In patients with acute myocardial infarction (MI) and a left ventricular ejection fraction (LVEF) equal or less than 35%, the use of wearable cardioverter defibrillator early after the MI did not lead to significant lowering of death from arrhythmia or from any cause, according to a new study published in the New England Journal of Medicine.
ICD is necessary .. but when?
The current guidelines recommend the implantation of an Implantable Cardioverter Defibrillator (ICD) in patients with MI and a LVEF of 35% or less. However, implantation is recommended after 40 days of the MI (or 90 days if revascularization was done). The evidence shows no benefit of early ICD implantation but the high mortality from arrhythmia in this period necessitates further research.
“We would advocate for a thorough discussion with the patient that both acknowledges the limitations of the available evidence and provides an understanding of the potential harms, such as frequent device alarms and potential for inappropriate shocks. In the context of a particularly motivated patient who is at high risk, we would still offer the wearable cardioverter–defibrillator.” – Dr. Michael Field, MD
Dr. Michael E. Field (Medical University of South Carolina and Ralph H. Johnson Veterans Affairs Medical Center, Charleston) and Dr. Richard L. Page (University of Wisconsin School of Medicine and Public Health, Madison) said in the accompanying editorial, “This paradox of increased risk of sudden cardiac death but lack of benefit with an ICD early after myocardial infarction has prompted interest in identifying a noninvasive intervention that could benefit this population of patients.”
In this randomized, multicenter, controlled trial, a total of 2302 patients were assigned in a 2:1 ratio to receive either the wearable cardioverter defibrillator plus the guideline-directed therapy (the device group) or the guideline-directed therapy alone (the control group) respectively. The primary outcome was the composite of sudden death or death from ventricular arrhythmia at 90 days while the secondary outcome was death from any cause or nonarrhythmic death.
The primary outcome occurred in 1.6% of patients in the device group and 2.4% of patients in the control group (RR 0.67; 95% CI 0.37-1.21; P=0.18). Death from any cause occurred in 3.1% and 4.9% of the patients in the device and control groups respectively.(RR 0.64; 95% CI 0.43-0.98; uncorrected P=0.04). Nonarrhythmic death occurred in 1.4% and 2.2% of the patients of the device and control groups respectively.(Relative Risk 0.63; 95% CI 0.33 to 1.19; uncorrected P=0.15).
Why was the study underpowered?
The authors estimated a 58% lower rate of the primary outcome in the device group for the study to be powered, however, this rate was not met. The difficulty of identifying all the cases that died due to arrhythmia may have contributed to the study being underpowered. “It is difficult to determine an arrhythmic cause of death accurately for unwitnessed deaths or deaths with limited documentation.”, the authors commented. Nonadherence to wearing the device (especially after two weeks of the MI) may also have reduced the power of the study.
Dr. Field and Dr. Page added, “The wear time with the device was lower than anticipated. Over the course of the trial, the percentage of patients who wore the wearable cardioverter–defibrillator on a given day fell from 81% just after randomization to 41% at 90 days, which was lower than had been estimated for the trial power calculation.”
When asked whether a wearable cardioverter defibrillator should be provided to patients with MI while they are waiting for ICD implantation, Dr. Field and Dr. Page answered, “We would advocate for a thorough discussion with the patient that both acknowledges the limitations of the available evidence and provides an understanding of the potential harms, such as frequent device alarms and potential for inappropriate shocks. In the context of a particularly motivated patient who is at high risk, we would still offer the wearable cardioverter–defibrillator.”
From social media
Would you want to wear a LifeVest if you had a large MI with an ejection fraction under 35%? Discuss
— C. Michael Gibson MD (@CMichaelGibson) September 29, 2018
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