Presentation Title:

Microvolt Repolarization Alternans Identifies Response to Cardiac Resynchronization Therapy

Author Block:

Derek V. Exner, MD, MPH, Karen Cowan, RN, George Wyse, MD, PhD, Brent Mitchell, MD, Robert S. Sheldon, MD, PhD, Anne M. Gillis, Katherine M. Kavanagh, MD and Henry J. Duff, MD. University of Calgary, Calgary, AB, Canada

BACKGROUND. Cardiac resynchronization therapy (CRT) improves functional capacity in many patients with highly symptomatic heart failure, left ventricular dysfunction & conduction delay. However, there is significant variation in individual response to CRT. Given the cost & complexity of CRT, simple means to identify patients most likely to respond to CRT are required. The presence of microvolt beat-to-beat alterations in cardiac repolarization (T wave alternans; TWA) is related to cellular calcium flux. Since altered calcium handling is central in heart failure, we hypothesized that TWA assessment may aid in identifying patients likely to respond to CRT.
METHODS. Consecutive patients (n = 23) undergoing CRT had baseline TWA evaluation performed (RV pacing @ 109 bpm) via a commercial system (Cambridge Heart). Their mean age was 69 years, mean ejection fraction (EF) 0.21, mean QRS duration 172 msec & 74% had ischemic heart disease. All had NYHA class III (61%) or IV (39%) symptoms despite optimal medical therapy. Patients were followed for an average of 18 months post-CRT implantation.
Patients were categorized as clear responders if they improved ≥2 NYHA classes & had an absolute increase in EF ≥ 0.10. There were 12 (52%) clear responders. Baseline EF, QRS duration, & heart failure severity was similar in the 2 groups (p > 0.2). Patients who clearly responded had greater total TWA voltage (3519
μV) than patients who did not (1110 μV; p =0.001). TWA voltage was useful in identifying CRT responders (odds ratio 1.12, 95% CI 1.01 to 1.23; p=0.02; FIGURE). The positive & negative predictive values for identifying dramatic CRT responders were 73% & 67%, respectively.
CONCLUSION. TWA assessment may be useful in identifying patients more & less likely to respond to CRT. Additional studies evaluating the predictive utility of TWA assessment in identifying CRT responders are required.