On the clinical value of calibrated displacement apexcardiography.

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Abstract
A new type of displacement transducer for recording the calibrated left apexcardiogram (QLAC) has been evaluated in 69 normal subjects and 99 cardiac patients. Total displacement of QLAC (TD), its peak first derviative (peak dD/dt (t-peak dD/dt). A strong corretation exists between peak dD/dt and TD in normal subjects (r=0.95) and the deviation from the normal relationship allows a separation between normal and abnormal ventricular function. In normal subjects (dD/dt/Dt) max averaged 34.2 plus or minus 5.7 sec-1; it was signigicantly lower in patients with congestive cardiomyopathy (26.5 plus or minus 6.3 sec-1 p greater than 0.005). This index correlates with left ventricular end-diastolic pressure (LVEDP) (R = - 0.69) and with ejection fraction (R - 0.66) and behaves as expected during positive and NEGATIVE INOTROPIC interventions. The index (dD/dt/Dt) max is superior to TD and peak dD/dt, being less variable independent of thorax circumference and better correlated with hemodynamic parameters. The index t-peak dD/dt was 53.9 plus or minus 9.5 msec in normal subjects and 81.6 plus or minus 18.9 msec in patients with congestive cardiomyopathy (p greater than 0.001). This time-interval correlates weakly with LVEDP (R = 0.04) and with ejection fraction (R = - 0.66). It is concluded that the normalized first derivative of QLAC provides useful information on left ventricular function.