Heart rate turbulence after atrial and ventricular premature beats: relation to left ventricular function and coupling intervals.

UNLABELLED: Heart rate turbulence (HRT) represents a biphasic chronotropic response of the sinus node to a single ventricular premature beat (VPB).
OBJECTIVES: To determine whether HRT is present after an atrial premature beat (APB) and to investigate the effects of paced VPB and APB coupling intervals on HRT quantifiers in patients with and without left ventricular dysfunction.
METHODS: A total of 37 subjects (54 +/- 16 years, 32 men) referred for electrophysiologic evaluation for ventricular tachycardia underwent a stimulation protocol consisting of 3 series of single atrial and ventricular extrastimuli with coupling intervals decremented from 750 to 400 ms at a 50 ms-step. Turbulence onset (TO) and turbulence slope (TS) after an APB and a VPB were calculated separately using a dedicated computer algorithm.
RESULTS: After an APB, TS was significantly attenuated (3.95 +/- 0.99 vs 8.32 +/- 1.9 ms/RR, P < 0.008) and TO was positive (1.37 +/- 0.35% vs -2.03 +/- 0.42%, P < 0.001) compared with those after a VPB. There was a strong correlation between TS (r = 0.71, P = 0.0002) but not between TO (r = 0.07, P = 0.074) after an APB and a VPB. In subjects with normal ejection fraction, the prematurity of ventricular coupling intervals was strongly related to TO (r = 0.68) and TS (r = -0.61), P < 0.0001 for both. These effects were less pronounced in patients with left ventricular dysfunction (TO: r = 0.25, P < 0.01; TS: r = -0.07, P = ns). No correlation was found between the APB coupling interval and TS or TO in both groups.
CONCLUSIONS: An APB induces HRT but the response is substantially attenuated and is not influenced by the APB coupling interval. In contrast to a VPB, TO is positive after an APB. Lack of correlation between HRT after a VPB and the VBP coupling interval indicates blunted baroreflex response in patients with left ventricular dysfunction.