Stable angina treatment. - technical article.
Angina—the pain provoked by myocardial ischaemia—is usually caused by obstructive coronary artery disease that is sufficiently severe to restrict oxygen delivery to the cardiac myocytes. Quality of life is impaired in direct proportion to the severity of symptoms.
Clinical history remains the most useful basis for diagnosis and referral decisions to specialist services, the commonest indications being (1) new-onset angina, (2) exclusion of angina in high-risk individuals with atypical symptoms, (3) worsening angina in a patient with previously stable symptoms, (4) new or recurrent angina in a patient with history of myocardial infarction or coronary revascularization, (5) assessment of occupational fitness (e.g. airline pilots).
Investigation—noninvasive testing is used primarily for diagnosis, but whatever test is employed—exercise ECG, myocardial perfusion imaging, stress echocardiography, or multidetector CT—the incremental diagnostic value is greatest for patients with an intermediate pretest probability of coronary artery disease in whom uncertainty is greatest. Such tests also have a role in risk assessment to inform decisions about the urgency and aggressiveness of treatment in individual cases.
Medical treatment of angina involves (1) dealing with exacerbating comorbidities, (2) secondary prevention by lifestyle modification (smoking cessation, exercise training, Mediterranean-style diet, etc.) and drugs (aspirin, statins, angiotensin-converting enzyme (ACE)-inhibitors, etc.), (3) antianginal drugs (most commonly β-blockers, short acting nitrates, and calcium channel blockers).
Patients with continuing moderate or severe stable angina despite optimal medical treatment should undergo coronary angiography, as should those identified as being at high risk on noninvasive testing. In symptomatic patients, revascularization is generally indicated if one or more of the major coronary arteries—or their large branches—have flow-limiting stenoses (>70% luminal narrowing) or occlusions. Percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG) produce comparable symptomatic benefit. With regard to life expectancy, PCI does not produce survival benefit in patients with stable angina. By contrast, studies more than 20 years ago showed that CABG produced small gains in life expectancy in some patients.
With current management strategies, patients with angina are living longer, but a few remain symptomatic with poor quality of life despite optimal medical treatment and having exhausted revascularization options. Psychological support is important to treat anxiety and depression and improve confidence, and neuromodulatory techniques are sometimes employed.
Angina—the pain provoked by myocardial ischaemia—is usually caused by obstructive coronary artery disease that is sufficiently severe to restrict oxygen delivery to the cardiac myocytes (Bullet list 1). It is the most common initial manifestation of coronary artery disease, the only manifestation that occurs almost as commonly in women as in men, and the only manifestation that is not declining in incidence. When angina occurs in patients without coronary artery disease it may be attributable to other ischaemic mechanisms such as severe anaemia resulting in inadequate oxygen delivery to the cardiac myocytes, or left ventricular hypertrophy secondary to hypertension or aortic stenosis resulting in increased oxygen demand. The appropriately called syndrome X is a diagnosis of exclusion in patients with angina and unobstructed coronary arteries for which there is no clear cause despite full cardiac investigation: abnormal microvascular function is one proposed mechanism, but although symptoms are often resistant to treatment, prognosis is usually good in terms of life expectancy.
Bullet list 1 Causes of angina
- ◆ Coronary artery disease
- • Atherosclerosis
- • Spasm
- • Vasculitic disorders
- • Post radiation therapy
- ◆ Severe anaemia
- ◆ Left ventricular hypertrophy
- • Hypertension
- • Aortic stenosis
- • Aortic regurgitation
- • Hypertrophic cardiomyopathy
- ◆ Right ventricular hypertrophy
- • Pulmonary hypertension
- • Pulmonary stenosis
- ◆ Rapid tachyarrhythmias
- ◆ Syndrome X
In most patients with angina caused by coronary artery disease, quality of life is impaired in direct proportion to the severity of symptoms. Prognosis is often good, particularly in patients with chronic stable symptoms receiving contemporary secondary prevention therapy, but in those with recently diagnosed angina risk is greater, with a 2 to 3% incidence of death or nonfatal myocardial infarction in the first year. Recognition of the need for early investigation has led to the widespread implementation of chest pain clinics both in the United Kingdom and elsewhere to provide patients with suspected angina prompt treatment to relieve symptoms and reduce risk.
