Cardiac resynchronization therapy (CRT) for treatment of resistant dilated cardiomyopathy (DCM) with disconjugate cardiac contractility (DCC) defined indirectly by ECG (QRS>130ms) is beneficial in 68% but ineffective in 32% of patients (Abraham et al, Bax et al). Directly demonstrating DCC before CRT treatment (defined currently by echo (Sogaard et al)) might improve outcome. MR is superior to echo in observing DCC and offers several means for its accurate quantitation. We examined the role of asymmetry (Ism) in terms of regional thickening and the role of asynchrony (Isn) in DCC with the principal aim of generating a robust numerical index for use in future trials of CRT.
METHOD AND MATERIALS
Measures of asymmetry and asynchrony in left ventricular heart contraction were developed in 12 normal subjects (6males, 6 females, mean age 51.4 + 14.0, range 23-76 years). Isn was determined from the spread of phases over which individual segments of the left ventricle achieved their maxima, averaged over two short axis slices. The methods were evaluated in ten DCM patients (EF<35 %), five CRT candidates (EF<35%, QRS>120ms), and seven normal subjects, using t-test and standardized differences (SD=sd/diff, Power (N) = number of patients to reach P<0.05) to determine efficacy (Altman, DG).
Measurements of asymmetry (Ism) and asynchrony (Isn) in left ventricular myocardial contraction distinguished control subjects from DCM patients with statistical difference (P<0.0001). There were three-fold differences between controls and DCM patients in Ism% and Ism could be measured with accuracy and provides excellent statistical power as markers. Isn in DCM patients and CRT candidates exceeded control in all cases.
1. Analysis of CVMR by MASS permits quantification of DCC for the individual patient. 2. Results indicate that DCC, measured by CVMR, increases 30 fold in DCM patients and in CRT candidates. 3. If asynchrony in heart contraction is the critical component of DCM to be corrected by CRT, CVMR is likely to be more cost effective in screening patients for this valuable but costly therapy.