Ventricular Tachyarrhythmias
abstract & commentary
Synopsis: Induction of sustained ventricular tachycardia at EP study is a strong predictor of risk in patients with impaired left ventricular function and unexplained syncope. Treatment is recommended with ICD therapy.
Source: Andrews NP, et al. J Am Coll Cardiol 1999;34: 2023-2030.
In this report, andrews and colleagues describe a retrospective case-controlled study on the use of electrophysiologic (EP) testing and implantable cardioverter defibrillators (ICDs) in patients with unexplained syncope. Patients who received an ICD that stored RR intervals and or electrograms from events were identified from a register maintained at Andrew et al’s institution. Thirty of 175 patients who received an ICD before January 1, 1996, had a history of unexplained syncope and inducible ventricular tachycardia, but no documented sustained ventricular tachyarrhythmia. Patients who received antiarrhythmic drug therapy either at the time of their clinical event, at the time of EP study, or during follow-up were excluded. Patients who did not have inducible ventricular tachycardia at their initial EP study were also excluded. The final study group consisted of 22 patients with unexplained syncope and 32 control subjects. The EP studies in both groups were performed using standard techniques. The required definition for an inducible ventricular tachyarrhythmia was the induction of sustained monomorphic ventricular tachycardia by £ 3 ventricular extrastimuli or induction of sustained ventricular flutter or fibrillation by £ 2 ventricular extrastimuli. Electrograms or RR interval logs were analyzed to classify therapy as appropriate or inappropriate. The primary end point was time to first appropriate ICD therapy.
The mean age for both groups was in the late 60s with an 80% male predominance. Eighty-seven percent had coronary artery disease (CAD). Eleven of 22 patients in the syncope group but only eight of 32 in the control group had nonsustained ventricular tachycardia documented by monitoring. Congestive heart failure was also more common in the syncope group (64% vs 34%). Electrophysiologic findings were similar between the two groups. Monomorphic ventricular tachycardia was induced in 86% of the syncope group and 94% of the control group. The cycle length of the induced tachycardia was slightly shorter in the syncope group (256 ± 7 msec vs 282 ± 7 msec; P = 0.047). During follow-up, there was no difference between time to first defibrillator therapy between the syncope and control groups. After 12 months, 57% of the syncope patients and 50% of the control group had an appropriate defibrillator therapy. During all of follow-up, 14 of the 22 patients with syncope had ventricular tachycardia detected and treated by the ICD. Two patients in the syncope group had recurrent symptoms not associated with a tachycardia detected by the ICD. One of these patients also had an appropriate ICD discharge. There were three cardiac transplantations and seven deaths among the 22 syncope patients and two transplants and five deaths among the control subjects.
Andrews et al conclude that induction of sustained ventricular tachycardia at EP study is a strong predictor of risk in patients with impaired left ventricular function and unexplained syncope. They recommend treatment of these patients with ICD therapy.
Comment by John P. DiMarco, MD, PhD
Syncope remains one of the most difficult clinical conditions faced by physicians. By definition, syncope is a transient event and the patients are usually asymptomatic by the time they present for evaluation. As a result, workup of patients with syncope is often frustrating and cost-ineffective. However, since some causes of syncope are potentially fatal should they recur, an aggressive diagnostic approach is usually advocated for high-risk patients.
This paper deals with the outcome of patients with syncope and inducible ventricular tachycardia. It does show that the patients in this series who received an ICD had a high frequency of arrhythmias and also cardiac transplantation and nonsudden cardiac death. In fact, they had higher rates for these three events than were seen in the control group, in which sustained venicular tachycardia was the initial complaint. The question still remains whether the EP study was helpful in defining these patients. In order to know that, we would have to have data on all patients with recurrent syncope evaluated by Andrews et al. In particular, we would like to know the long-term outcomes of patients with similar baseline clinical characteristics who had negative EP studies. Several clinical variables suggest that the syncope group in this study was an unusual population. Fifty percent had nonsustained VT, 27% had class III or class IV heart failure, and 45% had bundle branch block. These proportions are all higher than were seen in the control group. Even with ICD therapy, the syncope group had only a 52 ± 11% 36 months survival without transplant.
Recent preliminary data from the Multicenter Unsustained Tachycardia trial presented at the 1999 American Heart Association meeting indicated that patients with heart failure and nonsustained VT were at high risk for arrhythmic events and nonarrhythmic cardiac death even if they had a negative EP study. Induction of sustained ventricular tachycardia using the same criteria as in this paper was a risk factor, but inducibility did not clearly distinguish high- and low-risk groups. Preliminary data from an Antiarrhythmics Versus Implantable Defibrillators (AVID) trial substudy also show little difference in outcome based on EP test results. Therefore, I believe that there has been an over-reliance on the use of EP studies in patients with syncope. We must admit that the results of EP testing do not provide a certain diagnosis for the cause of a prior event. They may help assess risk for various future arrhythmias. Choice of therapy requires a careful assessment of the entire clinical scenario. ICD therapy will often be the most attractive option for patients with left ventricular dysfunction and unexplained syncope when no other obvious causes have been identified whether they have inducible VT. Guidelines for ICD implantation in patients may have to change in view of these recent findings.
Placement of an ICD may be appropriate for patients with:
a. unexplained syncope.
b. vasovagal syncope.
c. syncope and ischemic heart disease.
d. syncope and LV dysfunction.
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