2. 1094 Circulation March 12, 2013
were the only ones who achieved significant CRT benefit
with QRS of 130 to 149 ms.18
Heart failure patients with left
bundle-branch block conduction obtained excellent benefit
from CRT, and there was no appreciable benefit from CRT
in patients with right bundle-branch block or intraventricular
conduction delay.19
It is quite clear that CRT does not achieve a favorable
result in patients with QRS durations <120 ms. On the other
hand, mechanical left ventricular dyssynchrony, an impor-
tant myocardial substrate for effective CRT, is exacerbated
by abnormal excitation of the left ventricle with a wide QRS
duration, especially when a left bundle branch conduction
disturbance is present. Although many factors influence the
cardiac responsiveness to CRT (lead position, type of cardio-
myopathy [ischemic versus nonischemic], extent and severity
of the myocardial damage, and sex), wide QRS complex and
left bundle-branch block are excellent electric biomarkers for
identification of heart failure patients who are likely to benefit
from resynchronization therapy.
Disclosures
Dr Moss reports a research grant from Boston Scientific to the
University of Rochester, of which he is a principal investigator.
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Key Words: Editorials ■ cardiac resynchronization therapy