclitaxel delivery. Conclusions: The alterations of the cytoskeleton induced by paclitaxel allowed for the detection of drug action by staining of tubulin and electron microscopy. This enables an evaluation of transfer, distribution and drug effects directly in the vasculature without marker substances. The double balloon catheter appears to be best suited for local paclitaxel therapy. Received: 3 November 1998, Returned for 1. revision: 11 December 1998, 1. Revision received: 10 February 1999, Returned for 2. Revision: 22 March 1999, 2. Revision received: 8 June 1999, Accepted: 1 July 1999     

Load-induced changes in repolarization: evidence from experimental and clinical data

The high incidence of arrhythmias in patients with heart failure, hypertension, valvular heart disease, or mitral walve prolapse suggests a strong link between wall motion abnormalities and arrhythmias. A potential common mechanism underlying these observations may be that overload leads to electrophysiologic changes and facilitates arrhythmias. This article summarizes the interaction between changes in atrial and ventricular loading conditions and repolarization. Most experimental and clinical studies demonstrated 1) a reduction of action potential duration and refractoriness, 2) development of early afterdepolarizations, and 3) ectopic beats originating from these afterdepolarizations. Discrepancies between studies are related to different study designs, i.e., varying magnitude, velocity, and timing of increased load, the level of repolarization at which action potential duration is measured as well as different animal species. Direct effects of increased load on repolarization are most likely caused by activation of stretch-activated nonselective cation ion channels and changes in calcium handling. Current antiarrhythmic drug therapy is aimed at electrical disorders as the primary cause of arrhythmias. If mechanical disorders play a central role in the genesis of cardiac arrhythmias, future treatment should be directed at restoring a more normal mechanical function of the heart. Additional studies will further clarify the nature and clinical significance of load-related changes in repolarization and arrhythmogenesis. Received: 20 November 2000 / Returned for revision: 20 December 2000 / Revision received: 2 January 2001 / Accepted: 8 January 2001     

Clofilium in the isolated perfused rabbit heart: A new model to study proarrhythmia induced by class III antiarrhythmic drugs

Objective: The clinical usefulness of class III antiarrhythmic drugs for the treatment of tachyarrhythmias is limited by their potential proarrhythmic effects, mainly torsades-depointes (TdP). The goal of this experimental study was to develop an isolated whole-heart model exhibiting typical characteristics of class III drug-induced ventricular arrhythmias. Methods: Isolated rabbit hearts were perfused with a Krebs-Henseleit buffer containing 10 μM clofilium and then exposed to a modified Krebs-Henseleit buffer with 2.0 mM K² and 0.5 mM Mg²⁺. Hearts subjected to either clofilium alone or modified buffer alone were used as controls. Results: Under clofilium the QT interval increased from 187±16 to 282±33 ms. Within 8 to 25 s after the change of the perfusate, ventricular arrhythmias developed in all hearts associated with a further QT prolongation to 380±73 ms when the first ventricular extrasystole occurred. Simultaneously, the monophasic action potential durations increased relatively more during late repolarization; from 99±21 to 110±25 ms (+11%) at 50% repolarization, from 143±24 to 178±40 ms (+24%) at 70%, and from 200±30 to 275±53 ms (+38%) at 90%. The predominant rhythm was polymorphic with either two alternating or multiple QRS morphologies exhibiting the characteristic features of torsades-depointes. All control hearts stayed in normal sinus rhythm. Conclusion: Under the conditions selected, the isolated perfused rabbit heart represents a useful experimental approach to study the proarrhythmic effects of class III agents. This model provides a convenient way to manipulate the ionic and pharmacologic millieu in a preparation conserving the functional anatomy of the whole organ without interference by cardiovascular reflexes. It might be useful for analyzing the conditions favoring and preventing drug-induced torsades-depointes. Received: 13 August 1997, Returned for revision: 10 September 1997, Revision received: 29 September 1997, Accepted: 22 October 1997     

Blockade of A1 adenosine receptors prevents the ischaemia-induced sensitisation of adenylyl cyclase: evidence for a protein kinase C-mediated pathway

