ABSTRACT & COMMENTARY
Prognosis of Ventricular Fibrillation in Acute Myocardial Infarction
By Michael H. Crawford, MD
Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco
This article originally appeared in the March 2014 issue of Clinical Cardiology Alert. It was peer reviewed by Ethan Weiss, MD, Assistant Professor of Medicine, Division of Cardiology and CVRI, University of California, San Francisco. Dr. Crawford reports no financial relationships relevant to this field of study, and Dr. Weiss is a scientific advisory board member for Bionovo.
Source: Bougouin W, et al. Incidence of sudden cardiac death after ventricular fibrillation complicating acute myocardial infarction: A 5-year cause-of-death analysis of the FAST-MI 2005 registry. Eur Heart J 2014;35:116-122.
At this time, ventricular fibrillation (VF) early after acute myocardial infarction (MI) is not an indication alone for an implantable cardioverter-defibrillator (ICD) therapy. However, there is concern that despite the efficacy of mechanical and pharmacological therapy for acute MI, the risk of subsequent sudden cardiac death (SCD) in patients with VF complicating acute MI may be higher and the guidelines should be revisited. Thus, these investigators from the French registry on Acute ST-elevation and non-ST elevation Myocardial Infarction (FAST-MI) registry enrolled 3670 patients with acute MI in October 2005 and reported the 5-year follow-up data from this study population. Enrolled patients had to present within 48 hours of symptom onset and meet the international definition of acute MI. Excluded were iatrogenic MIs (e.g., postsurgical). The primary endpoints were deaths, classified as sudden cardiac death (SCD), non-SCD, and non-cardiac deaths, and related to early (< 48 hours after admission) or late (prior to hospital discharge) VF. A variety of clinical and demographic features were used in a multivariate model.
The incidence of in-hospital VF was 3.2% with 79% being early. VF patients were younger and more often smokers compared to the rest of the MI population. Beta-blocker therapy did not differ according to VF occurrence. Only anterior MI location was associated with VF occurrence. Interestingly, the presence of atrial fibrillation on the first ECG was associated with VF by multivariate analysis (hazard ratio [HR], 2.5; 95% confidence interval [CI], 1.4-4.4; P = 0.003). In-hospital mortality was higher in the VF group (25% vs 5%; P < 0.001) with an adjusted HR of 7.38 (95% CI, 4.27-12.75; P < 0.001). Also, mortality was higher with early vs late VF (33% vs 23%; P < 0.001). In-hospital death in the VF group was mainly from arrhythmias (82%) whereas cardiogenic shock was the most common cause in non-VF patients (62%). The overall survival at 5 years was 74% and was not associated with the occurrence of in-hospital VF on multivariate analysis. Also, the incidence of SCD was not more frequent in the VF group (13% in both groups at 5 years) despite a very low rate of ICD placement (1.2% overall). The authors concluded that the development of VF in the acute phase of MI was associated with a higher in-hospital mortality, but not long-term mortality or SCD.
Commentary
It seems that the indications for ICD placement just keep expanding, so it is interesting to see results that go against this trend. The VF group in this study was different from the rest of the MI patients in that they had lower LVEFs and were more likely to be on ACE/ARB and amiodarone. Also, they were more likely to have an ICD (3.4% vs 0.2%, P < 0.001), but the overall ICD rate in this study was low (about 1%). Despite these differences, neither the raw or adjusted HRs reached significance for a worse prognosis in the VF patients who survived the initial MI and could be followed long-term. Prior studies employing ICDs early (< 40 days) after MI, so-called primary prevention, showed no benefit. Now this study, which could be viewed as an observational study of secondary prevention of SCD, has shown that even in patients with VF early post MI, no benefit is likely to be obtained from ICD placement. This result is in agreement with the current guidelines and prior smaller studies.
The results also support our practice of ECG monitoring of all patients after an acute MI, since those who developed VF had a higher in-hospital mortality. However, it leaves the duration of such monitoring unclear. This is an issue since the deployment of primary PCI has decreased hospital stays for acute MI patients who are treated promptly and successfully. Bucking this trend may be difficult in the current hospital cost-containment era, and perhaps we should be giving more thought to placing a defibrillator vest on higher-risk patients being discharged early. My current practice is to keep all acute MIs in the hospital on ECG telemetry monitoring for a minimum of 48 hours. Those deemed at higher risk, such as patients with LVEF < 35% who may meet ICD criteria later (> 40 days), I am sending out with a defibrillator vest. However, this is a fast-moving field and further guidelines are sure to be emerging.
This study has limitations. It is an observational registry study, but the numbers of subjects are large, permitting robust statistical adjustments. It is a multicenter study and no control was exercised on the protocols used at each hospital. Also, categorizing cause of death can be challenging, but standard definitions were used and carefully adjudicated. Thus, for this type of study, it was well conducted.
