Limitations and Problems of Assessment of Mechanical Dyssynchrony in Determining Cardiac Resynchronization Therapy Indication - Is Assessment of Mechanical Dyssynchrony Necessary in Determining CRT Indication? (Con) -

Abstract

Patients with left ventricular (LV) systolic dysfunction and dilation frequently have ventricular contraction delay. Prolonged QRS duration is associated with abnormal activation. The conduction abnormality is associated with delayed depolarization and contraction of the lateral LV free wall. Sometimes a left bundle branch block has been developed in patients with severe heart failure. Contraction delay of the lateral LV free wall is increased by a left bundle branch block. Contraction delay of the lateral LV free wall can be improved by biventricular pacing. CRT is based on the principle of resynchronizing un-uniformed contraction of the ventricle. CRT improves the cardiac function, heart failure hospitalization, quality of life, exercise capacity and overall prognosis of patients suffering from heart failure. 1-7 In addition, CRT reverses LV remodeling. 8-12 The implantation of a CRT system is recommended for heart failure patients who remain in symptomatic New York Heart Association (NYHA) functional class III or IV despite optimal medical treatment with low LV ejection fraction ≤35% and a QRS duration ≥120 ms (130 ms in Japan). Prolongation of the QRS duration on an electrocardiogram (ECG) served as an indirect marker to identify mechanical dyssynchrony. However, approximately 30% of the patients who met the criteria do not respond to CRT. 2-6 The multicenter InSymc randomized clinical evaluation (MIRACLE) trial demonstrated that 35% of patients receiving CRT experienced no improvement in the heart failure clinical composite score. 4 No reverse remodeling is observed up to 40% in recent studies based on echocardiographic observation. 9 As ventricular pacing, even biventricular pacing, reduces contractility, existence of dyssynchrony is essential for CRT. One possible explanation for the lack of response for CRT could be the absence of sufficient dyssynchrony to allow the therapy to have any impact. Direct assessments of mechanical dyssynchrony might better select responder patients for CRT. Presence of scar tissue have also great impacts on the effect of CRT. Prolongation of the QRS duration on an electrocardiogram served as an indirect marker to identify mechanical dyssynchrony. One of the greatest problems is approximately 30% of the patients who met the criteria do not respond for CRT. One possible explanation for the lack of response for CRT could be the absence of sufficient dyssynchrony to allow the therapy to have any impact. Direct assessments of mechanical dyssynchrony might better select responder patients for CRT. However, RethinQ study demonstrated that patients with heart failure and narrow QRS intervals might not benefit from CRT, even with dyssynchrony. Moreover, the results of the PROSPECT study suggest given the modest sensitivity and specificity in the multicenter setting, despite training and central analysis, no single echocardiographic measurement of dyssynchrony could be recommended to improve patient selection for CRT beyond current guidelines. At present, assessment of mechanical dyss...

Right ventricular mechanics in hypertrophic cardiomyopathy using feature tracking

“…RV and LV electromechanical delay was measured as the difference between TTP (d-TTP) in 6 RV and 12 LV segments respectively (difference between the longest and shortest times 19,20 ). …”

Characterization of Left Atrial Mechanics in Hypertrophic Cardiomyopathy and Essential Hypertension Using Vector Velocity Imaging

“…11 Intra-A and inta-V dyssynchrony was defined as the standard deviation (SD) of the averaged time-to-peakstrain (TTP-SD). The LA and LV electromechanical delay was measured as the difference between TTP (d-TTP) in 12 LA and 12 LV segments, respectively, (difference between the longest and shortest cycle).…”

Myocardial Stretch in Early Systole is a Key Determinant of the Synchrony of Left Ventricular Mechanical Activity in vivo

“…10 Equally disappointing results were seen in other recent, large trials also. 11, 28 Although the mechanisms responsible for the apparent 'failure' of the echocardiographic measures of dyssynchrony continue to be debated, it is noteworthy that all the echocardiographic measures of mechanical dyssynchrony so far have concentrated only on the mid-to late-systolic, ejection phase of the cardiac cycle, with only little or no importance attached to the early systolic events. However, recent in-vitro experi-Early Myocardial Stretch and LV Synchrony…”