Davidenko J M
Department of Pharmacology, SUNY Health Science Center at Syracuse, New York.
J Cardiovasc Electrophysiol. 1993 Dec;4(6):730-46. doi: 10.1111/j.1540-8167.1993.tb01258.x.
Several mechanisms have been proposed to explain the electrocardiographic patterns observed during various forms of polymorphic ventricular tachycardias, including torsades de pointes. Such mechanisms include the coexistence of either multiple foci or multiple exit pathways from single foci giving rise to various forms of aberrant ventricular activation sequences. For example, the simultaneous firing of two widely spaced foci at slightly different frequencies has been used to explain the undulating electrocardiogram that is characteristic of torsades de pointes. However, in spite of some supporting experimental evidence, such an idea remains conjectural from the clinical point of view. Here I discuss a mechanism that has been proposed recently to explain both monomorphic and polymorphic patterns (including undulating patterns) of ventricular tachycardia. The hypothesis is derived from the theory of spiral wave activity in excitable media, and from recent experiments using high resolution optical mapping in isolated two-dimensional ventricular muscle preparations that demonstrate that spiral wave activity may account for self-sustaining reentrant activation. Such studies have led to the observation that the behavior of the spiral center, the core, plays a key role in determining the electrocardiographic manifestation of the arrhythmia. Indeed, a stationary position of the core results in a monomorphic pattern of activation. On the other hand, beat-to-beat changes in the core position (i.e., drifting) leads to irregular patterns of activation. In fact, when drifting occurs in one direction, it gives rise to a Doppler shift in the excitation period in such a way that two coexisting frequencies are manifest, one ahead of and one behind the drifting core. The activation frequency in the region ahead of the core is always higher than that behind the core. Under such conditions, electrocardiographic recordings of the activity demonstrate an undulating pattern, which resembles that of torsades de pointes. When the core drifts in various directions, a polymorphic pattern is manifest. Thus, depending on spiral core dynamics, monomorphic, undulating, or completely irregular patterns may be observed. Moreover, transitions between such patterns can also occur. For example, drifting spirals giving rise to polymorphic activation can become stationary and result in monomorphic activation as a result of anchoring of the core to a small discontinuity (e.g., an artery or small scar) in the tissue. Direct extrapolation of such results to clinical cases is not appropriate. However, the observations discussed in this article offer a new testable hypothesis in which a common mechanism is postulated for the electrocardiographic patterns associated with monomorphic and polymorphic tachycardias.
已经提出了几种机制来解释在各种形式的多形性室性心动过速（包括尖端扭转型室速）期间观察到的心电图模式。这些机制包括多个灶点或单个灶点的多个出口途径并存，从而产生各种形式的异常心室激动序列。例如，两个相距较远的灶点以略微不同的频率同时发放冲动，已被用来解释尖端扭转型室速所特有的起伏心电图。然而，尽管有一些支持性的实验证据，但从临床角度来看，这种观点仍然只是一种推测。在此，我将讨论一种最近提出的机制，该机制可解释室性心动过速的单形性和多形性模式（包括起伏模式）。这一假说源自可兴奋介质中的螺旋波活动理论，以及最近在离体二维心室肌标本上使用高分辨率光学标测的实验，这些实验表明螺旋波活动可能是维持折返激动的原因。这些研究导致观察到螺旋中心即核心的行为在决定心律失常的心电图表现中起关键作用。实际上，核心的静止位置会导致单形性激动模式。另一方面，核心位置的逐搏变化（即漂移）会导致不规则的激动模式。事实上，当核心向一个方向漂移时，它会在兴奋周期中引起多普勒频移，从而表现出两个并存的频率，一个在漂移核心之前，一个在漂移核心之后。核心前方区域的激动频率总是高于核心后方区域。在这种情况下，该活动的心电图记录显示出一种起伏模式，类似于尖端扭转型室速。当核心向各个方向漂移时，就会出现多形性模式。因此，根据螺旋核心动力学，可以观察到单形性、起伏性或完全不规则的模式。此外，这些模式之间也可能发生转变。例如，导致多形性激动的漂移螺旋可能会变得静止，并由于核心锚定在组织中的一个小的不连续处（如一条动脉或小瘢痕）而导致单形性激动。将这些结果直接外推到临床病例是不合适的。然而，本文讨论的观察结果提供了一个新的可检验假说，其中为与单形性和多形性心动过速相关的心电图模式假定了一个共同机制。
