International Task Force for Prevention of
Coronary Heart Disease
CORONARY HEART DISEASE: REDUCING THE RISK
Patients with CHD often suffer from stroke and vice versa. Because stroke and CHD have several risk factors in common, many measures aimed at reducing CHD incidence might be expected to reduce the incidence of stroke too. The value of antihypertensive treatment in preventing stroke has now been established beyond reasonable doubt. In addition, there is increasing evidence that the lipid-lowering statin drugs reduce the incidence of stroke.
In Western countries, ischaemic stroke is much more common than the haemorrhagic variety (about 4:1). Recognised mechanisms underlying ischaemic stroke are embolism to the brain of cardiac or aortic origin, artery-to-artery embolism from extra-cranial and intracranial arteries and, rarely, perfusion failure due to severe extra-cranial arterial stenosis and occlusion. In persons with hypertension the most frequent cause of stroke is occlusion of small cerebral arteries. Non-modifiable risk factors for ischaemic stroke are age (the stroke rate more than doubles every 10 years after the age 55), male sex (although stroke incidence is higher in men, more strokes occur in women than in men every year because of greater life expectancy in women), race (mortality from stroke is higher among Blacks than among Whites) and inherited predisposition. In addition, persons of Asian origin, notably the Chinese, Koreans and Japanese, have a very high stroke incidence. The well-documented modifiable risk factors for stroke are hypertension (the single most important cause of stroke), diabetes mellitus, cardiac diseases (atrial fibrillation, infective endocarditis, mitral stenosis, recent large myocardial infarction, left ventricular hypertrophy), cigarette smoking (produces an almost twofold increase in relative risk of stroke), overweight (particularly central adiposity), elevated alcohol consumption (associated in particular with increased risk of haemorrhagic stroke in men consuming four or more drinks per day) and elevated plasma homocysteine levels.
The relationship between cholesterol levels and stroke has been controversal since studies that do not differentiate between ischaemic and haemorrhagic stroke have often observed no such relationship. But when these types of stroke are distinguished, it is evident that the incidence of ischaemic stroke increases with increasing plasma cholesterol levels; on the other hand, the incidence of intracerebral haemorrhage appears to be highest at very low cholesterol levels especially in hypertensives. Haemorrhagic stroke is considerably rarer than ischaemic stroke in Caucasian populations. In the prevention of stroke, effective treatment of hypertension is the centrally important measure.
Total stroke incidence was decreased also in several recent trials of cholesterol lowering by statin drugs. Possible mechanisms include stabilisation of atherosclerotic plaques in the thoracic aorta and the carotid arteries so lessening the risk of embolism, reduced number of coronary revascularization procedures and a lower incidence of cardiac arrhythmias.
Other modifiable risk factors for stroke include an elevated haematocrit and increased levels of fibrinogen and tissue-type plasminogen activator inhibitor. The use of illicit drugs (especially cocaine), physical inactivity, obesity and the presence of anti-phospholipid antibodies have also been shown in some studies to be associated with stroke.
Haemorrhagic stroke includes-intracerebral (ICH) and subarachnoidal haemorrhage (SAH). The former is twice as common as the latter in population-based computer tomographic studies. Major risk factors for ICH are high blood pressure, advanced age, race (higher incidence in Blacks), male sex, heavy use of alcohol, cocaine use, and anticoagulant or thrombolytic therapy. Amyloid angiopathy is also a cause of stroke in the elderly. Cigarette smoking and hypertension are major risk factors for subarachnoid haemorrhage. In addition, subarachnoid haemorrhage is often due to rupture of congenital or acquired aneurysms or angiomatous malformations.
1.4.1 Primary and secondary prevention of stroke
Effective treatment of hypertension reduces the incidence of stroke and fatal stroke by about 40%. Treatment is also effective in elderly people with isolated systolic hypertension, even after 80 years of age. Smoking cessation is beneficial at all ages, even in light smokers. Diabetes and obesity require treatment, including lifestyle modifications such as diet and physical activity. In studies on the effects of statins in secondary prevention of CHD, an approximate 30% reduction of stroke incidence was observed 4.
In patients with atrial fibrillation, anticoagulant therapy with warfarin reduces the risk of ischaemic stroke by almost 70%. In doses of at least 325 mg per day, acetyl salicylic acid reduces the risk of stroke in atrial fibrillation by between 10 and 20%. Treatment of left ventricular hypertrophy and valve disease also reduce stroke incidence, as does surgical treatment of patent foramen ovale.
Acetyl salicylic acid and ticlopidine are of value in the secondary prevention of ischaemic stroke, and reduce the risk of a completed stroke by approximately 20% 5. However, the benefit of antiplatelet drugs in primary prevention of stroke is unproven. The present consensus is that carotid endarterectomy should be performed in patients with a stenosis of the internal carotid artery of at least 70% who have suffered a corresponding transient ischaemic attack or minor stroke within the previous 6 months. Surgery should also be considered for asymptomatic but severe carotid stenosis.