ABCD Trial Key Points

· MTWA (non-invasive, low-risk) is comparable to EPS (invasive) in predicting ventricular tachyarrhythmias and SCD.

· When MTWA and EPS are combined, predictive performance is improved even further.

Key Quotes:

“Recent randomized trials that selected patients for ICD insertion on the basis of reduced left ventricular ejection fraction (LVEF) alone (4,5) … demonstrated an improvement in mortality rates but did so with relatively low therapeutic efficiency (15 to 17 ICDs/life saved). Consequently, although guidelines recommend prophylactic ICDs in most patients with LVEF ≤ 0.35, the majority of inserted ICDs never deliver therapy (6). Concerns regarding device complications, including worsening heart failure, inappropriate shocks, and device recalls, and the impact on health care costs (7) have also prompted a re-examination of this strategy (8).”

“The ABCD trial provides a unique opportunity for comparing risk stratification strategies in a relevant and large cohort of patients. We found that ICD insertion directed by noninvasive MTWA testing is comparable to one guided by EPS in predicting the risk of ventricular tachyarrhythmias or SCD in patients with coronary artery disease, LVEF ≤ 0.40, and NSVT. In addition, by using the tests in a complementary fashion, the efficiency of SCD prevention is increased further.”

“Initial recommendations for ICD insertion for primary prevention of SCD included NSVT and inducibility at EPS (1,2). Such a strategy identifies a high-risk group of patients, but it is costly, invasive, and hence impractical for broad-based screening. Although EPS is no longer generally used for this purpose, excellent data show that the cost-effectiveness of primary prevention of SCD and reduction in total mortality are doubled if risk stratification is used to guide ICD insertion (9,19). Therefore, despite the evolution in practice standards, the results of the ABCD trial remain highly relevant to contemporary issues regarding optimal selection of patients for primary prevention of SCD. In fact, the comparable predictive accuracy of noninvasive MTWA testing carries significant clinical importance, because this test can obviously be applied more broadly in clinical practice than EPS.”

Additional notes:

· While the results of ABCD are fairly positive, the majority (87%) of all pts in ABCD had ICDs; thus, the endpoint issue likely impacted the results.  Hence, the NPV (95%) is slightly lower than previously reported studies.  Dr. Rosenbaum acknowledges the endpoint issue in the discussion.

“Because most patients (87%) received ICDs (i.e., a very sensitive detector of events) programmed in a consistent fashion, one can argue that by overestimating the number of SCD events, the ABCD trial underestimated the potential NPV that could be achieved by MTWA testing. This highlights an important limitation of surrogate end points derived from ICDs.”