Influence of Different Conditioning Methods on Force and Fatigue Resistance in Chronically Stimulated Skeletal Muscles

A study was undertaken to compare different conditioning methods for the transformation of latissimus dorsi muscle into a fatigue resistant one for application in circulatory assist. In ten sheep four electrodes were sutured to the epineurium of the left thoracodorsal nerve for indirect electrical stimulation of the latissimus dorsi muscle. In six sheep a "carousel stimulation, " a special multichannel stimulation, in combination with a recently developed conditioning protocol was used for muscle conditioning ( multichannel method ). In four sheep, a conventional stimulation protocol using single channel stimulation was applied for transformation of the muscle (single channel method). The final experiments were carried out when fatigue resistance was obtained. The maximum tetanic forces at different preloads were determined and fatigue resistance was tested during 20 minutes of continuous stimulation. Both conditioning patterns led to fatigue-free chronic stimulation. Muscles conditioned by multichannel stimulation exhibited between 20% and 33% less force than the contralateral unconditioned muscles, whereas in the single channel group this loss was between 32% and 43%. Thus, the multichannel method revealed relatively superior in preserving muscle force for chronic stimulation.     

The Left Subclavian Vein as an Alternative Site for Implantation of the Second Defibrillation Lead

The optimal placement for the second defibrillation lead in a twolead system has never been addressed. We retrospectively reviewed the data of 33 patients with an average age of 59.2 years (range 41–78 years), predominantly mala (n = 29), who underwent implantation of a cardioverter defibrillator (ICD) for treatment of ventricular tachycardia (n = 19) or ventricular fibrillation (n = 14). In all patients an attempt was made to implant an endovenous ICD device (leads only, no subcutaneous patch). In group I (n = 18) the defibrillation anode, a separate unipolar lead, was placed in the common position, the superior vena cava. In group II (n =15) the lead was placed in the left subclavian vein. At least two consecutive shocks reverting ventricular fibrillation at energies ±24J were required for implantation of the ICD device. All shocks were monophasic. The success rate of endovenous defibrillation was significantly higher in group II than in group I (67% vs 28%, P < 0.05). Thus, it could be demonstrated that the position of the defibrillation anode can influence the defibrillation efficacy in transvenous ICD systems. Prospective randomized trials are needed to investigate the optimal position for the second defibrillation electrode, which may gain increasing importance as soon as dual chamber ICDs become available.     

Choosing the Stimulation Rate in Patients with Intermittent Bradycardia and a Single Lead Pacemaker

In order to assess the prevalence of intermittent bradycardia in a pacemaker population, we retrospectively evaluated the occurrence of intrinsic heart activity in 229 patients with ventricular pacing. Spontaneous heart activity was recorded in 60% of the patients. However, the stimulation rate had been decreased in onJy 40% of the patients in order to allow for longer periods of intrinsic heart activity. In the second part of the study we prospectively assessed differences in pacemaker utilization in 19 patients with intermittent bradycardia and single lead pacemakers. All patients were observed over four periods of 14 days, with the following pacing modes: 70 heats/min, 50 beats/min, hysteresis sensing 50 beats/min, and pacing 70 heats/min; and search hysteresis sensing 50 beats/min and pacing 70 beats/min. Search hysteresis pacing is a new feature that theoretically allows for a shorter time of pacing than that of hysteresis pacing. A reduction in the stimulation rate from 70 beats/min to 50 beats/ min resulted in a 60% reduction in pacemaker utilization (P < 0.05). Search hysteresis decreased pacemaker utilization by 33% (P < 0.05) There was no statistical difference between conventional hysteresis and fixed rate pacing at 70 beats/min. Most patients found fixed rate pacing preferable to hysteresis pacing. In order to minimize battery consumption and to avoid unfavorable hemodynamics in patients with ventricular pacing, the stimulation mode and rate should be optimized in patients with intermittent bradycardia to allow for longer periods of intrinsic heart activity.     

The renin-angiotensin system during converting enzyme inhibition with captopril in patients with severe treatment-resistant hypertension

Abstract. The effect of captopril on blood pressure (BP) and various components of the renin-angiotensin system was assessed in ten severely hypertensive patients. Captopril acutely reduced the BP with a maximum decrease of 23% at 90–120 min.
Maintenance treatment with captopril alone could not control the BP in any of the patients. Addition of hydrochlorothiazide markedly reduced the BP, while supplementation with propranolol caused no consistent changes.
Three patients attained a supine diastolic blood pressure (SDBP) ≤90 mmHg. Only two patients had a fall in SDBP less than 10 mmHg. One patient stopped because of taste disturbances.
Monitoring the renin-angiotensin system showed suppressed plasma concentrations of angiotensin II and increased levels of angiotensin I and renin, indicating the inhibition of converting enzyme activity. Plasma concentration of renin substrate decreased significantly. This observation has important implications for the methodology of renin assays.
Captropril is an effective alternative in the treatment of hypertensive patients not readily controlled with conventional therapy.     

