Sustained macroreentrant ventricular tachycardia

Arrhythmogenesis by single ectopic beats originating in the Purkinje system

Cells in the Purkinje system (PS) are known to be more vulnerable than ventricular myocytes to secondary excitations during the action potential (AP) plateau or repolarization phases, known as early afterdepolarizations (EADs). Since myocytes have a lower intrinsic AP duration than the PS cells to which they are coupled, EADs occurring in distal branches of the PS are more likely to result in propagating ectopic beats. In this study, we use a computer model of the rabbit ventricles and PS to investigate the consequences of EADs occurring at different times and places in the cardiac conduction system. We quantify the role of tissue conductivity and excitability, as well as interaction with sinus excitation, in determining whether an EAD-induced ectopic beat will establish reentrant activity. We demonstrate how a single ectopic beat arising from an EAD in the distal PS can give rise to reentrant arrhythmia; in contrast, EADs in the proximal PS were unable to initiate reentry. Clinical studies have established the PS as a potential substrate for reentry, but the underlying mechanisms of these types of disorder are not well understood, nor are conditions leading to their development clearly defined; this work provides new insights into the role of the PS in such circumstances. Our findings indicate that simulated EADs in the distal PS can induce premature beats, which can lead to the tachycardias involving the conduction system due to interactions with sinus activity or impaired myocardial conduction velocity.

Progression to complete atrioventricular block in a patient with bundle branch re-entry tachycardia

A 38-year-old man with no significant structural heart disease suffered from one episode of wide QRS tachycardia. The electrocardiogram showed a PR interval of 0.20 second and a QRS duration of 0.10 second. His bundle recording revealed an HV interval of 90-100 ms. The tachycardia was inducible with programmed stimulation and displayed a QRS morphology of complete left bundle branch block. It was characterized by an atrioventricular dissociation, a cycle length of 280 ms, and an H deflection preceding each QRS complex. Pacing from the right ventricular apex at a cycle length of 270 ms entrained the tachycardia, while at a cycle length of 260 ms, the tachycardia was terminated. Four years later, the patient presented with complete atrioventricular block with a wide QRS escape rhythm. An electrophysiologic study conducted while he was in 1:1 atrioventricular conduction showed an HV interval of 100 ms. Second-degree infrahisian block developed at an atrial paced cycle length of 700 ms. There was no induction of tachycardia with programmed stimulation before or after isoproterenol. The patient was treated with an implantation of a permanent pacemaker.

Bundle-branch reentry tachycardia

A 21-year-old man with aborted sudden death developed bundle-branch reentry tachycardia at electrophysiologic study. Ablation of the right bundle branch was performed in an attempt to eliminate the recurrence of ventricular arrhythmia. The clinical arrhythmia was no longer inducible; however, a second type of ventricular tachycardia of a different mechanism and origin was induced. Following a new clinical episode of ventricular tachycardia with hemodynamic deterioration, an automatic implantable cardioverter and defibrillator was implanted.

Bundle branch reentry: a mechanism of ventricular tachycardia in the absence of myocardial or valvular dysfunction

OBJECTIVES

The aim of this study was to present bundle branch reentry as the mechanism of sustained ventricular tachycardia in the absence of myocardial or valvular dysfunction.

BACKGROUND

Previous reports have documented the relation between structural heart disease and bundle branch reentrant ventricular tachycardia. Myocardial or valvular dysfunction has thus far been recognized as the only anatomic substrate for the development of this tachycardia.

METHODS

Three patients with a wide QRS complex tachycardia underwent noninvasive and invasive cardiac evaluation and electrophysiologic studies to identify the substrate and mechanism of tachycardia. Catheter ablation of the right bundle branch using radiofrequency current was performed in each patient.

