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

Abstract

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 (IVCT). These delays may render the left heart AV intervals (LAV) either too short or too long, 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 preejection period (PEP) caused by RV pacing, as compared to normal depolarization pathway. Intrinsic IACT 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 + Ventricular Sense: LAV = RAV - IACT; Atrial Sense + Ventricular Pace: LAV = RAV + IVCT; Sequential AV Pace: LAV = RAV - IACT + IVCT.(ABSTRACT TRUNCATED AT 250 WORDS)

Automatic Beat‐to‐Beat Left Heart AV Normalization:

“…Symptoms cleared and exercise tolerance improved after a DDD pacemaker with a relatively short AV interval (100 ms) was implanted. This observation and several other publications 3,4 , 20–22 led to the conclusion that the left heart AV is the key determinant of cardiac performance, even at the expense of not entirely “normal” right heart AV or PR intervals.…”

“…Numerous publications attribute the nonphysiological nature of right heart DDD pacing to several pacing and sensing induced delays, thus increasing the acceptance of the left heart AV interval as an independent entity 3,4 , 12 , 25,26 . In heart failure patients, in whom the proper AV sequence may be critical, it was shown that there was clinical improvement when patients with LBBB and first‐degree AV block were paced with short AV interval 27–30 .…”

“…In addition, upgrading to DDD pacing resolved the problem of pacemaker syndrome in many patients with VVI pacemakers by carefully programming the AV interval 1,2 . However, evidence is now available about the adverse effects of right heart pacing on the left heart AV sequence 3–5 . Atrial sensing introduces a delay due to the time it takes the P voltage to reach the atrial sensing amplifier threshold.…”

Intra‐ and Interatrial Conduction Delay:

“…Right atrial pacing may reveal or enhance atrial conduction disorders depending on the site and rate of atrial pacing 35 , 116 (Fig. 6).…”

“…6). Several studies 116‐119 have shown the wide interindividual variability of intra‐ and interatrial conduction times in patients with pacemakers. In the series by Wish et al 118 the duration of interatrial conduction time in paced atrial cycles varied from 70 to 380 ms (mean 144 ± 82 ms).…”