Efficacy and safety of bipolar sensing with high atrial sensitivity in dual chamber pacemakers

In dual chamber pacemakers, atrial sensing performance is decisive for main tenance of AV synchrony. Particularly, the efficacy of mode switching algor ithms during intermittent atrial tachyarrhythmias depends on the sensitive detection of low potential amplitudes. Therefore, a high atrial sensitivity of 0.18 mV, commonly used in single lead VDD pacemakers, was investigated for its efficacy and safety in DDD pacing. Thirty patients received dual ch amber pacemakers and bipolar atrial screw-in leads for sinus node syndrome or AV block; 15 patients suffered from intermittent atrial fibrillation. Pa ce makers were programmed to an atrial sensitivity of 0.18 mV. Two weeks, 3 , 9, and 15 months after implantation, P wave sensing threshold and T wave oversensing thresholds for the native and paced T wave were determined. The myopotential oversensing thresholds were evaluated by isometric contractio n of the pectoral muscles. Automatic mode switch to DDIR pacing was activat ed when the mean atrial rate exceeded 180 beats/min. The patients were foll owed by 24-hour Holter monitoring. Two weeks after implantation, mean atria l sensing threshold was 1.81 +/- 0.85 mV(range 0.25-2.8 mV) without signifi cant differences during further follow-up. Native T wave sensing threshold was < 0.18 mV in all patients, in 13% of patients, paced T waves were perce ived in the atrial channel at the highest sensitivity. This T wave sensing could easily be avoided by programming a postventricular atrial refractory period exceeding 300 ms. Myopotential oversensing could not be provoked and Holter records showed no signs of sensing dysfunction. During a 15-month f ollow-up, 1,191 mode switch events were counted by autodiagnostic pacemaker function. Forty-two of these events occurred during Holter monitoring. Unj ustified mode switch was not observed. In DDD pacemakers, bipolar atrial se nsing with a very high sensitivity is efficient and safe. Using these sensi tivity settings, activation of the mode switch algorithm almost completely avoids fast transmission of atrial rate to the ventricle during atrial fibr illation.