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Twelve-Lead Electrocardiography - part 6

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Tham khảo tài liệu 'twelve-lead electrocardiography - part 6', y tế - sức khoẻ, y học thường thức phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 82 Chapter 9 Myocardial Infarction IIIIII aVRaVLaVF V1 V2 V3 V4V5V6 Figure 9.21. Practice tracing. Practice Tracings The tracings in Figures 9.21 to 9.25 are for practicing your new skills at diagnosing myocardial infarction. The answers may be found at the end of Chapter 14. Figure 9.22. Practice tracing. Practice Tracings 83 Figure 9.23. Practice tracing. Figure 9.24. Practice tracing. Figure 9.25. Practice tracing. 10 Ischemia and Anginal Syndromes Not all instances of diminished coronary artery perfusion result in myocardial infarction. In Chapter 10 we will discuss ECG findings in less than complete coronary artery obstruction. Pathophysiology of Ischemia When arterial perfusion of tissue is inadequate to meet metabolic needs we say that the tissue is ischemic. Metabolic needs in the case of muscle are dependent on the workload of that muscle. In coronary artery disease incomplete obstruction of the coronary arteries with atherosclerotic plaque limits myocardial perfusion. Under circumstances of rest the diminished flow of oxygenated arterial blood may still be sufficient to meet the metabolic needs of the myocardium. However during periods of exercise the needs of the myocardium may require a greater volume of blood than can be delivered through the partially obstructed coronary arteries. In short myocardial oxygen consumption may outstrip oxygen supply. The result is ischemia of the myocardium. Anginal Syndromes If the patient has chest pain in association with ischemia occurring during exercise the syndrome is labeled exertional angina pectoris. Typically when the patient rests the imbalance between oxygen supply and demand resolves and the pain goes away. Exercise is not the only circumstance under which angina can occur however. Any circumstance that increases heart rate or blood pressure for example anxiety or a large meal may increase myocardial oxygen consumption and result in angina. Myocardial ischemia can also occur without producing chest pain. .