The effect of atrial stretching on the genesis of atrial arrhythmias was studied in 26 dogs. Left atrial dilatation was produced by inflation of a balloon catheter. Electrophysiological studies were performed by programmed electrical stimulation of the atrium and ventricle. The irritability of the atrium markedly increased when it was distended and atrial arrhythmias (sustained or non-sustained atrial tachyarrhythmias) could regularly be induced by administration of an early extrastimulus or--more rarely--by atrial burst pacing. In 10 cases spontaneous atrial tachycardia appeared during atrial balloon dilatation. The atrial effective refractory period shortened and the atrial conduction time lengthened on atrial stretching, while other electrical variables (cycle length, sinus node recovery time, atrioventricular conduction time, intraventricular conduction, ventricular refractory period, QT interval) remained unchanged. Atrial balloon dilatation was not accompanied by marked haemodynamic changes, and the left ventricular pressure curve, the contractility of the left ventricle and the central venous pressure did not change significantly on atrial stretching. The experimental data suggest that the atrial dilatation plays an important part in the pathogenesis of atrial arrhythmias.

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The development of ventricular tachyarrhythmias caused by low-dose intracoronary infusion of endothelin-1 (ET-1) has recently been observed in dogs. The aim of the present study was to investigate the pathomechanism of ET-1-induced ventricular arrhythmias in 32 anesthetized, open-chest mongrel dogs in group A (n = 14) without, in group B (n = 14), and in group C (n = 4 control) with atrioventricular node ablation. The coronary blood flow (CBF) was measured in the left anterior descending (LAD) coronary artery by an electromagnetic flowmeter. Standard ECG, atrial and ventricular electrograms, and in groups B and C endocardial and epicardial monophasic action potentials (MAPs) were recorded. ET-1 was administered into the LAD at a low dose (30-60 pmol/min). At the time of the appearance of premature beats, CBF was only slightly decreased. The effective ventricular refractory period did not change significantly. Onset of spontaneous polymorphic and monomorphic sustained ventricular tachycardia (sVT) was observed in five dogs without bradycardia and in nine dogs with bradycardia. VTs in dogs with complete AV block were longer and slower. In most of the cases, ventricular fibrillation occurred. ET-1 treatment resulted in a significant increase in MAP 90% duration (255 +/- 9 vs. 290 +/- 8 ms endocardial, 244 +/- 10 vs. 292 +/- 12 epicardial; p < 0.05) at 70 beats/min ventricular pacing. In eight cases (group B), third-phase early afterdepolarization could be recorded. According to our results, the mechanism of ET-1-induced arrhythmias appears to be based on prolongation of MAP duration and development of afterdepolarizations.

The coexistence of congenital complete heart block and QT prolongation represents a special type of arrhythmia. The electrophysiological and clinical characteristics of this syndrome were studied in eight patients suffering from congenital AV block and QT prolongation. Data from 22 patients suffering from congenital complete heart block only, served as a control. In the study group, the appearance of a torsade de pointes type of ventricular tachycardia could regularly be observed and the tachycardial attack could usually be provoked by ventricular extrastimuli. The corrected QT time was markedly prolonged; on ventricular stimulation, at higher pacing rates the QT interval shortened, but remained significantly higher than in the control group. Syncopal attacks--with the character of polymorphic tachycardia--appeared in each patient of the study group while occurring in only three patients from the control group. Patients were given pacemaker implants (using a higher pacing rate) and long-term administration of beta-receptor blockers. The outcome was favourable; no ventricular tachycardia or syncopal attack was observed in the follow-up period.

Ž. Objectives: Recently, extremely high levels of endothelin-1 ET-1 were detected in the pericardial fluid of patients with heart disease; however, the pathophysiological importance of this finding is not known. The present study was designed to characterize ET-1 levels in canine pericardial fluid and to investigate the effects of local high concentrations of exogenous ET-1 in vivo. Methods: In Ž y1 y1. anesthetized, open-chest dogs ET-1 Groups 1 and 2: 11 and 33 pmol P kg P min ; n s 6 and 6, respectively or physiological saline Ž . Group 3, n s 5 were infused into the closed pericardial sac for 40 min. In serial pericardial fluid and aortic blood plasma samples, ET-1 Ž . levels were measured by radioimmunoassay, and analysed by high-performance liquid chromatography HPLC . Systemic arterial blood Ž . Ž . pressure, heart rate, cardiac output CO , standard ECG and right ventricular endocardial monophasic action potentials MAPs were Ž recorded. Results: Basal pericardial fluid ET-1 levels were significantly higher than respective plasma levels 342 " 210 vs. 8.0 " 5.2 pmol P l y1 , n s 14, P -0.001. In HPLC analysis pericardial fluid ET-1 was indistinguishable from ET-1 . Infusion of exogenous 1 -21 ET-1 into the pericardial space induced ventricular arrhythmias in all instances, which were associated with 9.7-fold increase in pericardial fluid ET-1 levels. Ventricular tachycardias developed in 9 of 12 animals. The arrhythmogenic effect of ET-1 was more Ž apparent in dogs with the larger dose. Before the onset of arrhythmias, intrapericardial infusion of ET-1 increased QT time Group 1: . Ž 207 " 18 to 230 " 23 ms, P -0.01; Group 2: 220 " 12 to 277 " 17 ms, P -0.01 and MAP duration at 90% repolarization at 300 ms . Ž . cycle length Group 1: 192 " 9 to 216 " 9 ms, P -0.01; Group 2: 205 " 9 to 255 " 9 ms, P -0.001 . Hemodynamic variables did not change significantly prior to the onset of ventricular tachyarrhythmias. In Group 3, arrhythmias were not observed and all electrophysiological and hemodynamic parameters remained unchanged. Conclusions: Administration of exogenous ET-1 into the pericardial space induces ventricular arrhythmias associated with prolongation of QT time and MAP duration. Whether pericardial fluid ET-1 under pathophysiological conditions can ever reach sufficiently high levels to induce ventricular arrhythmias remains to be elucidated. q 1998 Elsevier Science B.V. All rights reserved.

Earlier studies have shown that hyaluronidase exerts a potent influence upon the lymphatic system of the myocardium and that it reduces the size of myocardial infarcts after coronary occlusion. In this study we compared, in mongrel dogs, the effect of intravenous hyaluronidase or CLS 2210 upon the cardiac lymphatic vessels. We observed that in CLS 2210-treated animals the number of visualized cardiac lymphatic vessels was significantly higher than in the hyaluronidase-treated control group. We have previously demonstrated a cardioprotective effect of hyaluronidase in the treatment of acute myocardial infarction. The present experimental data indicate that intravenous CLS 2210 may have a definite role in the management of acute coronary occlusion. Further studies are needed to confirm these preliminary findings.

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