cute myocardial infarction resulting from an occlusive thrombus is recognized on an electrocardiogram by ST-segment elevation. 1 Early reperfusion therapy has proved beneficial in such infarctions. 2-4 The earlier the reperfusion, the greater the benefit, and the time to treatment is now considered to indicate the quality of care. These days, when thrombolytic treatment and percutaneous intervention are carried out so readily, it is important to remember that acute infarction is not the only cause of ST-segment elevation. The purpose of this review is to describe other conditions that mimic infarction and emphasize the electrocardiographic clues that can be used to differentiate them from true infarction.

Hemodynamic predictors of myocardial oxygen consumption (MVO 2 ) during static and dynamic exercise were examined in ten normal subjects. Studies were done under the following circumstances: 1) during upright bicycle exercise at an average heart rate of 147 beats/min, 2) during static exercise with an isometric load in the left hand equal to 17% of the maximal voluntary contraction (MVC), and 3) during combined dynamic exercise (average heart rate 147 beats/min) and static exercise using 17% MVC of the left hand. Mean myocardial blood flow (MBF) was 181 ml/100 gm LV/min during dynamic exercise, 98 ml/100 gm LV/min during static exercise, and 201 ml/100 gm LV/min during combined static and dynamic exercise. Addition of a static load to the dynamic load resulted in a higher blood pressure (average 12 mm Hg), MVO 2 and MBF than during dynamic exercise alone. MVO 2 correlated best with products of heart rate and blood pressure regardless of whether the blood pressure was obtained by a central aortic catheter ( r = 0.88) or by a blood pressure cuff ( r = 0.85). When the current data were combined with previous data, 82 determinations of MVO 2 and MBF in 29 normal subjects during several levels of upright exercise were available for analysis. Forty-four determinations were done during dynamic upright exercise, 18 during exercise after propranolol, ten during combined static and dynamic work, and ten during static work alone. MVO 2 correlated best with the product of heart rate and blood pressure ( r = 0.86). Heart rate alone correlated better with MVO 2 ( r = 0.82) than did the tension time index ( r = 0.65) or the product of systolic blood pressure, heart rate, and ejection time ( r = 0.68). The readily measured variables of heart rate and of heart rate x blood pressure correlated well with MVO 2 in normal young men during exercise under a wide variety of circumstances.

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Measurements were made of heart rate, aortic blood pressure, systolic ejection period/beat, myocardial blood flow, and myocardial oxygen consumption in nine normal young men during three bouts of upright bicycle exercise: 1) at the workload which produced a heart rate of 120 beats/minute, 2) at the higher workload necessary to produce a heart rate of 120 beats/minute after administration of intravenous propranolol 0.25 mg/kg, and 3) with infusion of propranolol, at the same workload as the first exercise bout. Comparing exercises 1 and 2, we found a much higher workload was required to produce the same heart rate after propranolol. The blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were the same despite the much greater level of exertion. Comparing exercises 1 and 3, the heart rate, blood pressure, heart rate-blood pressure product, and myocardial oxygen consumption were all significaritly lower during exercise 3 after propranolol despite the fact that the same degree of exercise was being done. As in previous studies, the heart rate-blood pressure product was an excellent correlate of myocardial oxygen consumption despite the change in contractility induced by propranolol. The systolic ejection period was prolonged significantly altering the tensiontime index (TTI), which became an inadequate index of myocardial oxygen consumption. It is concluded that the heart rate-blood pressure product is a good index of myocardial metabolic needs during exercise and the relationship is undistorted by marked changes in contractility, but the tension-time index is a poor correlate. This data emphasizes the fact that the relative metabolic loads for the whole body and for the heart are determined separately and may not change in parallel with a given intervention. Additional Indexing Words:Heart rate Blood pressure Heart rate-blood pressure product Tension-time index Triple product Coronary arteriovenous oxygen difference Exercise Angina T HE RELATIONSHIPS between several readily measured hemodynamic variables and both myocardial blood flow (MBF) and myocardial oxygen consumption (MVO2) in normal subjects