Nonphysiological Left Heart AV Intervals as a Result of DDD and AAI "Physiological" Pacing

DDD and AAI pacemakers are considered physiological, since they preserve atrioventricular (AV) synchrony. Artificial pacing, however, is performed largely from right heart chambers, causing aberrant depolarization pathways. Pacing at the right atrial appendage (RAP) is known to delay left atrial contraction due to interatrial conduction time (IACT), and right ventricular (RV) apical pacing (RVP) delays left ventricular (LV) contraction due to interventricular conduction time (TVCT). These delays may render the left heart AV intervals (LAV) either too short or too Jong, thus affecting LV systolic function. The purpose of this study was to evaluate the actual LAV intervals during conventional, right heart AAI and DDD pacing. Resulting LAV intervals were compared to programmed AV values during all DDD pacing modalities. Ten patients with DDD and six patients with AAI pacemakers were studied. IACT was measured from the atrial spike to the onset of left P wave, as recorded by an esophageal lead. Systolic time intervals were measured using either a carotid pulse tracing or a densitogram (photoplethysmography). LV function was appraised by measuring rate-corrected LV ejection time (LVETc). IVCT was measured indirectly as the lengthening of LV preelection period (PEPJ caused by RV pacing, as compared to normal depolarization pathway. Intrinsic‘ACT and IVCT were considered zero. Right heart AV intervals (RAV) were measured from surface ECG and LAVs were calculated according to the following equations: Sinus Rhythm: LAV = RAV; Atrial Pace 4- Ventricular Sense: LAV= RAV ? IACT; Atrial Sense + Ventricular Pace: LAV = RAV + IVCT; Sequential AV Pace: LAV = RAV ? IACT + IVCT, Results: 1. IACT: mean = 73 msec, range: 35–130; IVCT: mean = 50 msec, range: 44–100. 2. Compared to RAVs, LAVs were either too short or too long (?130 to + 300 msec: P < 0.001 J in RAP 4- RVS and RAS + RVP. Conclusions: 1. LAV differed significantly from RAV during AP + VS and AS + VP. 2. “Physiological” RAV intervals in DDD and AAI may cause nonphysiological LAV, possibly affecting LV function. 3. IACT and IVCT should be accounted for when programming DDD PM to provide physiological LAV.