Paradoxical Behavior Of The Qt Interval During Exercise And Recovery And Its Relationship With Cardiac Memory

Background: Few studies have dealt with the behavior of the corrected (QT(c)) and uncorrected QT intervals during exercise and recovery.Hypothesis: Based on previously published dynamics of the QT interval during treadmill testing, this study attempt ed to reevaluate the computer-proposed underlying mechanisms of these dynamics and to determine whether the so-called memory phenomenon could be operative in some subjects without evidence of structural heart disease.Methods: This study included 42 unmedicated healthcare volunteers, 23 men and 19 women aged between 20 and 42 (mean 31.7) years. All had normal physical examinations, x-rays, and transthoracic echocardiograms. The electrocardiograms were also normal with 12-lead QT interval dispersions of < 90 ms.Results: During exercise and recovery, the behavior of the QT intervals permitted the categorization into two groups. In Group 1 (31/42; 73.8% of subjects) the uncorrected QT interval showed a biphasic pattern consisting of a gradual decrease during incremental exercise followed by a gradual increase during recovery In contrast, the QT(c), interval had a triphasic pattern resulting from a slight increase during the early phase of exercise, a gradual decrease at the highest rates, and a final increase during recovery as the rate slowed to control values. In Group 2 (11/42; 36.2% of subjects) the behavior was considered as paradoxical since the uncorrected QT interval displayed in a triphasic pattern whereas the QT(c) interval yielded a tetraphasic pattern due to the fact that both showed a second decrease during recovery while the rate was decreasing.Conclusions: Analysis of dynamics behavior of the QT(c) and the uncorrected QT intervals during exercise showed that some normal subjects had a paradoxical behavior which, because of its temporal relation to the phases of exercise, could be an expression of the so-called memory phenomenon.