Positive EP Test Helps ID Post-MI Patients for ICDs

January 02, 2014

SYDNEY, AUSTRALIA — Post–MI patients with severe left ventricular dysfunction who have a negative electrophysiologic study (EPS) showing no inducible ventricular tachycardia (VT) can do without the protection of an implantable cardioverter defibrillator (ICD), a new study shows[1].

The patients in the series, all with a left ventricular ejection fraction (LVEF) <30% or LVEF <35% with heart failure, had low long-term rates of arrhythmia or death if VT could not be induced during electrophysiology testing, report investigators.

"We found that EPS-negative patients with severe LV dysfunction had a similarly good long-term prognosis as patients with preserved LVEF," write Dr Sarah Zaman (University of Sydney, Australia) and colleagues in their study, published December 31, 2013, in Circulation.

As the Australian researchers explain, the evidence supporting the use of ICDs as primary prevention in post-MI patients is derived from studies that use LVEF as the selection criteria, such as MADIT and SCD-HeFT . They point out that LVEF alone has a low specificity for arrhythmic vs nonarrhythmic deaths and that deaths frequently occur in patients above the LVEF cutoff.

Other studies have suggested that EPS, when used in conjunction with LVEF, could help identify a subset of post-MI patients who would derive the most benefit from ICD therapy.

In the present study, consecutive patients treated with PCI for ST-segment-elevation MI (STEMI) underwent early LVEF assessment. Of these, 128 patients with LVEF <30% or <35% with NYHA class 2 or 3 heart failure also underwent EP testing. ICDs were implanted in less than 0.1% of control patients (the 1286 post-MI patients with a LVEF >40%), 4% of those with a negative EPS (against study protocol), and 90% of patients with a positive study.

Regarding the primary end point, defined as survival free of resuscitated cardiac arrest or sustained VT/ventricular fibrillation (VF), the results were similar in the control group and in those with left ventricular dysfunction and an EPS-negative study. At three years, 91.8% of control patients and 93.4% of the EPS-negative patients were alive and without arrhythmia (resuscitated cardiac arrest/sustained VT/VF). Comparatively, just 62.7% of patients with left ventricular dysfunction and a positive EPS test were alive and without arrhythmia at three years.

"Our findings suggest that within the subgroup of post-MI patients with LVEF ≤35%, low-risk patients exist who would derive little benefit from an ICD," write Zaman and colleagues. "Restricting ICD implantation in this group through the additional use of EPS could allow a substantial cost benefit without a sacrifice in population life expectancy."

Interpret Results With Caution

In an editorial[2], Dr Alfred Buxton (Beth Israel Deaconess Medical Center, Boston, MA) said the results should be interpreted with caution, given the small study population and relatively few clinical events during the short follow-up period. In addition, the patient populations differ from MADIT and SCD-HeFT, in that these trials enrolled patients an average of three years after the initial MI. Other ICD trials, such as MUSTT and MADIT-II also included patients with symptomatic heart failure that could have contributed to the risk of sudden cardiac death (SCD) in a way that would not have been detected by a positive EPS.

"The results of this study suggest that judicious application of a [positive EPS] should be considered a standard part of the process we use to stratify patients for risk of SCD after MI," writes Buxton. "However, lessons from previous trials warn us that risk stratification cannot rely on single tests alone but require consideration of multiple risk factors."

He adds that until clinicians and the clinical guidelines move beyond the "current fad" of stratifying patients based on EF, "we will continue to waste money and harm patients, implanting ICDs in many that will not benefit and withholding them from patients whose survival could be improved with ICD treatment."

The researchers have disclosed no relevant financial relationships. Buxton has received research grant support from Medtronic and honoraria from Boston Scientific, Medtronic, and St Jude.

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