Aims: Single-pass VDD is a physiological stimulation mode which requires a single-lead with a floating dipole to detect the atrial signal. We investigated the impact of right heart dimensions on immediate and long-term atrial sensing stability in VDD systems to draw guidelines for optimal atrial sensitivity programming.
Methods: Forty-one patients (23 males, mean age 73 +/- 11 years) with II or III degree AV block and normal sinus node function received a Thera VDD Medtronic 8948 pulse generator with Medtronic 5032 lead. Atrial sensing was evaluated at pre-discharge and during 12-months follow-up in the supine and upright positions, during normal and forced breathing. Atrial sensing variability, quantified by a D value (mV), which represents the difference between the maximum and the minimum atrial electrogram amplitude obtained during the various activities, was analyzed and related to right heart dimensions measured at echocardiography.
Results: Long-term appropriate atrial sensing was obtained in 40/41 patients. P wave mean amplitude at pre-discharge, during every specific activity, was predictive of 12-month values. No atrial oversensing was observed. According to the right atrial dimension (RAD), patients with RAD > 38 mm had a sensing variability significantly higher than those with RAD < or = 34 mm (D=1 + 1 Vs D=0.4+/-0.5; P<0.05). A linear relationship between D and RAD dimensions was observed (r=0.47; P<0.005). According to the distance from the roof of the right atrium to the right ventricular apex (RAVD), patients with RAVD < 93 mm had D=1.1 +/- 1, while patients with RAVD > 93 mm had D=0.5 +/- 0.4; P<0.05); a inverse correlation between RAVD and D was highlighted (r=-0.43; P<0.01). Using a cluster analysis, the combination of RAD and RAVD identified a subgroup (RAD > 30 mm and RAVD < 80 mm) at high risk of loss of AV synchrony with 67% sensitivity and 80% specificity. Nevertheless, apart from heart dimensions, no patient showed an atrial signal amplitude lower than 0.3 mV.
Conclusions: According to our data, in VDD single-lead systems the amplitude of the atrial signal is stable over time in every physical activity. High RAD and low RAVD values may select patients with poor atrial sensing stability. Anyway, taking into account that no atrial oversensing was observed, atrial sensitivity setting at the highest value should be recommended.