Physical determinants of the endocardial P wave.
Reliable atrial sensing of intrinsic P wave activity is important to ensure optimal atrial or dual chamber pacemaker function. Various physical factors (e.g., posture, respiration, exercise) may influence P wave characteristics and impair adequate sensing. To investigate this phenomenon, we measured the average of three P wave amplitudes (PWA) and calculated slew rates from telemetered printouts acquired from Pacesetter pacemakers in 32 patients. These measurements were performed in various body positions, with upright exercise and in varying stages of respiration.


RESULTS
the mean supine PWA increased on full inspiration (3.56 +/- 1.3 mV versus 3.25 +/- 1.2 mV during quiet respiration, P less than 0.001), and also increased significantly with full expiration. The mean PWA increased on assuming the erect position (3.25 +/- 1.2 mV increasing to 3.49 +/- 1.3 mV, P less than 0.001); in the upright position, the mean erect PWA during quiet respiration was not significantly influenced by the stage of respiration. The mean upright exercise PWA did not differ significantly from the preexercise erect PWA (3.50 +/- 1.2 with exercise, and 3.47 +/- 1.5 before exercise; P = NS). Calculated slew rates were not different lying versus standing.


CONCLUSIONS
the mean supine PWA increases significantly at the extremes of respiration and on assuming the erect body position; upright exercise results in no appreciable change in the erect PWA. Atrial sensitivity adjustments based on standard supine testing should be adequate for all body positions.
Shandling
A H
AH
Memorial Heart Institute, Long Beach, California 90801-1428.
Florio
J
J
Castellanet
M J
MJ
Messenger
J C
JC
Crump
R
R
Evans
K
K
Rylaarsdam
A
A
Nolasco
M
M
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001824:Body Constitution; D004562:Electrocardiography; D004699:Endocardium / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006325:Heart Atria / Q000503:physiopathology; D006331:Heart Diseases / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial; D011187:Posture; D011446:Prospective Studies; D012119:Respiration