Mode switching in dual chamber pacemakers

Aims Various mode-switching algorithms are available with different tachyarrhythmia detection criteria to be satisfied to initiate mode-switching. This study evaluated three different mode-switching algorithms in patients with paroxysmal atrial fibrillation. Methods and Results Seventeen patients completed the study. Three mode-switching algorithms were downloaded as software into the pacemaker, each for 1 month in a single-blind, randomized sequence. The criteria to initiate mode-switching were: mean atrial rate (‘standard’), ‘4-of-7’ or ‘1-of-1’ atrial intervals to exceed the atrial detection rate. Symptoms for each were measured using the Symptom Checklist–Frequency and Severity index. The median number of mode-switch episodes increased from 20 for ‘standard’ to 39 for ‘4-of-7’ (P=0·029 vs ‘standard’) and 103 for ‘1-of-1’ (P=0·0012 vs ‘standard’) onset criteria. Median duration of episodes decreased from 2·5 min with ‘standard’ to 1·4 min with ‘4-of-7’ and 0·4 min with ‘1-of-1’ onset criteria. Frequency of symptoms was lower using ‘4-of-7’ (18·2±12·0 vs 23±12·0, P=0·08) or ‘1-of-1’ (20·4±12·4 vs 23±12·0, P=0·07) than ‘standard’ onset criteria. Severity of arrhythmia tended to be less with either ‘4-of-7’ (16±10·4 vs 19·1±19·4, P=0·12) or ‘1-of-1’ (17·5±10·3 vs 19·1±9·4, P=0·18) than with ‘standard’ onset criteria. Conclusions The more sensitive onset criteria for detection of atrial tachyarrhythmias were associated with lower frequency and severity of symptoms.