oa Cardiovascular Journal of Africa - Paradigm shift - B-blocker treatment for heart failure
It is well-established that B-blockers, particularly those without intrinsic sympathomimetic activity (lSA), are cardioprotective and prevent secondary recurrences of myocardial infarction (MI) when given within hours of onset of symptoms as well as during late intervention. The reduction in mortality in patients with MI appears significant for those agents without ISA, suggesting that magnitude of reduction in heart rate is an important factor. There is now convincing evidence that B-blockade also produces beneficial effects in 'heart failure (HF). In the early stages of HF, adrenergic support mechanisms help to maintain cardiac output but the long-term effects are deleterious; as a result increased adrenergic drive in HF is directly related to an adverse outcome. Early studies with B-blockers were undertaken primarily in Sweden and subsequently, in the 1980s, the same workers reported beneficial effects of long-term B-blockade with metoprolol in dilated cardiomyopathy. To date, studies have been undertaken with a variety of different B-blockers in patients with idiopathic dilated cardiomyopathy, as well as ischaemic HF. Until the 1990s the results of these studies were inconclusive, but showed a trend towards improvement in congestive HF (CHF). In the past 5 years, several placebo-controlled randomized trials of at least 12 months' duration and involving greater patient numbers have provided more compelling evidence for the use of these agents in CHF. Because cardiac decompensation may occur secondary to their negative inotropic effects, B-blockers are still rarely used in patients with CHF. This has led to the development of B-blockers with vasodilatory effects in an attempt to improve tolerance of these drugs. Initiated gradually, most patients with mild-to-moderate CHF can safely be treated with B-blockers except for some 10 -15% who develop hypotension. Treatment should be initiated in a controlled setting at low doses (carvedilol 6.25 mg twice daily, metoprolol 5 mg twice daily) and titrated upwards gradually. Despite a remarkable reduction in mortality in recent studies with carvedilol, routine management of heart failure with B-blockade can only be recommended when further confirmatory evidence from large, unconfounded randomised clinical trials on an intention-to-treat basis becomes available.
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