RESULTS

The patients were all men (aged 54, 34 and 72 years) who presented with presyncope, palpitation and cardiac arrest, respectively. Electrocardiography during sinus rhythm revealed nonspecific intraventricular conduction delay in all three patients. Cardiac evaluation revealed no evidence of myocardial or valvular dysfunction in any patient. The baseline HV interval was prolonged in each patient (90, 100 and 75 ms, respectively). Programmed right ventricular stimulation initiated bundle branch reentrant tachycardia with typical left (three patients) and right (one patient) bundle branch block pattern. Catheter ablation of the right bundle branch using radiofrequency current abolished bundle branch reentry in all three patients. After 26-, 13- and 8-month follow-up periods, complete right bundle branch block persisted, and all three patients remained asymptomatic without antiarrhythmic drugs.

CONCLUSIONS

Sustained bundle branch reentry can be a clinical arrhythmia in patients with no identifiable myocardial or valvular dysfunction except for isolated conduction abnormalities in the His-Purkinje system. This mechanism of tachycardia should be recognized during electrophysiologic evaluation, given the seriousness of this arrhythmia and the availability of the effective treatment.

Inadvertent catheter-induced right bundle branch block in a patient with preexistent left bundle branch block and recurrent macroreentrant ventricular tachycardia

This article describes the inadvertent, catheter-induced induction of right bundle branch block resulting not only in transient complete infra-His heart block but also in temporary interruption of the macroreentry circuit of ventricular tachycardia. A patient with preexistent left bundle branch block and spontaneous ventricular tachycardia based upon the bundle branch reentry mechanism underwent electrophysiological testing for the evaluation of sotalol drug efficacy. In search of an optimal His-bundle recording, the manipulation of a 6 Fr quadripolar catheter caused a right bundle branch block, thus advancing the preexistent left bundle branch block to complete heart block. Retrograde ventriculoatrial conduction remained unaffected. The macroreentrant tachycardia with left bundle branch block configuration was no longer inducible. While the patient continued on unchanged sotalol medication (320 mg/d) he required temporary pacing for 16 hours until the block subsided. A subsequent induction attempt demonstrated initiation of the tachycardia. Finally, guided by invasive testing, the patient successfully received amiodarone therapy (300 mg/d). The patient completed an uneventful follow up of 27 months. No progression of conduction delay was observed. This case suggests that the inadvertent induction of right bundle branch block prevents the initiation of ventricular tachycardias relying on bundle branch reentry. Therefore, missed diagnosis or misinterpretation of antiarrhythmic drug efficacy might occur if there is no electrophysiological reevaluation after right bundle branch recovery.

Sustained bundle branch reentry as a mechanism of clinical tachycardia

The incidence of sustained bundle branch reentrant (BBR) tachycardia as a clinical or induced arrhythmia or both continues to be underreported. At our institution, BBR has been the underlying mechanism of sustained monomorphic ventricular tachycardia in approximately 6% of patients, whereas mechanisms unrelated to BBR were the cause in the rest. Data gathered from 20 consecutive patients showed electrophysiologic characteristics that suggest this possibility. These include induction of sustained monomorphic tachycardia with typical left or right bundle branch block morphology or both and atrioventricular dissociation or ventriculoatrial block. On intracardiac electrograms, all previously published criteria for BBR were fulfilled, and in addition, whenever there was a change in the cycle length of tachycardia, the His to His cycle length variation produced similar changes in ventricular activation during subsequent complexes with no relation to the preceding ventricular activation cycles. Compared with patients with ventricular tachycardia due to mechanisms unrelated to BBR, patients with BBR had frequent combination of nonspecific intraventricular conduction defects and prolonged HV intervals (100% vs. 11%, p less than 0.001). When this combination was associated with a tachycardia showing a left bundle branch block pattern, BBR accounted for the majority compared with mechanisms unrelated to BBR (73% vs. 27%, p less than 0.01). The above finding in patients with dilated cardiomyopathy should raise the suspicion of sustained BBR because dilated cardiomyopathy was observed in 95% of the patients with BBR. Twelve of the 20 patients were treated with antiarrhythmic agents, and the other eight were managed by selective catheter ablation of the right bundle branch with electrical energy. Our data suggest that sustained BBR is not an uncommon mechanism of tachycardia; it can be induced readily in the laboratory and is amendable to catheter ablation by the very nature of its circuit. The clinical and electrophysiologic features outlined in this study should enable one to correctly diagnose this important arrhythmia.