Referral for specialist assessment
Referral for specialist assessment (Bullet list 2) is indicated in all patients with known coronary artery disease—particularly those with previous myocardial infarction or coronary revascularization—who experience abrupt worsening of symptoms, often indicating plaque rupture and risk of impending infarction.
Bullet list 2 Angina—indications for specialist cardiological referral
- ◆ New-onset angina
- ◆ Exclusion of angina in high-risk individuals with atypical symptoms
- ◆ Worsening angina in a patient with previously stable symptoms
- ◆ New or recurrent angina in a patient with history of:
- • Myocardial infarction
- • Coronary revascularization
- ◆ Assessment of occupational fitness (e.g. airline pilots)
However, referral decisions may be more difficult in patients presenting for the first time with chest pain. A noncardiac diagnosis accounts for most cases, but it is the task of the primary care or general physician to ensure that all those with suspected angina receive specialist assessment for confirmation of the diagnosis and risk stratification to identify those at greatest risk who need more intensive treatment. As in any screening process, false-negative diagnoses in which patients receive inappropriate reassurance must be avoided. By contrast, a proportion of false-positive diagnoses and referrals is acceptable, and among patients referred from primary care to chest pain clinics 75% have a noncardiac diagnosis.
In primary care, screening is based largely on the character of the symptoms and the age and gender of the patient, other risk factors further helping to identify those with a high probability of coronary artery disease (see below). Access to noninvasive diagnostic tests can be helpful in primary care or the nonspecialist clinic, but there is often insufficient recognition of their limitations, the exercise ECG (for example) having a diagnostic sensitivity of only about 68%, which means that up to one-third of all cases with coronary disease are missed. For this reason, the clinical history remains the most useful basis for diagnosis and referral decisions. Thresholds for referral should be lowered in high-risk patients, including those with previous myocardial infarction and diabetes, and also in airline pilots and public service drivers whose occupations might put others at risk in the event of myocardial infarction or sudden death.
The recommendation that all patients with suspected angina be referred for specialist assessment leaves little room for prevarication. Yet studies repeatedly show inequitable management of patients with chest pain, those with the greatest need often being the very patients who receive the least intensive treatment. Thus elderly patients with chest pain and those of south Asian origin are both high-risk groups, but are less likely than their younger and white counterparts to receive referral to chest pain clinics. Women are also disadvantaged and are less likely than men to be referred, even though it is increasingly recognized that angina in women is almost as common as in men and prognosis little better. The reasons for this inequity are complex and poorly understood, but the consequences for health care are important.
Diagnosis of angina
Angina varies considerably in its clinical presentation and its overlap with other entities can make the differential diagnosis of chest pain difficult. A detailed description of the symptom complex is the most important step in the diagnostic process and in the context of other factors, particularly age and gender, allows the clinician to estimate the probability of coronary artery disease. The extent of work-up required to exclude a noncardiac cause needs to be individually determined. The diagnosis is informed by the clinician’s intuition, experience, and interviewing skills, supported by investigations such as resting ECG, stress testing, and coronary angiography.
A careful history of the character, location, radiation, provocation, and duration of the chest pain provides the most useful diagnostic information. Typically angina is experienced as a constricting, centrally located chest discomfort, radiating to the arms, throat, or jaw, provoked by exertion, less commonly by stress, and relieved by rest usually within 5–10 min. Symptoms are often worse in the morning, shortly after getting up, probably because catecholamine levels and blood pressure peak at this time of day. For similar reasons angina tends to be worse in cold weather and also after a heavy meal. In addition to age and gender, diagnostic probability is also influenced by a family history of premature coronary artery disease and also by other risk factors—particularly diabetes, smoking, hypertension, and dyslipidaemia. Thus, in the patient with chest pain, the probability of coronary disease is very low in men and women under 30, almost regardless of the typicality of the symptoms, while in men and women over 60 with multiple risk factors the probability of coronary disease is high even when the history has atypical features. The experienced clinician makes these probability judgements intuitively in the consulting room and they provide the main basis for the diagnosis of angina.
