Acute Mi

Although a recent article challenged this distinction,36 MIs are no longer classified as transmural and subendocardial but as Q-wave and non-Q-wave.36,47-50 In the thrombolytic era, the prevalence of the latter seems to be greater than that of the former (see Chap. 42), presumably due to a reduction in infarct size.42-44 The prethrombolytic "classic" evolution of acute MI has been transformed by pharmacologic therapy and interventional techniques.49,50 The succession of events in the course of a Q-wave MI is from hyperacute positive T waves (on occasion) to ST-segment elevation to abnormal Q waves to T-wave inversion49'50 (&»■□■ Figs. 11-7 and B+-0- JJ^ 8). Commonly, two or more of these findings appear together, depending on the timing of the first recorded static ECG. Acceleration of these phases can occur with effective reperfusion. The time course of ST-segment elevation is a good predictor of reperfusion. Because prethrombolytic 12-lead ECG studies on ST-segment evolutions were based on static recordings obtained at fixed time intervals, it became clear that continuous monitoring in the coronary care unit (which falls outside the realm of this chapter) was essential to adequately record the dynamics of ST-segment trends (Figs. 11-9 and Q+;0; 11-10). Sensitivity increases as frequency of monitoring increases.5153 Continuous monitoring is thus essential to evaluate occurrence of reperfusion. Resolution of ST-segment elevation has been defined as a progressive decrease within 40 to 60 min to less than 50 percent of its maximally elevated value.5152 It has been suggested that in patients treated with thrombolytics, the dichotomization for Q-wave and non-Q-wave MI should be made by the predischarge, rather than the 24-h, ECG due to possible crossover from one group to another.54

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Essentials of Human Physiology

Essentials of Human Physiology

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