Measurement of Vmax of the cardiac action potential with a sample/hold peak detector.

A simple device for measuring the maximum upstroke velocity (Vmax) of the cardiac action potential is described. It consists of a differentiator, filter, and sample/hold peak detector. The sample/hold cycles are automatically set by the stimulus. The circuit can drive a standard pen recorder and digital voltmeter, resulting in rapid and accurate measurements. An example of the effect of quinidine on the upstroke of the cardiac action potential is shown. The circuit can easily be adapted to other applications.