Despite the reliance on clinical history in making a diagnosis of angina, it can be misleading, with atypical features, such as exertional dyspnoea in the absence of chest pain. Atypical presentations are said to be more common in patients with diabetes but, contrary to popular belief, there is little evidence that this also applies in women and South Asian people.
The physical examination is often normal in the patient with angina but may contribute to diagnosis if signs of major risk factors are identified, particularly hypertension, cutaneous manifestations of dyslipidaemia, and complications of diabetes such as retinopathy and neuropathy. Patients with signs of peripheral vascular disease (e.g. absent pulses, arterial bruits) have associated coronary involvement in most cases.
Simple laboratory investigations may also contribute to diagnosis by identifying groups at heightened risk of coronary disease due to renal dysfunction, dyslipidaemia or diabetes. Anaemia is also important to document because it may cause or—more commonly—exacerbate myocardial ischaemia.
Noninvasive testing is used primarily for diagnosis of coronary artery disease, but also has a role in risk assessment (see below). By tradition, nearly all patients presenting with chest pain have an ECG, although it is of limited diagnostic value. Many patients with angina have a normal recording and, although regional ST segment or T wave changes are commonly associated with coronary disease, only pathological Q waves, reflecting previous myocardial infarction, are diagnostic. Other features of the ECG of potential relevance include tachycardia—particularly in patients with atrial fibrillation—and evidence of left ventricular hypertrophy, either of which may cause or exacerbate myocardial ischaemia.
Diagnostic indications for noninvasive testing depend largely on the level of uncertainty following the clinical assessment. Thus, a 60-year-old man with multiple risk factors who experiences constricting chest pain relieved by rest when he walks up stairs does not need noninvasive testing for diagnostic purposes—he clearly has angina and a negative test would do nothing to change that diagnosis. Similarly, a 25-year-old with transient stabbing pains in the left side of the chest unrelated to exertion does not have angina and a positive test would not modify that diagnostic judgement. These bayesian considerations apply to all noninvasive tests that commonly provide false-positive or false-negative results with little incremental value when the probability of coronary disease based on clinical assessment is respectively very low or very high. Incremental diagnostic value is greatest for patients with an intermediate pretest probability of coronary artery disease (say 10-90%) in whom uncertainty is greatest. In these patients the results of noninvasive testing, positive or negative, can help resolve the uncertainty and contribute to the appropriate further management. The choice of non-invasive test is driven in part by the probability of coronary disease, a low probability (say 10-30%) favouring a test with very high sensitivity such as CT calcium scoring with or without CT angiography, which allows confident rule-out of coronary artery disease if the test is normal. By contrast, when the probability of coronary artery disease is higher (say 30-90%), perfusion imaging or stress echo are usually favoured over the exercise ECG because the specificity of these imaging techniques is higher and an abnormal result strongly suggestive of coronary artery disease.
Once widely used for diagnosis of coronary artery disease, it is now giving way to the newer generation of non-invasive diagnostic tests described below. The sensitivity and specificity of the exercise ECG is 68% and 77% respectively, with diagnostic value tending to be lower in women than in men. The regional development of planar or down-sloping ST segment depression, with gradual recovery when exercise stops, is usually diagnostic, particularly when associated with typical chest pain. The exercise ECG also provides important prognostic information: low exercise tolerance, ST depression early during exercise, an exertional fall in blood pressure, or exercise-induced ventricular arrhythmias all point to an increased risk of myocardial infarction or sudden death. The Duke treadmill score, which takes into account duration of exercise, degree of ST segment deviation, and angina provides a quantitative prognostic assessment and a useful basis for determining the urgency of coronary arteriography.
