Clinical study of “A waves” (atrial waves) in impedance cardiograms

Abstract

In impedance cardiograms taken by Kubicek's method,1 two preejection waves (the A wave and B wave) are seen. This study is concerned with various aspects of the A wave and the information it contains. From the fact that the A wave never occurs during atrial fibrillation but always appears following the P wave of the ECG in cases of sinus rhythm and first degree or complete atrioventricular block and that an impedance change occurs during the ventricular isometric contraction phase, it may be seen that the impedance change represented by the A wave arises from volume changes due to the active atrial contraction. The maximum value of the first derivative of the A wave (A dZ/dt max) was found not to correlate with the maximum left atrial volume, but to correlate to a small degree (r=0.47, p<0.05) with the mean pulmonary artery wedge pressure, and to a high degree (r=0.91, p<0.005) with the left atrial contraction rate. These facts lead to the conclusion that A dZ/dt max may be a noninvasive indicator of atrial contractility. Using this indicator, it was possible to investigate changes in atrial contractility arising from the Frank-Starling effect and from the increased contractility of the atrial muscles themselves in cases of complete AV block and sick sinus syndrome. Concerning the difference of A dZ/dt max found in different classes of patients, it was found that it is lowest in normal young adults and higher in IHD and MVD cases, in which the left atrial load has been increased. Finally, results were obtained which indicate that the high value of A dZ/dt max found in many cases of NCA is caused by increased atrial contractility due to autonomic imbalance.