Usefulness of tissue Doppler imaging for demonstrating altered septal contraction sequence during dual-chamber pacing in obstructive hypertrophic cardiomyopathy.

Dual-chamber pacing reduces left ventricular (LV) outflow obstruction in patients with obstructive hypertrophic cardiomyopathy (HC), the mechanism of which lies in pacing-induced paradoxic septal motion. This study was conducted to test the hypothesis that tissue Doppler imaging (TDI) could demonstrate changes in the septal contraction sequence during dual-chamber pacing in patients with HC. TDI was performed in 16 patients (5 women; mean age 63+/-11 years) who underwent dual-chamber pacing for 7.6+/-2.1 year. With and without pacing, the time to peak systolic myocardial velocity was measured from the basal, mid, and distal segments in the 4 different LV walls. Without pacing, there was almost no longitudinal segmental asynchrony. During pacing, however, marked longitudinal segmental asynchrony appeared, especially in the anteroseptal wall (from p=NS to p<0.01 by analysis of variance) and the ventricular septum (from p<0.05 to p<0.01), with the time to peak velocity extremely prolonged at the distal segments. This was associated with a modest but significant decrease in the LV pressure gradient (from 20+/-8 to 14+/-7 mm Hg, p<0.01). In patients with obstructive HC, altered septal contraction sequence accounts for the reduced LV outflow obstruction during dual-chamber pacing, which was clearly demonstrated by TDI.