Evaluation of a new pacing algorithm to prevent rapid tracking of atrial tachyarrhythmias.

The new SMARTracking (SMT) algorithm was evaluated in seven patients with the Intermedics Relay DDDR pacemakers and a history of atrial tachyarrhythmias. The SMT algorithm uses the sensor calculated rate to define a physiological band whose upper limit is defined by the SMT rate. Pacemakers were programmed to DDDR with SMT (DDDRSM), DDDR with Conditional Ventricular Tracking Limit (DDDRC), DDDR with standard upper rate behavior, and VVIR, for a period of one month each. Patients underwent a CAEP exercise test and 24-hour ECG Holter monitoring in each mode. They also had ambulatory ECG monitoring during daily activities including rest, slow and fast walk, stairs ascent and descent. Three patients were in atrial fibrillation during the daily activities protocol. Their ventricular rates were paced and highly irregular, in both DDDRSM and DDDRC modes. The heart rate was lower in DDDRSM than DDDRC at rest and low levels of exercise but not during more strenuous activity. Two patients in DDDRSM and 3 in DDDRC requested early change of their mode due to unacceptable symptoms. Two patients exhibited Wenckebach behavior at atrial rates below the upper rate limit in both DDDRSM and DDDRC modes. In conclusion, CVTL or SMARTracking are not adequate protection against atrial tachyarrythmias in patients with DDDR pacemakers.