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Real-Time 3D Echo in Patient Selection for Cardiac Resynchronization Therapy
Study Questions:
What is the utility of three-dimensional transthoracic echocardiography (3DE) for quantifying left ventricular (LV) mechanical dyssynchrony as a predictor of clinical and anatomical success of cardiac resynchronization therapy (CRT)?
Methods:
3DE was attempted in 187 patients at two institutions. 3DE was analyzed on a 16-segment model from which global LV ejection fraction (LVEF), diastolic and systolic volumes, and a systolic dyssynchrony index (SDI) were calculated. SDI was calculated as the standard deviation of the normalized time to minimal volume in each of 16 segments, expressed as a percent of cardiac cycle duration. A positive response to CRT was defined as an improvement by at least one New York Heart Association (NYHA) class, an increase in LVEF of 20%, or a 15% reduction in LV end-systolic volume (LVESV). A secondary endpoint was a >10% increase in LVEF.
Results:
3DE was not feasible in 22 patients (11.2%) and 19 patients were lost to follow-up, leaving 147 patients with baseline and follow-up echocardiograms. Average NYHA class was 3.0 ± 0.5, 78.9% were male, and average age was 66.4 years. An ischemic etiology for heart failure was seen in 70%, and 67% had classic left bundle branch block (LBBB). Average QRS duration was 136.7 ms and 83% had QRS duration ≥120 ms. Average baseline LVEF was 21.5% and baseline SDI was 14 ≥2%. An improvement in NYHA class was noted in 116 patients (78.9%), LVEF improvement ≥20% in 65%, and an LVEF increase ≥10% in 83.6%. LVESV decreased by 15% in 61 (41.6%) patients. For patients with ≥20% LVEF improvement, SDI declined by 5.9 ± 4.3% (p < 0.0001). Baseline QRS duration did not differ between patients with and without functional improvement. Baseline SDI was 15 ± 4.7 versus 10.1 ± 5.1% in those with and without functional improvement (p < 0.001). Receiver operator curve (ROC) analysis revealed an area under the curve of 0.52 and 0.79 for QRS duration and SDI, respectively. Similarly, baseline QRS duration was not predictive of LVEF increase, whereas SDI was significantly associated with LVEF increase in responders (16.2 ± 4.7%) and nonresponders (10.6 ± 4.4%) (p < 0.0001). ROC analysis revealed an area of 0.86, conferring a sensitivity of 91% and specificity of 71%. Reverse remodeling with a ≥15% reduction in LVSV occurred in only 41.6% of patients. SDI was predictive of this outcome, with a sensitivity of 92% and a specificity of 43%.
Conclusions:
LV dyssynchrony quantified by 3DE as an SDI predicts both clinical and anatomical responses to CRT.
Perspective:
Numerous echocardiographic techniques, typically using two-dimensional imaging, have been used in an effort to predict a response to CRT. While successful in smaller single-center studies, these data have suggested that these echocardiographic parameters are no more predictive than a reliance on electrocardiogram criteria alone. 3DE confers an advantage in a number of respects for assessing LV volume. By analyzing the entire contour of the LV, dyssynchrony in all regions is incorporated in an index of global mechanical dyssynchrony. Of note, these measurements were reproducible across two centers and also remained predictive for patients without typical classic indications such as those without classic left bundle branch block and patients with atrial fibrillation. While highly sensitive (90-92%) for predicting various favorable responses, specificity remained modest at 43-71%. These levels of accuracy would appear at least equivalent to and probably superior to previous echocardiographic methodology. It should be noted that the echocardiographic methodology used here did not utilize the latest generation of full-volume scanners. Whether utilization of the newer generation of full-volume scanners capable of real-time acquisition of the entire cardiac volume in a single heart beat would have provided improvement remains conjectural.
Keywords: Echocardiography, Three-Dimensional, Follow-Up Studies, Cardiac Volume, Heart Failure, Electrocardiography, New York, Systole, Cardiac Resynchronization Therapy
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