(Circulation. 1999;99:1692-1699.)
© 1999 American Heart Association, Inc.
Clinical Investigation and Reports |
From the University of Washington, Seattle.
Correspondence to Alfred P. Hallstrom, PhD, AVID CTC, 1107 NE 45th St, Room 505, Seattle, WA 98105-4689. E-mail avidctc{at}u.washington.edu
| Abstract |
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Methods and ResultsOf 5989 patients screened, 4595 were registered and 1016 were randomized. Mortality follow-up through 1996 was obtained on the 4219 Registry patients enrolled before 1997 through the National Death Index. Crude mortality rates (mean±SD, follow-up, 16.9±11.5 months) were: VF cardiac arrest, 17.0% (n=1399, 238 deaths); Syncopal VT, 21.2% (n=598, 127 deaths); Symptomatic VT, 15.8% (n=1065, 168 deaths); Stable (asymptomatic) VT, 19.7% (n=497, 98 deaths); VT/VF with transient/correctable cause, 17.8% (n=270, 48 deaths); and Unexplained syncope, 12.3% (n=390, 48 deaths).
ConclusionsPatients with seemingly lower-risk or unknown-risk VAs (asymptomatic VT, and VT/VF associated with a transient factor) have a (high) mortality similar to that of higher-risk, AVID-eligible VAs. The similar (and poor) prognosis of most patients with VT/VF suggests the need for reevaluation of a priori risk grouping and raises the question of the appropriate arrhythmia therapy for a broad range of patients.
Key Words: antiarrhythmia agents registries death, sudden fibrillation tachycardia
| Introduction |
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Survivors of ventricular fibrillation (VF) or symptomatic, sustained ventricular tachycardia (VT) represent an important therapeutic target and public health problem1 because of their known high risk of arrhythmia recurrence and sudden death.2 3 Traditional antiarrhythmic drugs have not provided effective prophylaxis against sudden death (even when guided by Holter recordings or electrophysiological studies) and have sometimes been harmful.4 5 6 7 In the past few years, treatment for these patients has consisted mainly of the mixed class II/III agents amiodarone and sotalol or implantable cardioverter-defibrillators (ICDs).8 9 10 11 12 13 14 Randomized trials comparing these therapies are only now being performed and results reported.15 16 17 18 19 20 21 The Antiarrhythmics Versus Implantable Defibrillators (AVID) study was a large, randomized, secondary prevention trial.21 In AVID, ICD therapy was associated with 39%, 27%, and 31% reductions in mortality at 1, 2, and 3 years, respectively, compared with antiarrhythmic drug therapy (mostly empirical amiodarone).
We present here the design and initial observations of the AVID Registry study, performed in parallel with the randomized trial. We confirm preliminary observations that the randomized patients are representative of the general high-risk VT/VF population.22 Finally, we present clinical characteristics and survival for patients thought, at the time of trial design, to be at too low risk for arrhythmia recurrence to be included in the trial.
| Methods |
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Screening classified the index arrhythmia to determine
eligibility for the randomized trial (categories A, B, and C, Figure 1
). Screening also excluded certain
patients from the registry (Figure 2
).
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Generally, only patients with a reasonable likelihood of being eligible to receive antiarrhythmic drug therapy, ICD therapy, or both were included in the AVID Registry. However, patients who experienced out-of-hospital VT or VF thought to be of transient or correctable cause (eg, in conjunction with myocardial infarction, acute ischemia, drug overdose, or severe electrolyte imbalance) were included to evaluate whether their outcome was better than that of the patients with other arrhythmias, as traditionally believed.2
The second step was to complete the AVID Registry form (Appendix 1) for any patient without Registry exclusion. Demographics, baseline data, and trial eligibility (pages 1 and 2) were obtained during screening (trial exclusion criteria are listed under item 8). Page 3 was completed at hospital discharge and covered procedures done after the index arrhythmia, discharge medications, heart rate, blood pressure, creatine kinase MB isoenzyme measurements obtained within 3 days after the index arrhythmia, the date of the index arrhythmia, and the admitting and discharge dates for the screening hospitalization. These 3 pages were sent to the Data Coordinating Center.
The fourth page was used solely for obtaining follow-up information through the National Death Index Service (NDIS).23 Only page 4 related the Registry identification number to specific patient-identifying information, such as name and social security number. To ensure patient confidentiality, page 4 was kept at the local site and the data were not stored at the coordinating center.
