Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 197

1 In patients with established CAD and angina, β-blockers are first-line therapy as they reduce mortality in the first year after MI (class I). However, in stable CAD without prior MI or HF, or with MI>1 year, there is no evidence of mortality reduction and the main benefit is angina relief.40,41 Without angina, prior MI, or HF, the recommendation for β-blocker therapy is weak (class IIb).

2 A tight rate control <70 bpm has proven beneficial in HFrEF, but not in stable CAD, angina, HTN, AF, or HFpEF.42,43 In fact, in the SIMPLIFY trial, stable CAD patients with baseline pulse >70 bpm (most of whom had MI >3 months prior), did not derive a benefit from slowing the sinus rate with ivabradine, even when angina CCS was ≥II. Thus, tight heart rate control <70 bpm may not need to be pursued in stable CAD with normal EF, except possibly in severe angina.

3 Myocardial β1-receptors have a positive inotropic and chronotropic effect, thus increasing myocardial O2 demands. β2-Receptors mainly have vasodilatory and bronchodilatory effects, with a limited inotropic and chronotropic effect at baseline. However, the latter effect is exaggerated when β1-receptors are blocked. Thus, β2-blockade may be useful in patients requiring a comprehensive blockade of all myocardial adrenergic receptors, such as HF (carvedilol), but may induce harmful vasoconstrictive and bronchospastic effects.

4 Four types of β-blockers:Non-selective β1- and β2-blockers (e.g., propranolol).Selective β1-blockers (e.g., metoprolol, atenolol, bisoprolol). Selectivity is lost at high doses. β-Blockers with intrinsic sympathomimetic activity – β-blockade does not occur at rest, and rather occurs during catecholamine surges; these agents do not decrease mortality and are preferably avoided.β-Blockers with combined α- and non-selective β-blocker activity (carvedilol, labetalol) have a vasodilatory effect and, thus, a more pronounced antihypertensive effect. However, the α-blocking effect gets attenuated with time, particularly with labetalol.⁴⁴

5 ContraindicationsBradycardia <55 bpm or symptomatic bradycardia- PR interval >0.24 s, or any second- or third-degree AV block.Decompensated HF (start β-blockers once HF is compensated).History of clinically severe asthma, even if the patient is currently stable, or actively decompensated COPD with wheezes. A low or moderate dose of a selective β-blocker, such as metoprolol 100 mg/day, may be used in stable, mild/moderate asthma.Use caution in diabetic patients with hypoglycemic episodes.

6 Doses:Metoprolol tartrate 25 mg BID titrated every 3–7 days to a target dose of 50–100 mg BID if tolerated (maximum 200 mg BID). Metoprolol succinate (Toprol XL): the once-daily dose of Toprol XL is almost equivalent to the total daily dose of metoprolol tartrate.Atenolol 12.5–25 mg BID (Qday in renal failure), titrated to 50 mg BID. Carvedilol: 3.125–25 mg BID; labetalol 100–400 mg BID.