Antiarrhythmics vs. Implantable Defibrillators (AVID) Registry
May 1, 1999 4 minutes read
Antiarrhythmics vs. Implantable Defibrillators (AVID) Registry
Abstract & Commentary
Synopsis: An analysis of patients who were identified as having significant ventricular arrhythmias but were not randomized in the study showed that the prognosis of patients with all the types of arrhythmias is poor.
Source: Anderson JL, et al. Circulation 1999;99: 1692-1699.
The antiarrhythmics vs. implantable defibrillators (AVID) trial tested the hypothesis that ICD implantation was better than antiarrhythmic drug therapy in selected survivors of sustained ventricular tachyarrhythmias. The main data from this trial have been previously reported (N Engl J Med 1997;337:1576-1583). The study showed that there was a significant reduction in total mortality with ICD therapy. This paper also includes an analysis of patients who were identified as having significant ventricular arrhythmias but were not randomized in the study.
During AVID, seven groups of patients were identified as candidates for a registry. The first three groups included patients with primary cardiac arrests due to ventricular fibrillation (VF), documented sustained primary ventricular tachycardia (VT) with syncope, and documented sustained primary VT with hypotension and a low ejection fraction. Only these three groups of patients were eligible for randomization in the main trial. The other groups that could be included in the registry but were not eligible for randomization consisted of patients with the following characteristics: 1) sustained VT with hypotension but an ejection fraction greater than 0.40; 2) hemodynamically stable VT; 3) sustained VT or cardiac arrest due to what was thought to be a transient or correctable cause; and 4) syncope with structural heart disease and VT or VF inducible at electrophysiologic study.
During the AVID trial, 4595 patients were placed in the AVID registry and 1016 were randomized. The patients in the registry averaged 64 years of age and 77% were male. The mean left ventricular ejection fraction in the registry was 35% and 77% of these patients had evidence of coronary artery disease. Among the patients with arrhythmias who were eligible for randomization, the reasons for not participating in the trial included patient or family refusal (45%), treatment predetermined by referring physician (28%), physician refusal (11.5%), prior amiodarone use (2%), and miscellaneous reasons (13%). There were only minor differences between randomized and nonrandomized patients among the patients eligible for the trial. Mortality in the registry patients was sought through the national death index service. When survival was analyzed by arrhythmia type, it was noted that there was a relatively high rate of mortality for all arrhythmia groupings. Two-year survival rates ranged from 76% in patients with syncopal VT to 84% in patients with unexplained syncope and inducible VT. Survival was also associated with ejection fraction. This was particularly noticeable for patients with asymptomatic VT and transient or correctable causes of VT/VF. For these two diagnoses, two-year survival rates for patients with ejection fractions greater than or equal to 35% and less than 35% were 85.3% vs. 67.7% and 86.1% vs. 70.8%. Anderson and associates conclude that the patients entered into the randomized portion of the trial were representative of all patients with serious ventricular arrhythmias. They also note that the prognosis of patients with all the types of arrhythmias included in the registry is poor.
Comment by John P. DiMarco, MD, PhD
It is always important to know whether the population enrolled into a randomized clinical trial is representative of patients with a similar condition encountered in the community. These data from the AVID trial support our ability to apply the findings of the trial to the general population. It is particularly interesting, however, to note that there was still a high mortality among patients who were not eligible for registry. In particular, patients who have what are usually thought to be transient or correctable causes had a higher mortality than the patients who were eligible for entry into the trial. Too frequently, physicians will ascribe the occurrence of a serious ventricular arrhythmia to some transient complicating factor. However, it may well be that the substrate for the arrhythmia is always there. Multiple triggers may precipitate life-threatening episodes or the same trigger may occur in the future. The advantage of ICD therapy for such patients would be that it will always be there but will remain inactive unless an arrhythmia develops. However, unless there is some irreversible condition, device therapy should still be effective if an episode of VT or VF occurs.
The major limitation with this paper is some degree of uncertainty about the completeness of the registry. Patients with ventricular arrhythmias can present in a number of ways. Also, it is possible that the registry doesn’t reflect the population of patients in the more general medical community. However, the data presented in this paper represent the largest survey of patients with sustained ventricular arrhythmias yet available and should form the basis for estimates made for planning future trials.
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