Myocardial perfusion imaging
This is also widely used for diagnostic purposes and, although more costly and time-consuming than the exercise ECG, has enhanced diagnostic accuracy with a sensitivity and specificity of about 90% for detection of coronary artery disease. Details are described in Chapter 16.3.3. Fixed defects, present at rest and during stress, indicate areas of myocardial infarction. Perfusion imaging also provides useful prognostic information, the extent and severity of perfusion defects (fixed or reversible), the degree of lung uptake of radio-isotope (reflecting level of pulmonary capillary pressure), and the calculated ventricular volume and ejection fraction all predicting risk of future events.
This is used increasingly for diagnostic purposes, but is more dependent than other noninvasive tests on the technical and interpretive skills of the operator. In expert hands it has similar sensitivity to exercise electrocardiography but higher specificity for diagnosing coronary artery disease in patients with suspected angina. Left ventricular imaging during dobutamine infusion permits assessment of regional wall motion in response to adrenergic stress, with decreasing systolic wall motion or wall thickening indicating ischaemia and the likelihood of coronary artery disease.
Multidetector CT (MDCT)
Multidetector (or multislice) CT scanners with up to 64 detectors have sufficient image acquisition speed and spatial resolution to provide noninvasive coronary arteriograms that are becoming comparable to those obtained in the catheter laboratory, as reflected by sensitivity and specificity values of greater than 90% for detection of high-grade coronary stenoses. Unlike conventional coronary arteriography information is also provided about the arterial wall, particularly the severity and distribution of coronary calcification which relates to the severity of coronary atherosclerosis. MDCT provides real promise for delivery of noninvasive coronary arteriography which, if fulfilled, will revolutionize the outpatient assessment of patients with chest pain.
Risk assessment of angina
Recent clinical trials of patients with chronic angina show that aggressive treatment under cardiological supervision reduces risk considerably such that long-term prognosis is good, with all-cause mortality rates of about 1.5% per year. However, prognosis is worse in cohorts attending chest pain clinics in the early weeks or months after symptom onset, with mortality rates in excess of 3% in the first year. Identification of high-risk patients is therefore an important part of the initial assessment to inform decisions about the urgency and aggressiveness of treatment in individual cases.
Clinical indicators of risk
As with diagnosis, it is the clinical assessment that provides the most useful prognostic information in angina. Risk is greatest in patients who are old, those with typical symptoms and—contrary to conventional wisdom—those with more severe symptoms. Women and south Asians, with angina do not appear to be at greater risk. Risk increases with the number of ‘reversible’ risk factors, particularly diabetes, smoking, hypertension, and dyslipidaemia, all of which are important targets for treatment. Risk is also increased in patients with a history of myocardial infarction or stroke. Tachycardia is associated with increased risk, although treatment to slow the heart rate is directed primarily at preventing exertional ischaemia. Heart failure increases risk substantially. The most useful laboratory markers of risk are blood concentrations of lipids (particularly LDL cholesterol and apolipoproteins) and glucose. In patients with renal dysfunction, risk rises in proportion to reduction in creatinine clearance.
Noninvasive testing for risk assessment
Abnormalities of the resting ECG, particularly pathological Q waves and left bundle branch block, are associated with heightened risk in the patient with angina. Other noninvasive tests, including the exercise ECG and isotope perfusion imaging, are also used for risk assessment (see above). Generally speaking, negative test results indicate a good prognosis and a low level of urgency for further invasive investigation. However, when test results suggest severe and extensive ischaemia, risk is often high with important implications for future management.
Many scores have been developed for determining cardiovascular risk in healthy populations and in patients with acute myocardial infarction. Scores are also available for risk assessment in chronic stable angina based on many of the clinical and laboratory variables described above, plus echocardiographic measurement of left ventricular function. As yet, angina risk scores have not found major application in clinical practice.
Invasive testing for risk assessment
In patients with angina, risk of myocardial infarction and cardiovascular death is related to the extent and severity of angiographic coronary artery disease. Risk is particularly high when disease (luminal stenosis >50%) affects all three of the major coronary arteries. In patients with left main coronary artery disease death is inevitable in the event of left main occlusion and urgent revascularization is usually recommended.