Transcatheter electrical ablation of right bundle branch. A method of treating macroreentrant ventricular tachycardia attributed to bundle branch reentry

The present study describes the clinical and electrophysiological characteristics of sustained bundle branch reentrant ventricular tachycardia treated with electrical ablation of the right bundle branch. Seven patients presented with syncopal episodes, and six of the seven had documented episodes of ventricular tachycardia. All patients had depressed left ventricular ejection fraction with cardiomegaly. Six of the seven had dilated cardiomyopathy in the absence of significant coronary disease. Twelve-lead electrocardiograms in all seven patients during sinus rhythm were remarkably similar; six demonstrated intraventricular conduction defect resembling left bundle branch block, and one showed left anterior fascicular block. All patients showed prolonged His-to-ventricle intervals during sinus rhythm. Sustained ventricular tachycardia (with atrioventricular dissociation) because of bundle branch reentry was induced in all patients during baseline electrophysiological study. The His-to-ventricle intervals during tachycardia were similar to those seen during sinus rhythm. Electrical ablation of the right bundle branch was accomplished in each patient with delivery of two electrical shocks (170-310 J) through electrode catheters. Right bundle branch block developed on their surface electrocardiogram immediately after the ablation. Follow-up electrophysiological studies showed no inducible ventricular tachycardia. Clinical follow-up showed no recurrence of syncope or ventricular tachycardia. From the data presented, the following can be concluded. First, right bundle branch ablation is a safe and promising means of treating ventricular tachycardia because of bundle branch reentry and can obviate the need for antiarrhythmic drug therapy and its frequent undesirable side effects. Second, there are common clinical and electrophysiological characteristics that are frequently seen in patients with this tachycardia, and the recognition of these common characteristics should alert the physician to a bundle branch reentrant mechanism of ventricular tachycardia.

Pattern of endocardial activation during sustained ventricular tachycardia

Fifty-five patients with sustained ventricular tachycardia due to prior myocardial infarction underwent intraoperative endocardial activation mapping during ventricular tachycardia to guide subendocardial resection. The mapping data were analyzed to determine the pattern of endocardial activation during tachycardia. Of a total of 122 tachycardias, 101 had a pattern of activation assigned: in 90 (90%), endocardial activation spread centrifugally from a tachycardia site of origin, and 11 (10%) had a continuous loop of electrical activity around an aneurysm. All patients had at least one tachycardia having the centrifugal spread pattern. Tachycardias with a continuous loop pattern had a shorter mean cycle length than those with a centrifugal spread pattern (260 +/- 33 versus 338 +/- 81 ms, p less than 0.002) and a longer duration of endocardial activation relative to the tachycardia cycle length (100 +/- 0 versus 58 +/- 19%, p less than 0.001). There was no difference in preoperative patient characteristics, operative survival or cure of tachycardia between patients having any tachycardias of the continuous loop pattern and those having only centrifugal spread tachycardias. Thus, the vast majority of ventricular tachycardias in this group of patients are characterized by a centrifugal spread of endocardial activation from a site of origin less than 6 cm2 in size. Mapping-guided ablative surgery may remove the entire tachycardia circuit in these patients and a critical portion of the circuit in the minority of patients with continuous loop tachycardias.

Rapid ventricular tachycardia due to His-Purkinje reentry

Two patients developed rapid His-Purkinje reentrant tachycardia during programmed ventricular stimulation for evaluation of recurrent ventricular tachycardia. In Patient 1, His-Purkinje reentry induced a morphologically distinct ventricular tachycardia which may have been a reentrant circuit operating independently for several cardiac cycles. His-Purkinje reentry was not inducible in Patient 2 until lidocaine was given. Following lidocaine administration, sustained His-Purkinje reentrant tachycardia was initiated by 2 premature ventricular stimuli. The tachycardia was rapid (240 beats per minute) and required cardioversion.