Atrial pacing and sensing characteristics in heart failure patients undergoing cardiac resynchronization therapy.

UNLABELLED Patients with heart failure and sinus rhythm undergoing cardiac resynchronization therapy (CRT) require the proper detection of atrial signals and reliable atrial pacing for AV-synchronous ventricular pacing. The study aim was to compare atrial pacing and sensing characteristics in patients with transvenous CRT and patients with standard pacing indications. METHODS The study group consisted of 31 heart failure patients with depressed left ventricular function and bundle branch block, and the control group of 124 patients with dual-chamber pacemakers because of standard pacing indications. The bipolar steroid-eluting atrial screw-in lead Tendril DX 1388 T (St. Jude Medical) was implanted and connected to pulse generators that provide similar diagnostic features. The unipolar pacing threshold at 0.4 ms duration, bipolar sensing threshold, and unipolar pacing impedance were determined at implantation and after 1, 3, and 6 months. RESULTS At implantation, the atrial pacing threshold was significantly higher in the CRT group than in the control group, 1.07+/-0.99 V versus 0.74+/-0.36 V (P<0.01). Similar pacing thresholds were recorded after 1 month. The pacing threshold in the CRT group was significantly higher at 1.46+/-0.92 V after 3 and 1.50+/-0.94 V after 6 months (control group: 0.96+/-0.25 V at month 3; 0.98+/-0.32 V at month 6; P<0.05). Sensing threshold was similar at implantation with 2.36+/-1.87 mV in the CRT and 2.54+/-0.78 mV in the control group. The sensing threshold in the CRT group decreased to 1.64+/-0.8 6mV after 3 and to 1.71+/-0.71 mV after 6 months and was significantly lower compared with the control group (2.16+/-0.57 mV at month 3; 2.27+/-0.9 8mV at month 6; P<0.05). At implant, the atrial pacing impedance was not different between the two groups with 443+/-156 ohms in the CRT and 416+/-116 ohms in the control group. During follow-up, the impedance became significantly lower in the CRT group compared with the control group (404+/-84 ohms versus 452+/-101 ohms at month 3; P<0.05). CONCLUSIONS Compared with patients with standard pacing indications, CRT recipients have less good electrical characteristics in the atrium. Atrial pacing and sensing function should be closely monitored in CRT patients.