Follow-up of the Registry patients was through the NDIS. Each AVID center entered page 4 data on a diskette; these were sent to the NDIS, which conducted a search based on name, social security number, and birth date for matches against routinely assembled vital statistics (ie, mortality). Using the Registry identification number as a link, the results of this search were incorporated into the Registry database. There were 144 registrants (3.1%) without patient identifiers, either because the site did not participate in the Registry follow-up (n=128) or one of the key identifiers was missing (n=16).
This article reports results based on vital status reports through December 31, 1996, and thus is restricted to the 4219 registry patients with patient identifiers whose index arrhythmic event occurred before January 1, 1997. The NDIS search missed 3 of the 162 deaths (1.85%) that occurred in trial patients.
Survival estimates are based on the methods of Kaplan and Meier.24 Comparisons among survival curves were made by the global log-rank test.25 No differences were noted between analyses of all sites and analyses restricted to centers with relatively large numbers of registrants; thus, analyses presented are of all enrolling centers and all Registry patients.
| Results |
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Registry Demographics and Representativeness of
Trial Patients
The 4595 registrants averaged 64 years of age, and 77% were male.
The mean left ventricular ejection fraction was 35%, and
77% had evidence of coronary artery disease (CAD). Of the 3579
nonrandomized patients, 1509 were AVID trialeligible (trial-eligible
arrhythmia and no medical exclusions) and 2070 were
noneligible.
AVID TrialEligible Patients
Reasons for Nonrandomization
The reasons for not randomizing eligible patients are given in
Table 1
. In these qualifying patients,
patient or family refusal, followed by physician preference, were the
most frequent causes for nonrandomization.
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Clinical Characteristics
Among trial-eligible patients, only a few statistically
significant differences between those randomized and those not
randomized were found. Randomized patients were slightly older (65.1
versus 63.4 years); more frequently were male (79.4% versus 74.5%);
more frequently had CAD (81.5% versus 75.7%) or a past history of
myocardial infarction (67.0% versus 58.3%), congestive heart failure
(CHF) (46.8% versus 41.8%), syncope (13.1% versus 9.5%),
hypertension (55.8% versus 47.9%), or diabetes (24.3% versus
20.6%); and less frequently had no evident structural disease (2.9%
versus 5.2%). However, the magnitude of the differences was small
(<15% proportionate or <5% absolute differences) and unlikely to
have a significant impact on enrollment or treatment decisions.
Cardiac procedures before or after the index arrhythmia were similarly distributed by randomization status in eligible patients. Overall, 28% had previously undergone bypass surgery, and 9% had had a percutaneous coronary intervention without differences between groups. After the arrhythmic event, 7.4% underwent bypass surgery and 3.2% a percutaneous coronary intervention. Nonrandomized patients rarely underwent ablation procedures (2%).
Discharge Cardiac Therapies
Discharge cardiac (nonarrhythmic) therapies were similarly
distributed in eligible patients in both groups, with 27% of patients
prescribed ß-blockers, 14% calcium antagonists, 34%
nitrates, 50% diuretics, and 24% warfarin. Two exceptions
were small differences in ACE inhibitor use (68.5% versus
57.6%, randomized versus nonrandomized) and aspirin use (59.1% versus
54.0%).
In each group of eligible patients, ICD and antiarrhythmic drug
therapies were used with equal frequency at discharge, with each being
used in
50% of patients (Table 2
). By
study design, both combination therapy (4%) and neither therapy (1%)
were to be avoided in randomized patients, whereas nonrandomized
patients could receive both therapies (11%) or neither therapy
(11%).
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Registry Patients Followed Up by the 1996 NDIS
A total of 4219 patients qualified for and were entered into the
Registry by December 31, 1996, and were followed for vital status
through December 31, 1996 (via the NDIS). The following is based on
these 4219 patients.
Clinical Characteristics
Table 3
presents the main
clinical characteristics of the Registry patients (including trial
patients) grouped according to presenting arrhythmia. Mean
ages ranged from 61 to 66 years. The prevalence of CAD ranged from 73%
to 82%. The range of mean ejection fractions was 32% to 41%. There
was a 2-fold difference in history of CHF (22% to 44%), but a history
of diabetes was present in
20% of all groups.
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Table 4
shows the postevent index
arrhythmia procedures and discharge therapies in the patients
grouped by presenting arrhythmia. Coronary bypass
surgery was performed in 42% of the transient VF/VT group, 17% of the
VF group, and
10% in other groups. There were substantial
differences in rates of arrhythmia ablation procedures (1% to
16%) and use of ß-blockers (23% to 44%), digitalis (29% to 43%),
ACE inhibitors (40% to 60%), and diuretics (34%
to 51%). The rate of ICD implantation varied from 20% to 58%
and the use of antiarrhythmic drugs from 30% to 60%.
