Kaufman E S, Mackall J A, Julka B, Drabek C, Rosenbaum D S
The Heart and Vascular Research Center, Case Western Reserve University, Cleveland 44109, Ohio, USA.
Am J Physiol Heart Circ Physiol. 2000 Sep;279(3):H1248-55. doi: 10.1152/ajpheart.2000.279.3.H1248.
We determined the temporal stability of T wave alternans (TWA) during constant rate stimulation and the dependence of alternans on heart rate (HR) and beta-adrenergic stimulation. Although it is established that exercise can provoke microvolt-level TWA in patients at risk for reentrant ventricular arrhythmias, the mechanisms underlying TWA in humans are not well understood. Specifically, the temporal stability of alternans at any given HR and the influence of HR vs. sympathetic activation on alternans remain unclear. TWA was measured during prolonged fixed-rate atrial pacing at multiple cycle lengths (CLs) in 10 subjects referred for electrophysiological testing and in 14 additional subjects in whom atrial pacing was performed at identical pacing CLs with and without isoproterenol. During constant CL stimulation, TWA amplitude oscillated significantly over time (typically by 10 microV) in a quasiperiodic fashion with periodicity of approximately 2-3 min. Alternans amplitude was strongly dependent on HR but not on adrenergic stimulation. There was a patient-specific threshold HR over which alternans appeared. At higher HR, alternans amplitude increased and oscillations were less prominent. Adrenergic stimulation was required to produce TWA that was not already elicited by moderate elevation of HR in only 2 of 14 (14%) patients. In conclusion, TWA 1) fluctuates spontaneously over 2-3 min and 2) increases monotonically with increased HR (without a major adrenergic contribution in most patients). These data suggest that increased HR rather than sympathetic activation is responsible for arrhythmogenic microvolt-level TWA measured during exercise.
我们测定了恒速刺激期间T波交替（TWA）的时间稳定性，以及交替现象对心率（HR）和β-肾上腺素能刺激的依赖性。虽然已证实运动可诱发折返性室性心律失常风险患者出现微伏级TWA，但人类TWA的潜在机制尚未完全明确。具体而言，在任何给定心率下交替现象的时间稳定性以及心率与交感神经激活对交替现象的影响仍不清楚。在10名接受电生理检查的受试者以及另外14名在相同起搏周期长度（CL）下分别进行有无异丙肾上腺素心房起搏的受试者中，于多个CL下进行长时间固定频率心房起搏时测量TWA。在恒定CL刺激期间，TWA幅度随时间显著振荡（通常为10微伏），呈准周期性，周期约为2 - 3分钟。交替现象幅度强烈依赖于心率，但不依赖于肾上腺素能刺激。存在一个患者特异性的阈值心率，超过该心率会出现交替现象。在较高心率时，交替现象幅度增加且振荡不那么明显。在14名患者中，仅2名（14%）患者需要肾上腺素能刺激才能产生在心率适度升高时未引发的TWA。总之，TWA 1）在2 - 3分钟内自发波动，2）随心率增加单调增加（大多数患者中无主要的肾上腺素能作用）。这些数据表明，心率增加而非交感神经激活是运动期间测得的致心律失常微伏级TWA的原因。
