To maximize the hemodynamic benefit of cardiac resynchronization therapy (CRT), echocardiographic AV interval optimization is routinely performed, complemented by VV interval optimization especially in non-responders. Programming of the basic pacing rate, however, is largely empirical in these patients. Therefore, the present study aimed to systematically evaluate the impact of basic pacing rate on hemodynamic parameters in CRT patients with sinus bradycardia.

We included 70 consecutive patients with moderate to severe heart failure, LV ejection fraction ≤35%, left bundle branch block or a QRS duration >120 ms combined with echocardiographic evidence of ventricular dyssynchrony. All patients were on optimal heart failure medication, with CRT-ICD devices implanted at least 6 months before inclusion into the study. All patients were in sinus rhythm with a spontaneous heart rate <40 bpm. In all patients, cardiac output (CO) and stroke volume (SV) were determined using electrical velocimetry (EV) (Aesculon, Osypka Medical, Berlin, Germany). EV provides a new algorithm to calculate CO based on variations in thoracic electrical bioimpedance, which has been recently validated. Hemodynamic measurements were performed at four different pacing rates ranging from 40 to 70 bpm. A stepwise increase in CO was encountered with increasing heart rates, reaching statistical significance when comparing 70 with 40 bpm. SV remained unchanged throughout all pacing rates.

In the range between 40 and 70 bpm, an increase in basic pacing rate enhances CO without reducing SV. According to this pilot study, a basic pacing rate between 60 and 70 bpm would appear reasonable.