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Survival
A relatively high rate of mortality was noted for all 6
arrhythmia groupings, with 2-year survival rates ranging from
76% in patients presenting with syncopal VT to 84% in patients
with unexplained syncope and inducible VT (Figure 4
) (P=0.007 among
groups).
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Survival was similar across arrhythmia groups for patients
without severe ventricular dysfunction (2-year rates ranged
from 82% to 86%, P=NS) but was more variable for
patients with poor ejection fraction (<0.35), with 2-year rates
ranging from 68% to 83% (P=0.021) (Table 5
).
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| Discussion |
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The AVID Registry constitutes the largest published cohort of patients with life-threatening ventricular arrhythmias of which we are aware.26 It consists of patients who were eligible for the AVID main trial and were randomized, those not randomized but qualifying for AVID, and those not randomized and not qualifying. Reasons for and frequency of not randomizing patients were recorded; nonrandomization most often was due to patient or family refusal, followed by physician preference. Interestingly, patient/physician preference (or bias) for drug and device treatments was virtually identical. A strong preference for an ICD over antiarrhythmic drug therapy (or vice versa) was not observed in this Registry population, suggesting the presence of little overall therapeutic selection bias in participating AVID centers.
Generalizability
The issue of generalizability of AVID's efficacy results to
the universe of patients with VT/VF is of prime importance. The
knowledge that AVID results were generated from a large percentage of
eligible patients (41%) and that nonrandomized but eligible patients
were strikingly similar also suggests that results of the study may be
applied with more confidence to AVID trialeligible patients seen in
clinical practice. In contrast, many other studies have enrolled a
small percentage of patients or have failed to keep a Registry, so that
the patient pool's "denominator" is unknown and
uncharacterized.17 Furthermore, several other VT/VF types
previously thought to be low-risk were found to be at a risk similar to
that of the AVID trialeligible patients. The surprisingly high and
similar mortality rates across the arrhythmia subgroups are
being investigated extensively, including ongoing collection of
additional baseline and follow-up data. Preliminary
multivariate analyses did not explain the
similarity of the high rates on the basis of well-known baseline risk
predictors, such as ejection fraction (Table 5
) or the choice of
antiarrhythmic therapy. The factors influencing treatment selection in
these nonrandomized groups are unknown, but given the approximately
equal use of ICD and antiarrhythmic drug therapy, as in the AVID main
trial, this finding raises the possibility that the expense of an ICD
may be justified by a potentially large but as yet unproven treatment
benefit in additional groups of patients, especially when associated
with a low ejection fraction (<0.35).
The lower and similar mortality observed for patients with left
ventricular ejection fraction
0.35 raises the question,
at least from a cost-effectiveness perspective, of the suitability of
ICD implantation in patients with relatively preserved left
ventricular function.
Transient/Correctable Cause of VT/VF
The high mortality rate for patients with VT/VF thought to be
provoked by reversible factors deserves special comment: 42% of
patients had in-hospital revascularization, 2%
ablation, and 4% pacemakers; many others had adjustment in medical
therapy (eg, potassium replacement). However, fewer than half (47%)
were discharged on specific antiarrhythmic therapy. Their poor
subsequent outcome (29% mortality at 3 years) suggests that clinical
judgment regarding reversibility and recurrence risk is not
very accurate and that more aggressive and specific antiarrhythmic
therapy (including ICD) may be appropriate for many of these patients,
especially if they have a low ejection fraction (<0.35).
Registry Caveats and Recommendations
Although the Registry form collected a substantial amount of
information, several subsequently proposed analyses would have
required that some data items be modified. These included details with
regard to primary versus secondary health insurer admission; discharge
dates of the first hospitalization related to the index
arrhythmia, in addition to the admission and discharge dates
for the screening hospitalization; and finally, performance and
results of electrophysiological studies
(including drug testing).
Although our process for follow-up through the NDIS may appear cumbersome, we found that it worked well. Total mortality (and death certificate codes) but not cause-specific mortality (ie, sudden death versus other causes) is available. Finally, characteristics of patients at sites that enrolled high and low numbers of patients were similar.
In conclusion, the AVID Registry design formed an important part of the AVID study program and has provided important information about the natural history of VT/VF, current practice patterns across a broad base of institutions, and a firm basis for generalizing the AVID study results to the general population of patients with AVID-type ventricular arrhythmias.
| Appendix 1 |
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| Appendix 2 |
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| Acknowledgments |
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| Footnotes |
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Received July 29, 1998; revision received December 8, 1998; accepted December 29, 1998.
| References |
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