BACKGROUND Prevention of tachycardia is an important therapeutic strategy in patients with relaxation abnormality.

METHODS Eleven patients with stable relaxation abnormality (group 1) and 8 healthy individuals (group 2) were enrolled. Left ventricular (LV) mean diastolic pressure, LV dimensions, stroke volume (SV), and LV ejection, filling, and isovolumic times between right atrial pacing rates of 80 and 120/min were compared.

RESULTS Both groups 1 and 2 showed significant decreases in LV mean diastolic pressure when heart rate (HR) increased. At a HR of 80/min, no significant difference was noted between groups 1 and 2 in SV (51.4 +/- 13.0 vs 45.2 +/- 9.0 mL, P = .35). However, a decrement in SV between a HR of 80 and 120/min was significantly greater for group 1. Therefore, group 1 showed a significantly lower SV (30.2 +/- 7.1 vs 40.1 +/- 6.9 mL, P < .05) at a HR of 120/min. In terms of time intervals between HRs of 80 and 120/min, group 1 showed a significantly greater reduction in LV ejection time (84.5 +/- 20.1 vs 30.0 +/- 34.6 milliseconds, P < .005) and a smaller reduction in LV filling time (106.4 +/- 38.5 vs 166.3 +/- 30.7 milliseconds, P < .005) than group 2.

CONCLUSIONS Results of our study suggest that an inadequate SV response to tachycardia may play an important role in the production of dyspnea associated with tachycardia in these patients.