Krahn Andrew D, Yee Raymond, Chauhan Vijay, Skanes Allan C, Wang Jian, Hegele Robert A, Klein George J
Division of Cardiology, University of Western Ontario, London, Ontario, Canada.
Am Heart J. 2002 Mar;143(3):528-34. doi: 10.1067/mhj.2002.120408.
This study was performed to evaluate the impact of beta blockers on QT adaptation to heart rate during the exercise and recovery phases of exercise testing in long QT syndrome.
Long QT syndrome is characterized by familial syncope and sudden death in the context of sudden heart rate changes. QT hysteresis has been proposed as a phenotypic marker of long QT syndrome, suggesting altered QT adaptation to changes in heart rate.
Fourteen patients with long QT syndrome (aged 26 +/- 16 years, 6 male) and 10 healthy volunteers (aged 37 +/- 11 years, 9 male) underwent graded exercise testing with continuous lead II electrocardiographic monitoring. Long QT patients underwent repeat assessment after 1 month of beta blockade. QT intervals at matching heart rates were compared during exercise and recovery to determine the effect of beta blockade on QT hysteresis, defined as the recovery QT peak interval subtracted from the exercise QT peak interval.
In the 14 long QT syndrome patients, beta blockers slowed the resting heart rate without affecting the corrected QT interval (502 +/- 52 ms baseline vs 481 +/- 40 ms beta blocker, P =.17). The increase in heart rate with exercise was similar in the 3 groups (P =.73). Exaggerated hysteresis of the QT interval was seen in the patients with long QT syndrome at baseline compared with controls (46 +/-19 ms vs 19 +/- 11 ms 1 minute into recovery, P =.006). Beta blockers had minimal effect on the QT interval but markedly reduced hysteresis with minimal separation of the exercise and recovery QT/RR curves (25 +/- 35 ms 1 minute into recovery, P =.027). The combined curve separation at all 6 time points analyzed was 165 +/- 95 ms in patients with long QT syndrome at baseline, 40 +/- 131 ms after beta blockade, and 29 +/- 30 ms in control subjects (P =.002). Comparison of the beta blocker effect on hysteresis in the 2 genotypes suggested a greater reduction in hysteresis in the 3 patients with long QT syndrome 1 compared with the 11 patients with long QT syndrome 2.
Beta blockers reduce QT hysteresis in patients with long QT syndrome to values seen in normal patients. This improved QT adaptation to changes in heart rate may explain the clinical benefit of beta blockers in long QT syndrome.
本研究旨在评估β受体阻滞剂对长QT综合征运动试验运动及恢复阶段QT间期随心率变化的影响。
长QT综合征的特征是在心率突然变化时出现家族性晕厥和猝死。QT间期滞后已被提出作为长QT综合征的一种表型标志物，提示QT间期随心率变化的适应性改变。
14例长QT综合征患者（年龄26±16岁，男性6例）和10名健康志愿者（年龄37±11岁，男性9例）接受分级运动试验，并持续监测II导联心电图。长QT综合征患者在接受β受体阻滞剂治疗1个月后进行重复评估。比较运动及恢复过程中相同心率下的QT间期，以确定β受体阻滞剂对QT间期滞后的影响，QT间期滞后定义为运动QT间期峰值减去恢复QT间期峰值。
在14例长QT综合征患者中，β受体阻滞剂使静息心率减慢，但未影响校正QT间期（基线时为502±52毫秒，β受体阻滞剂治疗后为481±40毫秒，P = 0.17）。三组运动时心率增加情况相似（P = 0.73）。与对照组相比，长QT综合征患者基线时QT间期滞后明显（恢复1分钟时为46±19毫秒 vs 19±11毫秒，P = 0.006）。β受体阻滞剂对QT间期影响极小，但显著降低了滞后现象，运动及恢复阶段的QT/RR曲线分离最小（恢复1分钟时为25±35毫秒，P = 0.027）。在分析的所有6个时间点，长QT综合征患者基线时综合曲线分离为165±95毫秒，β受体阻滞剂治疗后为40±131毫秒，对照组为29±30毫秒（P = 0.002）。比较β受体阻滞剂对两种基因型滞后现象的影响，发现与11例长QT综合征2型患者相比，3例长QT综合征1型患者的滞后现象降低更明显。
β受体阻滞剂可将长QT综合征患者的QT间期滞后降低至正常患者水平。这种改善的QT间期随心率变化的适应性可能解释了β受体阻滞剂在长QT综合征中的临床益处。
