Wearable Cardiac Defibrillator Protects Patients from Sudden Cardiac Arrest

Internal Medicine World Report, Summer 2011, Volume 1, Issue 1

Wearable Cardiac Defibrillator Protects Patients from Sudden Cardiac Arrest

Device Protects Patients during Vulnerable Period After an MI

By Lexa W. Lee

Awearable cardiac defibrillator (WCD) can help prevent sudden cardiac arrest (SCA) in patients during the 90-day period following discharge from a myocardial infaction (MI), according to findings presented at the 2011 American College of Cardiology meeting.

Following an MI, patients are at a higher risk for SCA for a period of 30 to 90 days, compared to other patients with coronary artery disease (CAD). The elevated risk is associated with factors like reduced left ventricular ejection fraction (LVEF) and continuing risk of ischemia, according to Thomas Deering, MD, lead author and chief of the Arrhythmia Center at the Piedmont Heart Institute in Pittsburgh, Pennsylvania. Although implantable cardiac defibrillators (ICDs) are sometimes used in these patients, such devices have not been found to reduce patients’ rate of SCA. The wearable cardiac defibrillator (WCD) is a device designed to provide such patients short term protection from SCA until their condition stabilizes sufficiently to make a more definitive decision about the use of an ICD.

“The strategy of immediate ICD implantation fails to recognize the frequency of significant recovery of ventricular function in the first few months following MI,” said Dr. Deering. “The WCD is ideal for short-term use during evolving arrhythmic risk when the guidelines do not support the implantation of an ICD.”

The researchers established a prospective registry called Wearable Defibrillator Use after Myocardial Infarction (WAMI) to evaluate the effect of WCD use in post-MI patients. None of the subjects met the criteria for an ICD at the time of enrollment. Data were collected on 90-day survival, patient compliance, frequency of appropriate treatment, and effectiveness of the WCD in preventing SCA.

The researchers enrolled 43 patients in the study. The group had a mean age of 61 years, 72% were male, and mean LVEF was 28.84%. The LVEF of 81% of the group was ≤ 35%, indicating a risk of irregular heartbeat or systolic heart failure. Twenty-two patients experienced a probable ischemic sustained or non-sustained ventricular arrhythmia in association with the MI. Post-discharge from MI, one patient experienced a 43-second episode of sustained ventricular tachycardia (VT) at a rate of 220 beats per minute. The VT was successfully normalized by the WCD. No deaths were observed among the subjects. After 90 days, 51% of the group had an EF > 35%, which meant they no longer qualified for a primary prevention (PP) ICD implantation. Another 19% of the group underwent a PP ICD implantation. Thirteen patients (30%) were lost to follow-up. The average length of use was 58.3 days, and the average daily use was 19.8 hours. Length of use was highly correlated to average daily use (p < 0.001) and age (p < 0.005).

The researchers concluded that a substantial percentage of patients who suffer a myocardial infarction will experience a significant improvement in left ventricular function within the first 90 days. This will subsequently lower the risk for sudden cardiac arrest, so that implantation of a defibrillator may be unnecessary. During the 90-day period following discharge from MI, a WCD can help prevent SCA.

There is a high rate of compliance among patients using WCDs after they become accustomed to wearing them, although some individuals may have occupational constraints or psychological barriers to using them, according to Dr. Deering. “WCDs are a bridge therapy for people waiting to make a decision about implantation, they can also allow patients to undergo appropriate therapy, like to improve renal function, before implantation, and they protect against SCA post-MI,” said Deering.

Author Disclosures: Thomas Deering is a minor researcher for ZOLL, Medtronic, St. Jude Medical, Boston Scientific, and Sorin; he is also a consultant for Medtronic and CorMatrix. Study was supported by ZOLL, Piedmont Heart Institute, and Morris Memorial Hospital.