Objective: Acute myocardial ischaemia leads to a transient sensitisation of adenylyl cyclase which may contribute to the occurrence of malignant arrhythmias and the propagation of myocardial necrosis. It is prevented by blockade of protein kinase C (PKC) which is activated in early ischaemia as shown by its translocation from the cytosol to the plasma membranes. Translocation of PKC may also occur in ischaemic preconditioning, a process thought to be induced by activation of adenosine A₁ receptors. In this study it was investigated whether A₁ adenosine receptors may be involved in the sensitisation of adenylyl cyclase and the activation of PKC induced by ischaemia. Methods:Isolated rat hearts were perfused with the specific A₁ adenosine antagonist 8-caclopentyl-1,3-dipropylxanthine (DPCPX, 1 μM) or adenosine (1 μM) prior to ischaemia induced by stop of perfusion for 5 and 10 min. Adenylyl cyclase activity was determined in plasma membranes stimulated by forskolin or stimulated via β-receptors by isoproterenol. Total PKC activity was measured in purified plasma membranes and in the cytosolic fraction using histone III-S as a substrate. Results:Myocardial ischaemia induced a β-receptor-independent sensitisation of adenylyl cyclase (forskolin-stimulated activity 515 ± 55 vs. 384 ± 30 pmol/min/mg protein) which was completely blocked by pre-perfusion with DPCPX (385 ± 23 vs. 386 ± 24 pmol/min/mg protein). DPCPX alone did not alter the responsiveness of adenylyl cyclase to stimulation. The stimulated adenylyl cyclase activity was increased by 20% after pre-perfusion with adenosine, mimicking the ischaemia-induced sensitisation. The effect of adenosine was not augmented by additional ischaemia. PKC activity was translocated from the cytosol to the plasma membranes by acute ischaemia, indicating an activation of the enzyme. This effect was completely abolished by DPCPX. Conclusion: These data demonstrate that in the rat heart the sensitisation of adenylyl cyclase in acute myocardial ischaemia is dependent on activation of A₁ adenosine receptors. It is suggested that the sensitisation of adenylyl cyclase by adenosine or ischaemia might be mediated by an activation of PKC. Received: 23 October 1998, Returned for revision: 19 November 1998, Revision received: 8 February 1999, Accepted: 22 February 1999     

A new rat model of small vessel stenting

Objectives: Restenosis is the major complication of coronary angioplasty and stenting. In addition, the small vessel diameter represents a major limitation to the wide use of the technology. The aim of this study was to assess the feasibility and the vascular response of stent deployment in rat small vessels. Methods: In 40 Wistar rats (500–550 g) a Nir stent crimped on a 1.5 mm Comet angioplasty balloon catheter was deployed at high pressure in the common carotid artery. Neointimal area, neointima/media ratio and the arterial dimension were assessed immediately and at 7, 14, 21, and 28 days after stenting. Results: After stent deployment, the neointimal area and the neointima/media ratio increased progressively and peaked at 14 days (p < 0.05 vs 0 and 7 days). Alpha-actin-positive cells were found circumferentially organized on the lumen surface. At 21 and 28 days after stenting, the neointima and the neointima/media ratio were not statistically different compared with the results obtained fourteen days after stent deployment. No significant differences in the area of external elastic lamina were observed during the study period. In contrast, the internal lumen area was reduced significantly at 14, 21, and 28 days after the stent deployment. Subacute thrombosis rate after stent implantation was 26.5%. Conclusions: The results of this study demonstrated that the balloon expandable stents can be safely placed into rat arteries and the reduction of the internal arterial lumen observed after stent deployment was only due to the neointima formation whereas remodeling did not occur. Received: 5 August 1999, Returned for 1. revision: 6 October 1999, 1. Revision received: 23 November 1999, Returned for 2. revision: 7 December 1999, 2. Revision received: 22 December 1999, Accepted: 6 January 2000     

Antioxidant properties of acetaminophen and cardioprotection

The acute administration of acetaminophen to isolated, perfused guinea pig hearts appears to have cardioprotective effects against the injury/mechanical dysfunction caused by global, low-flow, myocardial ischemia and reperfusion. In the current study we selected ischemia/reperfusion and administration of sodium pentobarbital as perturbations of the electrical stability of the myocardium. We investigated their ability to induce ventricular arrhythmias and changes in the characteristics of monophasic action potentials in the absence and presence of acetaminophen (0.35 mmol/l). The numbers of ventricular premature beats and ventricular salvos encountered in the presence of pentobarbital were significantly (P < 0.05) reduced by acetaminophen. The combined frequency of these arrhythmias was 0.14 ± 0.06/min vs 0.03 ± 0.01/min (P < 0.05) in the absence and presence of acetaminophen, respectively. The incidence of ventricular salvos increased steadily in vehicle-treated hearts after administration of pentobarbital. No such trend was seen with acetaminophen. After 10 min of global, low-flow myocardial ischemia, MAP50 and MAP90 (monophasic action potentials at 50 and 90 % repolarization, respectively) decreased without acetaminophen (e.g. MAP50, 31 ± 4 ms) but did not change during the same time interval with acetaminophen (e.g. MAP50, 57 ± 6 ms)(P < 0.05). During ischemia and reperfusion, acetaminophen attenuated the release of hydroxyl radicals and peroxynitrite. Collectively these data reveal cardioprotective, antioxidant behavior of acetaminophen. Under selected conditions (e.g. those causing release of free radicals and other oxidants) such behavior might also prevent ventricular arrhythmias. Received: 30 October 2000, Returned for 1. revision: 20 November 2000, 1. Revision received: 12 December 2000, Returned for 2. revision: 2 January 2001, 2. Revision received: 14 January 2001, Accepted: 31 January 2001