Post-Resuscitation Ventricular Tachycardia
ABSTRACT & COMMENTARY
Synopsis: Regular, rapid ventricular tachycardia is the most common recurrent arrhythmia noted in patients resuscitated from an initial episode of ventricular fibrillation.
Source: Ruppel R, et al. J Am Coll Cardiol 1998; 32:1724-1730.
Little is known about recurrent arrhythmia events in resuscitated patients. Thus, Ruppel and associates describe their experience in a group of patients who were resuscitated from ventricular fibrillation (VF) unassociated with myocardial infarction and then received implantable cardioverter defibrillators (ICDs) that were capable of storing intracardiac electrograms. Forty patients entered the study between November 1991 and January 1995. Twenty-eight of the patients had coronary artery disease with a mean left ventricular ejection fraction of 38%. Twenty-four of these 28 patients (86%) had a prior myocardial infarction. Four patients had idiopathic VF. Five patients had dilated cardiomyopathy and three patients had other types of cardiac disease with an overall ejection fraction in this group of 42 ± 17%. Patients were eligible for inclusion if they were resuscitated from documented VF that was not related to an associated myocardial infarction, if VF was the only arrhythmia documented, and if they went on to have an ICD capable of intracardiac electrogram recording and storage implanted. Prior to ICD implantation, all patients underwent a baseline electrophysiologic study that used up to three extrastimuli during ventricular pacing at three basic cycle lengths from two right ventricular sites. Patients received a transvenous ICD system using either a Guidant/CPI Ventak P2 or PRX-II/III device. These systems store intracardiac electrograms recorded between the two shock coils on the ICD connected in a bipolar configuration. Patients were discharged from the hospital off all antiarrhythmic drugs. When supraventricular arrhythmias with high ventricular rates occurred, either AV nodal blocking agents were added or AV nodal catheter ablation was performed. Patients were followed up at intervals of every 2-3 months. The ICDs were interrogated and intracardiac electrograms from any therapies delivered were recorded and analyzed. Arrhythmias at the time of therapy were classified as VF, ventricular tachycardia, atrial flutter, atrial fibrillation, or sinus tachycardia.
During a mean follow-up of 23 ± 11 months, seven patients died, with six of the deaths being attributed to congestive heart failure and one death due to carcinoma of the lung. Thirteen of the initial 40 patients (33%) developed recurrent ventricular arrhythmias that were appropriately treated by their ICD. Thirteen patients (33%) also received inappropriate therapies because of either supraventricular arrhythmias or system failures. Three of these latter patients also received inappropriate therapies for ventricular arrhythmias. A repeat episode of VF was uncommon in the series. There were only five episodes of VF observed in two patients. One of these patients had no structural heart disease and the other had a surgically corrected atrial septal defect. In both of these patients, VF was the only arrhythmia documented during follow-up. Eleven patients experienced a total of 36 episodes of monomorphic ventricular tachycardia. In only two of these patients was degeneration of ventricular tachycardia to VF documented. Of these 11 patients, seven had coronary artery disease, three had dilated cardiomyopathy, and one had no structural heart disease. Atrial fibrillation and atrial flutter were the most common reasons for inappropriate therapy. Four of the 40 patients (10%) received inappropriate therapy due to device malfunction or lead displacement.
Age, gender, cardiac diagnosis, and left ventricular ejection fractions failed to distinguish between those with clinical recurrence of ventricular arrhythmias and those without. The data from the baseline electrophysiologic study were also not helpful. At baseline electrophysiologic study, monomorphic ventricular tachycardia was induced in 14 patients and VF in seven patients. No ventricular arrhythmias were inducible in the remaining 19 patients. Five of the 14 patients with ventricular tachycardia induced had spontaneous ventricular tachycardia during follow-up and none had VF. One of the seven patients who had VF at the initial study had VF during follow-up. Six of the 19 patients who had no ventricular arrhythmias induced at the initial study had ventricular tachycardia and one had VF during follow-up. Ruppel et al conclude that regular, rapid ventricular tachycardia is the most common recurrent arrhythmia noted in patients resuscitated from an initial episode of VF and that the ability to predict recurrence of either ventricular tachycardia or VF is limited.
Comment by John P. DiMarco, MD, PhD
This interesting paper is one of the first papers to report on patients resuscitated from cardiac arrest who received ICDs that can store electrograms. The size of this group is relatively small and we will no doubt see more conclusive data from some of the large cardiac arrest trials, such as the antiarrhythmic vs. implantable defibrillators (AVID) or the Canadian Implantable Defibrillator Study (CIDS) that have recently been completed. However, Ruppel et al make several interesting observations. The primary message from this study is the limited role of electrophysiologic studies in the evaluation of out-of-hospital cardiac arrest survivors. Electrophysiologic studies have their greatest sensitivity in patients with fixed arrhythmia substrates, such as prior myocardial infarction and monomorphic tachycardias. In patients who present with VF, the substrate is either less stable or the arrhythmia may be reproducible only under certain physiologic conditions. There are significant implications in this observation in terms of the use of electrophysiologic studies to predict future events. In the Multicenter Automatic Defibrillator Implantation Trial, an inducible ventricular tachycardia at electrophysiologic study was used to identify the high-risk population that subsequently benefited with ICD implantation. We will soon have data from the Multicenter Unsustained Tachycardia Trial to confirm or refute this hypothesis. The latter trial, unlike the former, included three groups: an untreated group of patients who had no inducible arrhythmia, a group of patients who had inducible arrhythmia but were not treated, and a group of treated patients with inducible arrhythmia. If, as seen in this study, results during electrophysiologic study are not good predictors of cardiac arrest, our ability to intervene specifically in high-risk populations with expensive devices such as ICDs will be markedly limited.
It is interesting that only about 33% of the patients in this trial experienced recurrent arrhythmias during follow-up of all antiarrhythmic therapy. In the AVID and CIDS trials, mortality in drug-treated patients was almost as high as the frequency of appropriate shocks reported here. Therefore, one must suspect that either the patient population in this study was somewhat different than the one recruited for those large prospective trials or that drug therapy provides little benefit.
The other interesting finding in this paper is the relatively high frequency of inappropriate therapies. Atrial fibrillation and atrial flutter are common problems in patients with ICDs. The introduction of dual-chamber devices allows better identification of these arrhythmias when they occur and may allow programming that will decrease the frequency of inappropriate shocks. It is also striking that 10% of the patients had shocks related to system failures despite the fact that the median follow-up was only 22 months. Deterioration of the systems, which leads to inappropriate shocks or repeat operations, is likely to be a major factor complicating ICD therapy as patients live longer after implant and as the prophylactic use of ICDs becomes more common.