Comparison of the results of programmed ventricular stimulation from the right ventricular apex and outflow tract: a randomized, prospective study.

OBJECTIVE: The aim of this prospective study was to analyse the yield of programmed ventricular stimulation at the right ventricular apex compared with the outflow tract. METHODS: A stepwise randomized cross-over protocol of programmed ventricular stimulation with alternating stimulation at both sites was used in 66 patients who were studied because of sustained ventricular tachycardia (n = 30), ventricular fibrillation (n = 7), or non-sustained ventricular tachycardia and/or syncope (n = 29). RESULTS: There were no significant differences between the results of stimulation from either right ventricular site with regard to the presence or absence of structural heart disease, spontaneous arrhythmia, ejection fraction or effective refractory periods. Overall, monomorphic ventricular tachycardia was inducible in 33 patients (50%); in 25 patients (75.8%), this arrhythmia was induced from both sites. However, in only 17 of these 25 patients (68%) did the induced monomorphic ventricular tachycardias have the same morphologies and similar (+/- 50 ms) cycle lengths. Ventricular fibrillation was inducible in 11 patients (17%), mostly by three extrastimuli (n = 8; 73%). CONCLUSIONS: (1) stimulation from at least two right ventricular sites is desirable because of their independent contribution to the induction of ventricular tachyarrhythmias, (2) the non-inducibility or inducibility at one ventricular site does not predict the effect at another stimulation site, (3) the effective refractory period at the right ventricular apex and outflow tract do not differ, (4) the inducibility of multiple ventricular tachycardia morphologies emphasizes the importance of documenting the cause of spontaneous arrhythmias with multiple electrocardiographic leads to ensure the correct interpretation of arrhythmias induced by programmed stimulation, (5) clinical or haemodynamic features cannot predict whether one or more stimulation sites will be required for induction of ventricular tachycardia. These results are important for the diagnostic evaluation and assessment of pharmacological or non-pharmacological interventions.

Influence of sympathetic withdrawal on early postinfarction arrhythmias.

In this work we studied the incidence and characteristics of early postinfarction arrhythmias in rabbits with sympathetic denervation. The electrical and haemodynamic changes were analyzed. Three groups of animals submitted to coronary occlusion were studied. A control group of normal animals (I), another group of animals injected with practolol prior to occlusion (5 mg/kg i.v.) (II) and a third group of animals in which stellate ganglia were surgically excised prior to occlusion (III). In the control group incidence of early postinfarction arrhythmias was 60% (12 of 20) while in Groups II and III incidence was only 25% (3 of 12 rabbits). The influence of excision or pharmacological blockade of sympathetic system and their role in the genesis of the early arrhythmias is discussed.

Physical exercise inducing electrophysiological changes in the atria: sympathetic-mediated effects?

Rats were subjected to long-term physical exercise by swimming and their hearts were examined electrophysiologically in order to identify relevant factors as mechanisms of protection from rhythm disturbances. The role of catecholamines was also studied using a chronically applied beta-adrenergic blocking drug, Practolol, or a catecholamine depleting drug, Reserpine. The results were compared with those obtained in rats similarly injected but kept in sedentary life. Action potential duration was found to be prolonged in trained animals regardless of the drug employed. Trained animals showed increments in the myocardial mass. Prolongation of the action potential coincided with lower values for maximum follow frequencies. It is suggested that the effects elicited could protect the heart against rhythm disturbances. The sympathetic nervous system seemed to play no important role.

Effect of hypothalamic ventro-medial nucleus electric stimulation and 6-hydroxydopamine on cardiac lipoprotein lipase activity in rabbits.

The influence of hypothalamic electric stimulation and administration of 6-hydroxydopamine (6-OHDA) on cardiac lipoprotein lipase (LPL) activity was investigated in 19 rabbits either acutely stimulated in the hypothalamic ventro-medial nucleus (HVMN), or injected with 6-OHDA, or submitted to both experimental procedures. 6 animals served as controls. In rabbits pretreated with 6-OHDA a significant decrease of LPL activity was found with respect to controls (p less than 0.005) and also to stimulated animals (p less than 0.005). The possible mechanism underlying this change is discussed.

Influence of parasympathetic pathways on early post--infarction arrhythmias.

The close relation between heart rhythm disorders that follow acute myocardial infarction (MI) and autonomic nervous system activity has come into focus recently. In order to evaluate the influence of the parasympathetic outflow on the incidence and characteristics of the early arrhythmias that follow myocardial infarction, the authors developed an experimental model of MI in rabbits by acute occlusion of the left ventricular artery. They have found that after the acute experimental MI an early stage of rhythm disorders is developed in 60% of the animals. In a second group of animals submitted to vagotomy prior to coronary occlusion none of rabbits exhibited arrhythmias. A third experimental series was performed in animals pretreated with atropine before and during the coronary occlusion; in this group the incidence of arrhythmias was the same as in control animals. The haemodynamic data obtained from the animals pretreated with atropine were similar to those obtained in control animals. The influence of vagal afferent and efferent pathways and their role in the genesis of the early arrhythmias is discussed.

[Role of the autonomic nervous system in early arrhythmias in acute myocardial infarct in the rabbit]. / Influencia del sistema nervioso autónomo sobre las arritmias tempranas en el infarto miocárdico agudo en el conejo.

In order to evaluate the influence of the autonomic nervous system in the incidence and characteristics of the early arrhytmias that follows myocardial infarction, we have developed an experimental myocardial infarction in rabbits by acute occlusion of the left ventricular artery. The influence of adrenergic and cholinergic suppression over rhythm disorders and hemodynamics changes after experimental infarction in the rabbit was also studied. We found that after the acute experimental infarction in the rabbit heart, arose an early stage of rhythm disorders in 60% of the animals. In a group of animals that were injected with Practolol before coronary occlusion, the incidence of arrhythmias was 25% and in a group of animals with vagotomy prior to occlussion none of them developed rhythm disorders. It was concluded that the model is highly steemed for the study of early arrhytmias and that automatic nervous system has an important role in the incidence of such arrhythmias.

Influence of vagal suppression on early arrhythmias following experimental myocardial infarction in dogs.

The close relationship between disturbances of heart rhythm that follow acute myocardial infarction, and the autonomic nervous system is of particular interest. These disturbances have been attributed to the sympathetic and parasympathetic influences upon the heart. The present investigation was undertaken in order to study the influence of parasympathetic suppression on early arrhythmias following acute myocardial infarction in dogs with acute coronary occlusion. Two series were examined: control and vagotomized animals. In vagotomized dogs, the incidence of early post-infarction arrhythmias was 9 per cent against 66 per cent in the control series. The heart rate and blood pressure did not show significant changes in either series. The results emphasize the importance of the afferent and efferent vagal ways in the genesis of early arrhythmias.