Sinh lý bệnh của thiếu máu cục bộ Khi động mạch tưới máu mô là không đủ để đáp ứng nhu cầu trao đổi chất, chúng ta nói rằng mô là thiếu máu cục bộ. Chuyển hóa nhu cầu, | 118 Chapter 13 Miscellaneous Conditions potassium begin to produce lengthening PR intervals and nonspecific but often dramatic QRS widening. P waves begin to flatten and may disappear altogether. The terminal event is asystole or ventricular fibrillation. Figure is the ECG of a 52-year-old white male seen in the emergency department with a serum potassium of mEq L on the basis of renal failure and diabetic ketoacidosis. Note that P waves cannot be seen in most leads and there is diffuse nonspecific widening of the QRS to over s. Figure is a tracing taken on the same patient after treatment with intravenous calcium gluconate bicarbonate and insulin. Note that although clear P waves Figure A. Severe hyperkalemia. ECG of a 52-year-old white male with renal failure and diabetic ketoacidosis and a serum potassium of . P waves are absent and the QRS is widened to over . B. ECG of the same patient as in Figure but after treatment with IV calcium gluconate insulin and sodium bicarbonate. Digitalis Effect 119 have not yet returned the QRS has dramatically narrowed and T waves in V4 and V5 have taken on the tall peaked appearance typical of lower levels of hyperkalemia. As with hypokalemia ventricular fibrillation may be the ultimate consequence of progressive hyperkalemia. Common causes of hyperkalemia include renal failure acidosis administration of aldosterone antagonists and administration of exogenous potassium. Hypocalcemia The hallmark of hypocalcemia is a prolonged QT interval. Occasionally T wave inversion will also occur but this is unusual. Clinically significant hypocalcemia is rare and the primary cause is usually hypoparathyroidism. Hypercalcemia Elevations of serum calcium produce the opposite to those produced by hypocalcemia namely a shortened QT interval often with a very abrupt upslope of the T wave. Hypercalcemia is more common than hypocalcemia. Major causes include advanced malignancy hyperparathyroidism and .