IS ATRIAL SENSING OF VENTRICULAR FAR-FIELD SIGNALS IMPORTANT IN SINGLE-LEAD VDD PACING

In single-lead VDD pacing the atrial sensitivity frequently is program med to sensitive values. Atrial sensing of ventricular far-field signa ls should be reduced by differential atrial sensing. The aim of the st udy was to evaluate the effectiveness of this approach. Methods: The s tudy included 10 patients with a single-lead VDD pacemaker (Thera 8948 , Lead 5032). The atrial sensitivity was set to its most sensitive val ue of 0.18 mV and the telemetered intraatrial EGM was continuously rec orded. After atrial tracked ventricular pacing, WI pacing was performe d with pacing rates from 100 to 160 beats/min in steps of 10 beats/min and up to 165 beats/min. The peak-to-peak amplitudes of P waves (P) a nd ventricular far-field signals (VFFS) were measured from the recordi ngs. The ratio P/VFFS that defines the atrial signal-to-noise ratio wa s calculated and the time from stimulus to maximum of the far-field si gnals amplitude (Tmax) was measured. Results: P measured 0.98 +/- 0.76 mV. A VFFS was visible in the atrial channel in all patients with an amplitude of 0.45 +/- 0.25 mV (range 0.01-2.0 mV), independent of the pacing rate. The ratio P/VFFS was 3.9 +/- 4.2 (range 0.9-21.0). Tmax m easured 99.4 +/- 15.2 ms during sinus rhythm. A rate dependent shorten ing of Tmax to 92.7 +/- 11.2 ms at 140 beats/min was observed (P = 0.0 01). At rates above 140 beats/min no further shortening occurred. Conc lusion: Ventricular far-field signals are measurable in the atrial cha nnel of VDD systems and may reach considerable amplitudes, which are n ot rate dependent. Although differential sensing provides favorable P waves to ventricular far-field signal ratios, refractory periods are n eeded to avoid far-field sensing. The rate dependent shortening of the ventricular signal can be detected in the atrial channel in VDD pacin g.