Abstract & Commentary
Synopsis: Ventricular ectopy originating in the distal Purkinje system may be a dominant trigger for initiation of idiopathic ventricular fibrillation.
Source: Haissaguerre M, et al. Circulation. 2002;106: 962-967.
Haissaguerre and colleagues from 6 referral hospitals in Europe and Asia describe electrophysiologic findings in 27 patients with primary idiopathic ventricular fibrillation. All patients had no evidence for structural heart disease after undergoing physical examination, electrocardiograms, echocardiography, cardiac catheterization, and in selected patients, endomyocardial biopsy. Electrocardiographic findings and exercise testing excluded Catecholaminergic polymorphic ventricular tachycardia, long QT syndrome and Brugada syndrome. Twelve patients underwent genetic testing that excluded abnormalities in several cardiac ion channels known to be associated with sudden death. Patients had had recurrent ventricular fibrillation prior to undergoing study and had failed a mean of 3.6 ± 2 antiarrhythmic drugs. Twenty-three of the 27 patients had received an implantable cardioverter defibrillator (ICD) before undergoing study but were referred because of frequent recurrent arrhythmias. Spontaneous arrhythmias were noted during their in-hospital evaluation in 24 of the 27 patients. These patients had 7841 ± 9595 premature ventricular beats per 24 hours. Three patients had no ventricular premature beats during in-hospital recording. During electrophysiologic study, runs of repetitive beats or ventricular fibrillation were initiated with short coupling intervals of extrastimuli in most patients. Similar patterns were seen during spontaneous episodes in those patients in whom they had been recorded.
Two groups of patients were identified. In 4 patients, ventricular premature beats originated in the right ventricular outflow tract. However, in the remaining 23 patients, there was evidence that the premature beats originated from the peripheral Purkinje system. The site of origin for these 23 patients was the right ventricle in 7, the left ventricle in 9, and both ventricles in 4. Purkinje sources were located in the anterior right ventricle or in a wide region of the lower half of the left ventricle. These sites were identified by a high frequency, discrete Purkinje potential that was present both before the QRS during sinus rhythm and before the ventricular premature beats. As is characteristic of ectopy arising from the Purkinje system, the QRS complex was relatively narrow compared to the complexes seen with beats originating from ventricular myocardium.
Most patients had several PVC morphologies. These morphologies were progressively eliminated by ablation at multiple sites guided by the early Purkinje potential before the premature beat. After ablation, the local electrogram showed abolition of the local Purkinje potential and a slight delay in the occurrence of the local ventricular electrogram. In 3 patients without spontaneous arrhythmias during the procedure, paced mapping was used to identify a probable source of the premature beats. If Purkinje potentials were identified at the sites, RF energy was delivered. It was noted during ablation that RF delivery could transiently worsen arrhythmias producing runs of polymorphic ventricular tachycardia or ventricular fibrillation.
After the procedure, 3 patients had a late recurrence of premature beats and were treated with an antiarrhythmic drug. During follow-up, 2 of these patients had recurrence of VF treated by their defibrillators and one patient had presyncope associated with polymorphic ventricular tachycardia. In the remaining patients, Holter recordings showed no or few (28 ± 49) isolated premature beats per 24 hours in the absence of antiarrhythmic drug therapy. In these 24 patients during a follow-up of 24 ± 28 months, there was no sudden death, syncope, or recurrence of VF.
Haissaguerre et al conclude that ventricular ectopy originating in the distal Purkinje system may be a dominant trigger for initiation of idiopathic ventricular fibrillation. Preliminary evidence suggests that radiofrequency ablation of these Purkinje foci may provide protection against recurrence.
Comment by John P. DiMarco, MD, PhD
During the last 30 years, considerable attention has been directed toward the syndrome of patients with structurally normal heart and ventricular fibrillation. Several genetic patterns have been identified including the long QT syndromes, catecholaminergic polymorphic ventricular tachycardia, and the Brugada syndrome. Other causes of ventricular fibrillation in patients with normal hearts may include commotio cordis, coronary spasm, electrolyte abnormalities and drug effects. All of these etiologies were excluded in the patients in this report.
Finding that ectopy in these patients had a site of origin in the distal Purkinje system and that ablation of these sites was associated with intermediate protection against recurrent VF is quite exciting. However, it must be remembered that introduction of extra stimuli during electrophysiologic studies in truly normal individuals should not initiate polymorphic ventricular tachycardia or ventricular fibrillation. Therefore, one must be cautious and not conclude now prematurely that these patients do not have additional abnormalities that will become manifest over time.
In prior studies, the long-term prognosis of patients without structural heart disease who were resuscitated from a cardiac arrest has been favorable compared to the prognosis of patients with advanced structural heart disease. However, since these patients have normal cardiac function, recurrent arrhythmias are truly tragic. The observations in this paper suggest that at least some of these patients may be effectively treated with catheter ablation. However, at the present time, a conservative course using ablation in conjunction with defibrillator implantation seems most reasonable until the long-term natural history of this disorder is better understood.
Dr. DiMarco is Professor of Medicine, Division of Cardiology University of Virginia, Charolettesville.