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Abstract & Commentary
Synopsis: The setting in which nonsustained VT is identified is an important diagnostic factor and is associated with a greater likelihood for inducing sustained ventricular tachycardia and lower overall survival.
Source: Pires LA, et al. J Am Coll Cardiol. 2001;38: 1156-1162.
The multicenter unsustained tachycardia trial (MUSTT) was a study designed to evaluate the predictive value of electrophysiologic (EP) studies and the efficacy of EP-guided therapy in post-MI patients with low ejection fractions and nonsustained ventricular tachycardia (VT). In this report, Pires and colleagues describe the influence of the clinical setting (in-hospital vs out-of-hospital) during which the index episode of nonsustained VT was recorded on the inducibility of VT, the rates of arrhythmic events, total mortality, and the effects of treatment. For the purpose of this paper, enrolled patients were classified as "in-hospital" if their nonsustained VT for entry into the trial had been recorded on hospital telemetry, and as "out-of-hospital" if it had been documented during an outpatient ambulatory electrocardiogram. Cumulative event rates were estimated using the Kaplan-Meier method. Estimated relative risks were expressed as hazard ratios based on the Cox proportional hazards model.
A total of 2202 patients were enrolled in MUSTT, and data regarding the clinical setting in which the index nonsustained VT was documented were available for 2190 of these patients. Of this latter group, 1631 (74.5%) were classified as "in-hospital" patients and 559 (25.5%) were classified as "out-of-hospital" patients.
There were many differences between the out-of-hospital and the in-hospital groups. The in-hospital group was slightly older and included a higher proportion of non-Caucasians. The mean cycle length of nonsustained VT was slightly shorter (410 vs 440 msec), and of longer mean duration (5 beats vs 4 beats) in the in-hospital group. In-hospital patients were more likely to have 2- and 3-vessel coronary disease, a myocardial infarction within either 1 month or 1 year, a history of congestive heart failure, and class III New York Heart Association Functional Class. Thirty-eight percent of the patients in the in-hospital group had an inducible VT vs. 32% of the patients in the out-of-hospital group. Event rates during follow-up were first analyzed among the untreated patients. The 2- and 5-year rates for cardiac arrest or arrhythmic death were 14% and 28% among in-hospital patients and 11% and 21% for out-of-hospital patients. Total mortality rates at 2- and 5-year follow-ups for the 2 groups were 24% and 48% for the in-hospital group and 18% and 38% for the out-of-hospital group. Rates for cardiac arrest or arrhythmic death and overall mortality were then adjusted for multiple risk factors. The adjusted hazard ratio was 1.24 for the in-hospital group vs. the out-of-hospital group for both arrhythmic events and total mortality.
Pires et al conclude that the setting in which nonsustained VT is identified is an important diagnostic factor. It is associated with a greater likelihood for inducing sustained VT and lower overall survival. Clinical factors that led to the initial hospitalization, however, explained much of these differences.
In 2 previous reports, the MUSTT investigators have described a benefit of implantable cardioverter defibrillator (ICD) therapy in patients after myocardial infarction with depressed left ventricular ejection fractions and nonsustained VT and slightly higher rates of arrhythmic events and death among untreated patients based on ability to induce VT.1,2 This follow-up analysis of the MUSTT database points out that the MUSTT study patients often had their nonsustained VT detected in-hospital during an admission for another cardiac or noncardiac condition. Patients who require hospitalization are usually at higher risk for future events than are stable out-patients. This study therefore supports other trials that have shown the greatest benefit of therapy in highest-risk patients. These include patients with advanced age, the lowest ejection fractions, and the most severe congestive heart failure. The data also argue against the value of periodic ambulatory ECG screening in out-patients who are otherwise doing well. These patients would have a lower probability of having an inducible VT and a lower event rate whether they had inducible VT.
1. Buxton A, et al. N Engl J Med. 1999;341:1882-1890.
2. Buxton A, et al. N Engl J Med. 2000;342:1937-1945.