A range of inflammatory markers, including C-reactive protein, have been assessed in stable patients with coronary artery disease, but their incremental predictive value for future coronary events is very low once conventional risk factors have been taken into account. Brain natriuretic peptide may be more useful in this group of patients, although currently its main clinical application is in the diagnosis of heart failure.
Treatment of angina
The purpose of treatment is to correct symptoms and reduce risk, thereby improving both the quality of life and its duration.
Comorbidities that exacerbate angina include anaemia, obesity, and thyrotoxicosis, all of which need treating. Most important, however, is hypertension, which increases myocardial oxygen demand in proportion to its severity. Simple lowering of blood pressure will often correct angina without the need for additional symptomatic treatment. Atrial fibrillation is also important because it is common, particularly in elderly patients, and increases myocardial oxygen demand due to tachycardia. Symptom relief can often be achieved by heart rate control or cardioversion. Aortic stenosis is another cause of angina that can be corrected by valve replacement.
The risk of myocardial infarction, stroke, and cardiovascular death can be reduced by lifestyle modification and specific drug therapy. Logic also requires that major atherogenic risk factors—particularly diabetes, smoking, hypertension, and dyslipidaemia—are treated vigorously in patients with angina, evidence for risk reduction being best for blood pressure control, smoking cessation, and LDL cholesterol reduction. Strict glycaemic control in type 2 diabetes, on the other hand, provides little demonstrable protection against cardiovascular endpoints although microvascular complications (renal failure and retinopathy) are effectively diminished. There is some evidence that drugs that increase insulin sensitivity, particularly metformin, may reduce cardiovascular risk in obese people with diabetes, but this requires confirmation in randomized trials.
Evidence-based recommendations are for smoking cessation, exercise training and a Mediterranean-style diet characterized by low intake of total and saturated fats and increased intake of marine or plant ω – 3 fatty acids, fresh fruits and vegetables, and cereals rich in fibre, antioxidants, minerals, vegetable proteins and B group vitamins. Weight reduction in obese patients is also recommended, particularly those with hypertension, dyslipidaemia, or diabetes.
Secondary prevention drugs
All patients with angina should receive aspirin 75–150 mg daily, its antiplatelet activity reducing the thrombotic response to plaque rupture and protecting against myocardial infarction and stroke. Patients intolerant of aspirin despite proton pump inhibition should be treated with clopidogrel, which offers equivalent protection.
Patients with angina should also receive statin therapy to lower LDL cholesterol, thereby reducing lipid accumulation in the arterial wall and stabilizing the atherosclerotic plaque against rupture. Risk reduction is independent of baseline LDL cholesterol concentration, but the more it is lowered the greater the protection against cardiovascular events. At present, therefore, recommendations are to treat to a target of 4 mmol/litre for total cholesterol and 2 mmol/litre for LDL cholesterol. If this cannot be achieved with simvastatin 40 mg (the conventional first line statin in the United Kingdom), the dose needs increasing or a more potent statin such as atorvastatin or rosuvastatin needs to be substituted. In patients who cannot be treated to target or who are unable to tolerate statins, ezetimibe is usually added (or substituted) to reduce cholesterol absorption from the bowel, although there is no current evidence of prognostic benefit. The cardiovascular risk attributable to low HDL is well established, but it is not yet known if treatment to increase HDL with nicotinic acid derivatives is beneficial in patients with coronary artery disease.
Angiotensin converting enzyme (ACE) inhibition provides additional protection against cardiovascular endpoints in patients with angina, evidence being best for high-risk subgroups such as elderly patients, those with diabetes, and those with previous myocardial infarction. However, given the extended indications for these drugs in hypertension, diabetes, and left ventricular dysfunction, most patients with angina are suitable candidates for treatment. The mechanism of benefit with ACE inhibition may extend beyond blood pressure reduction, there being evidence for anti-inflammatory and antiproliferative effects which inhibit the atherogenic process and stabilize coronary plaques.
