P wave characteristics at rest and during exercise in normal subjects and patients with hemodynamic evidence of left atrial overload were compared. Three groups were studied, including 48 normal subjects, 15 patients with mitral stenosis, and 24 patients with left ventricular dysfunction. Frank lead electrocardiograms were recorded on magnetic tape at rest sitting and during upright bicycle exercise. Digital computer techniques were used to derive P wave area vectors. The initial 3/8 of the P wave were regarded as representing primarily right atrial, and the terminal 5/8 primarily left atrial activity. The P wave response to exercise in normal subjects include a small but significant (p<0.005) increase of the vertical component of the initial or right atrial vector and a significant (p<0.001) increase of the posterior terminal P vector component from 0.5 to 1.1 μV-sec. Analysis of area vectors in the abnormal groups at rest increased the recognition rate of left atrial overload over that obtained with standard 12-lead criteria, from 38 to 82% (P<0.005) at a specificity of 92%. The recognition rate during exercise was 67%, slightly lower than that at rest, due to increased inter-individual variation and exercise-induced changes in the normal group in the direction of the left atrial overload.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine