Một sự thay đổi của máu từ epicardium các khu vực thiếu máu cục bộ subendocardial (xem Bảng 10-1). • Giảm dẫn truyền qua nút nhĩ thất (AV) kết quả trong việc làm chậm đáp ứng thất trong rung nhĩ, loạn nhịp trên thất có thể xảy ra ở những bệnh nhân với thiếu máu cục bộ cơ tim. | 162 Cardiac Drug Therapy Preferably carvedilol or metoprolol see text. LV dysfunction diabetes hypertension prior MI silent ischemia asthma that precludes beta-blockers increase the rationale for more urgent coronary angiograms. DPH CA dihydropyridine calcium antagonist only if a beta-blocker is combined with EF 40 ASA acetylsalicylic acid EF ejection fraction LA long acting. Fig. 10-1. Algorithm for the treatment of stable angina. A shift of blood from the epicardium to the subendocardial ischemic area see Table 10-1 . Decreased conduction through the atrioventricular AV node resulting in slowing of the ventricular response in atrial fibrillation or other supraventricular arrhythmias that may occur in patients with myocardial ischemia. Decrease in phase four diastolic depolarization producing suppression of ventricular arrhythmias especially those induced by catecholamines and or ischemia. Increase in ventricular fibrillation VF threshold reduces the incidence of VF and sudden deaths that could at some stage occur in patients with angina see Chapter 1 for other mechanisms . Cardioprotection and Dosage of Beta-Blocker Table 1-4 gives dosages of beta-blockers. The dose of metoprolol is 100-300 mg that of propranolol in nonsmokers is 160-240 mg and that of timolol is 10-20 mg daily 3 4 because these doses have been shown to be effective in preventing sudden death and decreasing total cardiac deaths in well-designed clinical trials 3 15 albeit in patients after MI. The salutary effect of smaller doses is unknown and larger doses are likely to be nonprotective see Chapter 1 3 . Chapter 10 I Management of Angina 163 The dose of beta-blocker is kept within the cardioprotective range to maintain a resting heart rate of 52-60 beats min bearing in mind that no patient should be allowed to have significant adverse effects from medication. If side effects occur the dose is reduced and a nitrate or calcium antagonist is added. If the maximum cardioprotective dose is used and .
