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Measurements were made in 12 normal subjects and during induction ofsustained ventricular tachyarrhythmias in 31 patients with remote myocardialinfarction. QT interval measurements were made semiautomatically withcomputer assistance and the total QT interval was divided into early (QT 1 )and late (QT 2 ) components. QT intervals and QT interval dispersion betweentwo right ventricular endocardial sites were plotted against the degree ofprematurity of the last extrastimulus (S 2 , S 3 , or S 4 ). In the controlgroup, total QT and QT 1 intervals shortened with increasing prematurity ofthe last extrastimulus (p , 0.001). Slopes (positive) were steeper withfaster pacing rates (600, 500, or 400 ms) and more extrastimuli (1 to 3).The relationship between QT 2 intervals and prematurity of the lastextrastimulus was flat, but the slope was slightly negative (p=0.05to,0.001) and did not vary with changes in pacing cycle length or number ofextrastimuli. QT interval dispersion in the control group was minor(95% CI 0-40 ms). During induction of sustained ventriculartachyarrhythmias, total QT and QT 1 intervals were longer (y intercepts)than in the control group (p , 0.05 at 400-ms pacing cycle length) and theirdispersion was increased (p , 0.05). Generally, QT 2 intervals were shorter(p , 0.05 at 600-ms pacing cycle length) during induction of ventriculararrhythmias in comparison with the control group but dispersion wasincreased (p , 0.05 at 400-ms pacing cycle length). QT intervals and QTinterval dispersion show an orderly and predictable relationship withprematurity of the last extrastimulus in normal subjects. These patternsdiffer during induction of sustained ventricular tachyarrhythmias. Suchdifferences may be exploited to derive clinically predictive and usefulmeasurements. |
