Abstract. Cardiac resynchronization therapy by means of biventricular pacing is a new treatment option for heart failure that has recently been approved. It has been shown that CRT improves long term survival. There is limited information on the CRT influence on ventricular arrhythmia appearance.

The aim of the study was to compare the occurrence of ventricular arrhythmia during right-ventricular pacing (RVP) and biventricular pacing (BiVP) in the short period after BiVP system implantation.

Methods. The study group consisted of 35 patients with permanently implanted BiVP system. 24 patients received DDD and 11 patients VVI pacing system. Patients with NYHA class from III – IV, EF < 35%, QRS > 150 ms were assigned to cardiac resynchronization therapy. In the period of 2 weeks after the implantation procedure the Holter monitoring during RVP and BiVP was performed. The pacing program (instead of resynchronization) and medication was unchanged and the time interval between the recordings was no more than 2 days. The number of ventricular extrasystoles (VES), pairs (VEP) and episodes of non sustained ventricular tachycardia (nsVT) were assessed. Patients didn’t significantly differ in the mean and maximal heart rate in the compared recordings. The Sign Test was used to compare data.

Results. During BiVP 60% of patients had lower number of VES, 70% lower number of VEP and 58% lower value of nsVT episodes in comparison to RVP. These differences were not statistically significant.

Conclusion. There is no difference in the arrhythmia occurrence, in the acute experiment, between biventricular and right ventricular pacing.