Why an ICD is not useful soon after MI?

Why an ICD is not useful soon after MI?

Why an ICD is not useful soon after MI?: A substudy of the DINAMIT (Defibrillation in Acute Myocardial Infarction Trial) by Paul Dorian, Stefan H Hohnloser, Kevin E Thorpe, Robin S Roberts, Karl-Heinz Kuck, Michael Gent and Stuart J Connolly evaluated why an ICD is not useful soon after a myocardial infarction [1]. DINAMIT study had randomized those with recent myocardial infarction (6 to 40 days), left ventricular dysfunction (ejection fraction <35%) and a low heart rate variability to receive an implantable cardioverter defibrillator (ICD) or just standard medical therapy involving around six hundred and fifty patients (311 in the ICD group and 342 in the control group). It was a negative study in that ICD therapy failed to improve survival. The sub study concluded that ICDs do not reduce all cause mortality in those with a recent myocardial infarction because those who get an arrhythmic death averted by an ICD have a high ischemic burden and heart failure risk. This leads to higher mortality in the subsequent weeks or months. On the other hand, the lower risk group have less chance of ICD shocks as well as subsequent mortality. There was also a higher proportion of ventricular fibrillation (38%) rather than ventricular tachycardia, among the causes for appropriate ICD discharges, compared to other primary prevention trials. This may also be a marker of higher mortality risk. The study was not able to identify whether the arrhythmia needing the ICD shock caused deterioration of cardiac function or an additional factor caused both together. It could also not show whether the shock itself directly or indirectly lead to higher mortality. This was because the small number of deaths in subgroups limited the role of any such analysis. This study also highlights the fact that ICD therapy may not always mean averting a death. A competing risks analysis showed that those factors which increased the risk of arrhythmic death also increased the risk of non arrhythmic deaths. Reduction in sudden cardiac death by the implantable cardioverter defibrillator was fully offset by an increase in nonarrhythmic deaths, which were greatest in patients receiving defibrillator shocks.

The IRIS study also showed that prophylactic ICD therapy did not reduce overall mortality among patients with acute myocardial infarction and clinical high risk features [2]. The study enrolled 898 patients 5 to 31 days after myocardial infarction, if they had left ventricular ejection fraction 40% or less and heart rate 90 beats or more on first available ECG, and/or non sustained ventricular tachycardia at 150 beats per minute or more during Holter monitoring.

How to cover the arrhythmic risk in post myocardial infarction patients before they qualify for guideline recommended ICD therapy? An option is to bridge with a wearable defibrillator cardioverter (WCD) [3]. VEST Investigators randomly assigned 2302 patients with acute myocardial infarction and ejection fraction of 35% or less in a 2:1 ratio to receive WCD plus guideline directed therapy or to guideline directed therapy only. WCD did not significantly lower the primary outcome of arrhythmic death than control [4]. But a major problem regarding WCD is the compliance. Of the 48 participants in the device group who died, only 12 were wearing the device at the time of death.

References

1. Paul Dorian, Stefan H Hohnloser, Kevin E Thorpe, Robin S Roberts, Karl-Heinz Kuck, Michael Gent, Stuart J Connolly. Mechanisms Underlying the Lack of Effect of Implantable Cardioverter-Defibrillator Therapy on Mortality in High-Risk Patients With Recent Myocardial Infarction: Insights from the Defibrillation in Acute Myocardial Infarction Trial (DINAMIT). Circulation. 2010 Dec 21;122(25):2645-52.
2. Steinbeck G, Andresen D, Seidl K, Brachmann J, Hoffmann E, Wojciechowski D, Kornacewicz-Jach Z, Sredniawa B, Lupkovics G, Hofgärtner F, Lubinski A, Rosenqvist M, Habets A, Wegscheider K, Senges J; IRIS Investigators. Defibrillator implantation early after myocardial infarction. N Engl J Med. 2009 Oct 8;361(15):1427-36.
3. Francis J, Reek S. Wearable cardioverter defibrillator: a life vest till the life boat (ICD) arrives. Indian Heart J. 2014 Jan-Feb;66(1):68-72.
4. Olgin JE, Pletcher MJ, Vittinghoff E, Wranicz J, Malik R, Morin DP, Zweibel S, Buxton AE, Elayi CS, Chung EH, Rashba E, Borggrefe M, Hue TF, Maguire C, Lin F, Simon JA, Hulley S, Lee BK; VEST Investigators. Wearable Cardioverter-Defibrillator after Myocardial Infarction. N Engl J Med. 2018 Sep 27;379(13):1205-1215.