Effects of Acute Volume Changes on P Wave Characteristics:

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Abstract
This study was performed to determine the effect on the P wave of different hemodynamic loads to the heart. Signal-averaged P wave ECG and atrial echocardiographic measurements were obtained from eight healthy male volunteers at rest and after infusion of 1000 mL of plasma expander (Haemaccel) over 15 minutes. These measurements were repeated 24 hours later at rest and after 0.8 mg of nitroglycerin given sublingually. The effect of positional changes was also studied. At rest the amplitude of the P wave and the time of the maximal the P wave amplitude were reproducible. Sitting increased heart rate variability; no significant changes of the P wave were found. Volume overload decreased the heart rate and increased the atrial size on echocardiography with changes in lead V1 (earlier appearance of the first positive deflection). Nitroglycerin administration increased heart rate and decreased the echocardiographic size of the atria, the latter not reaching statistical significance. Administration of nitroglycerin induced P wave amplitude rise in leads I and II. The maximal power in fast Fourier transformation for calculated orthogonal leads X and Y increased as well. Amplitude behavior in leads I, II, and V1 appears to correlate with load conditions, particularly with volume redistribution. In healthy men subtle changes in the P wave morphology after volume changes can be detected by the signal-averaged ECG. Application of these findings in patients following acute changes in circulation needs further investigation.