The dependence of T wave alternans on diastolic resting period duration

The dependence of T-wave alternans on diastolic resting period duration as well as on regional differences in monophasic action potential duration was studied in the in situ dog heart. T-wave alternans was elicited when diastolic resting period shortened to values less than 41 +/- 6% of the cardiac cycle. This could be attained either by increasing the driving rate, or lengthening action potential duration by inducing hypocalcemia. During T-wave alternans, monophasic action potentials recorded from anterior and posterior left ventricular surface showed an alternation in duration; the degree in alternation in both regions differed and related to T-wave polarity.