Electrocardiogram segments

Acute coronary syndromes Ischemic chest discomfort at rest, most often accompanied by ST-segment elevation, ST-segment depression, or T-wave inversion on the 12-lead electrocardiogram. Furthermore, it is caused by plaque rupture and partial or complete occlusion of the coronary artery by thrombus. Acute coronary syndromes include myocardial infarction and unstable angina. Former terms used to describe types of acute coronary syndromes include Q-wave myocardial infarction, non-Q-wave myocardial infarction, and unstable angina. 

Non-ST-segment elevation A type of myocardial infarction (MI) that is limited to the subendocardial myocardium and is smaller and less extensive than an ST-segment MI. There is usually no pathologic Q-wave on the electrocardiogram in non-ST-segment elevation. 

Patients with variant or Prinzmetal angina secondary to coronary spasm are more likely to experience pain at rest and in the early morning hours. Pain is not usually brought on by exertion or emotional stress nor is it relieved by rest the electrocardiogram (ECG) pattern is that of current injury with ST-segment elevation rather than depression. 

In rabbits burned by an unknown amount of white phosphorus, electrocardiogram alterations (prolongation of QT interval, ST segment depression, T-wave changes, bradycardia, and low voltage QRS complex) indicative of myocardial damage were observed however, no histological alterations were observed in the heart (Bowen et al. 1971). 

A 44-year-old man with no significant cardiac history was given clozapine and 12 days later had bibasal crackles in the chest and ST segment elevation in leads V2 and V3 of the electrocardiogram. He then developed ventricular tachycardia and needed resuscitation. He also developed atrial fibrillation for 24 hours, which subsequently resolved. 

Figure 12.3 Base-apex electrocardiograms from an 11 -year-old horse that presented in congestive heart failure, (a) Before treatment, with ventricular tachycardia (b) Conversion to normal sinus rhythm was achieved with 5 liters 0.64% solution quinidine giuconate, infused at approximately 1 l/h. No specific cause was identified, although echocardiography revealed a segmental area of hypomotile ventricular myocardium, suggestive of ischaemia. The horse was euthanased 3 weeks later after recurrence of the arrhythmia.

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