Pressure‐Guided Cryoballoon Isolation of the Pulmonary Veins for the Treatment of Paroxysmal Atrial Fibrillation

Pressure‐Guided Cryoballoon Pulmonary Vein Isolation. Background: Pulmonary vein (PV) isolation using a balloon‐mounted cryoablation system is a new technology for the percutaneous treatment of atrial fibrillation (AF). Complete PV occlusion during balloon ablation has been shown to predict successful electrical isolation. The aim of this study was to correlate mechanical PV occlusion with changes in a pressure curve recorded at the distal tip of the cryoballoon catheter. Methods and Results: We analyzed 51 PVs in 12 patients (61 ± 6 years old) with paroxysmal AF. At first, PV occlusion via the cryoballoon was documented by changes in the pressure curve. Once the PV is occluded, the pressure curve registered in the vein converts from a left atrial pressure curve to a pulmonary artery pressure curve: the PV wedge curve. Occlusion was then confirmed by transesophageal echocardiography (TEE). Following 2 cryoablation applications, electrical PV isolation was assessed with a circumferential mapping catheter. Under the exclusive guidance of changes in the pressure curve at the tip of the cryoballoon, mechanical occlusion confirmed by TEE was achieved in 47 of 51 PVs (92%). Three PVs required further TEE guidance to achieve occlusion. All 50 occluded veins were electrically isolated after cryoablation. One right inferior vein, which could not be occluded with the balloon, displayed conduction post cryoablation and was isolated by focal ablation. Conclusions: Occlusion and electrical isolation of PVs during cryoballoon ablation can be predicted by the appearance of a PV wedge curve at the tip of the catheter. This new straightforward parameter may facilitate the procedure. (J Cardiovasc Electrophysiol, Vol. 21, pp. 120‐125, February 2010)     

Seroprevalence of pertussis antitoxin (anti‐PT) in Sweden before and 10 years after the introduction of a universal childhood pertussis vaccination program

Hallander HO, Andersson M, Gustafsson L, Ljungman M, Netterlid E. Seroprevalence of pertussis antitoxin (anti‐PT) in Sweden before and 10 years after the introduction of a universal childhood pertussis vaccination program. APMIS 2009; 117: 912–22. The prevalence of IgG ELISA antibodies against pertussis toxin (anti‐PT) was studied in two Swedish seroepidemiological studies. One was performed in 1997 when the new pertussis vaccination program was 1 year old (n = 3420). In 2007, when Pa vaccines had been used countrywide for 10 years in the universal child vaccination program, this study was repeated to analyze the effect of vaccination on anti‐PT prevalence (n = 2379). Before the statistical analysis of seroprevalence, children vaccinated within the last 2 years before the serosurveys were excluded. The results indicate a reduced exposure to Bordetella pertussis in the population. The proportion of sera without measurable anti‐PT antibodies increased significantly, aggregated over all comparable age groups, from 3.8% in people sampled in 1997 to 16.3% in people sampled in 2007. For cord blood, 1% was without measurable anti‐PT antibodies in 1997 compared to a significantly higher level, 12%, in 2007. With anti‐PT concentrations of ≥50 and ≥100 EU/ml as cutoff points for ‘recent infection’ the proportion above the cutoff points for younger children was significantly higher in 1997 than in 2007 at both cutoff points. For all adults, 20 years of age and older, the difference in proportions above the lower cutoff point was close to statistically significant, comparing 1997 with 2007. This was not the case at 100 EU/ml. In the 1997 samples of children, there was a significant downward trend of ‘recent infections’ at both cutoff points for three sampled age groups between 5 and 15 years of age from 21% at 5.0–5.5 years of age to 7% at 14.7–15.7 years for the lowest cutoff. In the 2007 samples of children, on the contrary, there was a significant continuous upward trend of ‘recent infections’, at both cutoff points, for four sampled age groups between 4 and 18 years of age – from 4% at 4–5 years of age to 16% at 17–18 years at the lowest cutoff. The continuous increase, with age of children with high anti‐PT concentrations, supports the recent change in the general Swedish childhood vaccination program to include a pre‐school booster at 5–6 years and a school‐leaving booster at 14–16 years of age.     

Sudden Death in the Community

About one fifth of all deaths occur suddenly and unexpectedly, often as the first manifestation of heart disease. Several tests have been developed during the past 2 decades for risk stratification of such an event, but only a minority of victims can be identified as being at high risk before sudden death occurs. Improving the results of out-of-hospital resuscitation attempts is of crucial importance. Use of the automated external defibrillator is rapidly increasing worldwide. However, the defibrillator must be used within minutes after the onset of cardiac arrest, and rapid recognition and localization of the victim are essential. The development of a device that constantly monitors vital signs and can diagnose cardiac arrest, generate an alarm, and transmit the location of the victim could be an important step in improving the results of cardiac resuscitation. (J Cardiovasc Electrophysiol, Vol. 14, pp. S104-S107, September 2003, Suppl.)     

Body Composition,Intraerythrocyte Sodium Content,Volume Regulation and Blood Pressure during Moderate Sodium Restriction in Hypertensive Men

ABSTRACT. Eleven moderately obese middle-aged male outpatients with untreated mild hypertension reduced their sodium intake by about 120 mmol per day during 4–6 weeks. Diastolic blood pressure was then significantly reduced in comparison with a matched control group. The reduction of urinary sodium excretion was significantly correlated to the change in mean arterial pressure. Mean body mass showed a small significant decrease, although there were no significant changes in total body water or body fat as determined from measurements of ⁴⁰K and tritiated water. Nor did mean extracellular water or plasma volume (Evan's blue) show any significant change. The decrease in urinary sodium excretion was associated with increases in plasma renin activity and urinary aldosterone excretion, while a sympathetic nervous natriuretic index (urinary dopamine to noradrenaline excretion ratio) decreased. The low sodium diet period was followed by a period of energy reduction as well as sodium restriction for 15 weeks. Mean body mass was then reduced by about 8 kg. The systolic but not the diastolic blood pressure showed a significant decrease. The intraerythrocyte content of water, sodium and potassium did not change significantly during any of the diet periods. We conclude that moderate sodium restriction lowered the blood pressure and affected the renin-aldosterone and sympathetic nervous system to retain sodium which might explain the constancy of the plasma volume.