Visualization of Regional Left Ventricular Mechanical Delay by Tissue Synchronization Imaging in Heart Failure Patients With Wide and Narrow QRS Complexes Undergoing Cardiac Resynchronization Therapy
Assessment of left ventricular mechanical asynchrony by noninvasive imaging is emerging as a leader in identifying responders (or nonresponders) of cardiac resynchronization therapy (CRT),1–3 and possibly in selecting patients with narrow QRS complexes for CRT.4 The figures illustrate the potential clinical utility of tissue synchronization imaging (TSI) for these 2 purposes. TSI is derived from tissue Doppler imaging, which portrays regional asynchrony on 2D echocardiographic pictures by transforming the timing of regional peak velocity during the ejection phase into color codes and overlying the moving myocardium. This allows immediate visual identification of a regional delay in systole while a quick quantitative measurement of regional delay can be taken. In a patient with heart failure with a wide QRS complex who had a favorable response to CRT, there was left ventricular reverse remodeling, the asynchrony index decreased from 52.1 to 34.2 ms after 3 months, and TSI showed the abolishment of lateral wall delay (from orange to green color coding; Figure 1A, B). In another patient with a wide QRS complex who was a nonresponder, there was no improvement in left ventricular volume. Despite left bundle-branch block, there was an absence of mechanical asynchrony on TSI, and, in fact, mechanical asynchrony was induced after CRT (Figures 2A, B). The asynchrony index increased from 18.7 to 28.0 ms after 3 months. A third patient with heart failure and a narrow QRS complex (90 ms) received CRT because of the presence of mechanical asynchrony. This patient had significant reverse remodeling, gain in ejection fraction, and the asynchrony index decreased from 39.2 to 25.9 ms. TSI showed the presence of moderate basal to mid-septal wall delay and severe lateral wall delay (orange to red color coding) as baseline, which was abolished after CRT (Figures 3A, B). The asynchrony index was calculated by TSI or tissue Doppler imaging as the standard deviation of time to peak systolic velocity during the ejection phase in a 6-basal, 6-mid-segmental model of the left ventricle. A cutoff value of >31.4 ms has been shown recently to predict a favorable response after CRT.3
Movies I, II, and III (corresponding to Figures 1, 2, and 3) are available in the online-only Data Supplement at http://circ.ahajournals.org/cgi/content/full/112/7/e93/DC1.
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