Feasibility and sensing thresholds of temporary single-lead VDD pacing in intensive care

Long-term pacemaker treatment of patients with a high-degree atrioventricular (AV) block routinely uses AV synchronous pacing because of its hemodynamic advantages compared with VVI pacing. In cases of temporary pacing, however, the limitations inherent in attempting to reliably position a temporary atrial lead generally influences the use of VVI pacing. We therefore tested the use of temporary single-lead VDD pacing, making AV pacing possible with only 1 lead, in 22 patients requiring temporary pacing due to a high-degree AV block. AV synchronous stimulation was achieved in all patients using a quadripolar lead with an atrial dipole with the atrial rings spaced 30 mm apart. During follow-up (14.1 +/- 12.5 hours) intermittent undersensing was detected in 4 of the 22 patients. We initially evaluated the atrial sensing threshold by decreasing the pacemaker device sensitivity stepwise in all patients (1.54 +/- 1.08 mV; n = 22). In 15 patients an intra-atrial electrocardiogram was recorded. During the breathing cycle, the maximum P-wave amplitude was significantly different from the minimum P-wave amplitude (2.19 +/- 1.00 mV vs 1.25 +/- 0.65 mV, p < 0.005). The atrial signal detected by the single lead was further analyzed in 10 of 15 patients using various filters. A mean signal loss of 45% was observed, increasing the lower bandpass frequency from 0.1 to 40 Hz (1.73 +/- 0.71 mV vs 0.92 +/- 0.51 mV, p < 0.02). Lowering the upper filter range from 1,000 Hz down to 100 Hz did not significantly influence the atrial signal (1.73 +/- 0.71 mV vs 1.61 +/- 0.75 mV, NS). Single-lead VDD pacing, even on a temporary basis, is a reliable means of achieving AV synchronous pacing. Due to the floating atrial dipole, the system is characterized by a high degree of variability in the atrial signal with intermittent lower values. A significant signal loss must be expected when a lower bandpass frequency of 40 Hz is used.