Coronary artery disease, hypertension, and diabetes are by far the main causes of heart failure in the developed world; rheumatic heart disease, infection and malnutrition are the most common causes in the developing world.
Problems in defining the etiology of heart failure
A meta-analysis of several trials identified ischemic heart disease as the main cause of heart failure in 68% of cases. Crucial determinants in such prevalence figures are the inclusion and exclusion criteria consistently used in the trials concerned, in particular ages and a low ejection fraction. Thus, a common entry criterion for heart failure studies is a reduction in left ventricular systolic function, expressed as an ejection fraction <35% to 40%. This systematically excludes patients with less impaired left ventricular systolic function. Ischemic heart disease was the causal factor of heart failure in 40% of the 20 000+ patients included in the Italian Network-Congestive Heart Failure (IN-CHF) registry; yet 30% had an ejection fraction >40%. The exclusion of such patients underestimates both the incidence of heart failure and the prevalence of ischemic heart disease in its etiology.
The proportion of patients with ischemic heart failure varies substantially between studies. The prospective Framingham study using biennial history, electrocardiography, and noninvasive examination found evidence of coronary artery disease in 42% of men and 25% of women predating heart failure. However, more recent studies using different techniques have found an even higher prevalence of ischemic heart failure, eg, 61% (68% in men and 38% in women) in a noninvasive surveillance study in Eastern Finland. The similarly noninvasive Hillingdon Heart Failure Study in London found the prevalence to be 36%, but declared the etiology unknown in 34%; it is not unlikely, had invasive methods been used, that the bulk of the unknown etiology group would have been reclassified in the ischemic group, perhaps to a total as high as 60%. Noninvasive methods are inadequate for determining the true prevalence of ischemic heart failure.
Coronary angiography is probably the gold standard diagnostic test for ischemic heart disease. Provocative tests of myocardial ischemia can be less sensitive due to the low stress level achieved, and also less specific. This may be due to difficulty in reading the electrocardiogram, which is often distorted by intraventricu-lar conduction delays and impaired ventricular repolarization at rest; it can also be due to the frequent ambiguity in the echocardiographic features associated with hypokinetic dilated ventricles and in the myocardial perfusion images of cardiomyopathic ventricles. Clinical assessment without angiography underestimates the proportion of patients with coronary artery disease, and fails to identify those who may benefit from revascularization.
Once ischemic heart disease is diagnosed, it must be decided whether it is the cause of heart failure. This confirms the importance of coronary angiography and the need for a comprehensive, and not solely anatomical, approach to the diagnosis of ischemic heart failure. Fox et al recendy identified all incident cases of heart failure in a population of 292 000 in South London by monitoring admissions to hospital and to a rapid-access heart failure clinic. Coronary angiography was used to identi- fy the presence and severity of coronary artery disease in patients under 75 years. It was defined as the primary etiology in the absence of angiography data in patients with a documented history of an acute ischemic syndrome or stable angina with evidence of reversible ischemia on exercise testing or myocardial perfusion imaging. Coronary artery disease was identified as the cause of 52% of cases of incident heart failure in the general population under 75 years, an incidence very similar to that recorded in the Hillingdon Heart Failure Study which used a similar methodology to demonstrate an incidence of 0.8 cases per 1000 population per year. Angiography and myocardial perfusion imaging revealed 30% of these cases to have significant coronary artery disease. Sixty-five percent either had significant hibernation justifying possible revascularization or underwent revascularization prior to myocardial perfusion imaging. The finding of coronary artery disease has treatment implications in addition to revascularization. Aspirin, and in particular lipid-lowering therapy, should be initiated to prevent coronary events and deterioration in left ventricular function. Thus, the recent studies identify coronary artery disease as the single most important cause of heart failure. In the absence of cardiac catheterization or myocardial perfusion imaging, its prevalence is underestimated. In addition, significant hibernating myocardium may be present in patients in whom it is clinically silent.
Trends in heart failure have changed in recent decades. In the Framingham study, coronary artery disease was the primary cause in 22% of patients in the 1950s, 36% in the 1960s, 53% in the 1970s, and 67% in the 1980s. Over the past 30 years, the mortality rate from ischemic heart disease has more than halved, while in the 1990s it has declined by 2% to 6% per year. Nevertheless, in 1990, ischemic heart disease accounted for 6.26 of the 50.68 million deaths worldwide (29%) and this percentage is expected to rise to 36% in 2020. As for heart failure, both incidence and prevalence have increased exponentially over the last few decades, probably due in part to the lower mortality from ischemic heart disease, and in part to population aging. Because the incidence of ischemic heart disease is not declining in the Western world, and is increasing in the developing countries, and because the elderly are increasing in number, the prevalence of ischemic heart failure can be predicted to increase markedly over the next few decades unless countered by revolutionary preventive or therapeutic strategies.
pathophysiology; coronary artery disease; etiology; cardiomyopathy; ischemic heart disease; epidemiology
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