β-Blockers, though widely used for symptomatic treatment, have no clear evidence-based indication for secondary prevention in patients with angina unless there is associated left ventricular dysfunction, when prognostic benefit is well established. Antioxidant vitamins C and E have failed the test of clinical trials for secondary prevention in coronary artery disease. Similarly, there is no role for hormone replacement therapy for protecting against coronary events in postmenopausal women.
Drugs used to treat angina reduce ischaemia by improving the balance between myocardial oxygen supply and demand. Guideline recommendations are that medical therapy with antianginal drugs should be tried before angioplasty or surgery is considered, except in those patients with stable angina with left main stem or multivessel coronary disease in whom there is evidence that surgical revascularization might improve prognosis.
The three most widely used groups of antianginal drugs are β-blockers, nitrates, and calcium channel blockers. A meta-analysis of randomized trials concluded that β-blockers should be considered the first line treatment, but in clinical practice the three groups of drugs are used with approximately equal frequency, often in combination when benefits are additive.
These drugs reduce myocardial oxygen demand, principally by slowing the heart rate, although reductions in left ventricular wall tension (blood pressure) and contractility also contribute. Choice of β-blocker is largely determined by patient acceptability, with preference given to once-daily cardioselective agents such as atenolol or bisoprolol. Effective relief of exertional angina can often be obtained without recourse to other drugs if the heart rate response to exercise can be reduced sufficiently. There is a clear indication for β-blockers when angina occurs in patients with heart failure or asymptomatic left ventricular dysfunction. They are usually well tolerated, but noncardiac side effects, particularly fatigue and erectile dysfunction, may be troublesome even with cardioselective agents. β-Blockers are contraindicated in patients with bronchial asthma.
These drugs improve myocardial oxygen delivery and reduce demand by direct coronary and peripheral vascular dilatation. Sublingual glyceryl trinitrate by tablet or spray should be given to all patients with angina, rapid absorption through the buccal mucosa providing symptomatic relief within 3 min. It can also be used prophylactically to prevent angina during exertion. Long-acting isosorbide mononitrate for regular oral administration is widely used, although variable tolerance to its therapeutic action may occur. Side effects are rarely troublesome apart from headache during the first few days of treatment.
Like nitrates, these are vasodilators and improve myocardial oxygen balance by their effect on coronary flow and peripheral resistance. Angina complicated by hypertension provides a clear indication for drugs of this class when amlodipine is usually the preferred agent. Diltiazem and verapamil are also useful because, in addition to vasodilator activity, they often produce minor reductions in heart rate, although combination therapy with β-blockers is best avoided. Nifedipine, which tends to increase heart rate, is not recommended for treatment of angina. Side effects of calcium blockers are related to vasodilatation and include facial flushing, postural dizziness, and mild ankle oedema.
Potassium channel openers
Nicorandil is the only drug in this group licensed to treat angina. It is a vasodilator with effects comparable to those of long-acting nitrates. The principal side effect is headache.
This interesting compound is licensed for treatment of angina in a number of European countries (not the United Kingdom). Its pharmacological effects are metabolic, not haemodynamic, with coupling between glycolysis and carbohydrate oxygenation restored by shifting cardiac energy metabolism from oxygenation of fatty acids (the preferred myocardial substrate) to glucose, thus preserving intracellular ATP levels. Antianginal effects are comparable to other agents and are additive to those of β-blockers and calcium blockers. Side effects, including gastrointestinal disturbance, are rarely troublesome.
This recently licensed compound inhibits the If channel in the sinus node, reducing the slope of diastolic depolarization and slowing the heart rate. The effect of ivabridine on heart rate is comparable to that of β-blockers, but because If channels are largely restricted to the heart and the retina blood pressure is unaffected and many of the noncardiac effects of β-blockers, particularly fatigue and erectile dysfunction, do not occur. Mild visual side effects tend to resolve during treatment. Antianginal efficacy appears to be comparable to β-blockers and calcium blockers and the drug is now licensed for treatment of angina in patients with normal sinus rhythm (rate reduction does not occur in atrial fibrillation) who have a contraindication to or intolerance of β-blockers.
This newly developed agent now has a licence for use in chronic angina where other antianginals have been inadequate. Its mechanism of action has not been fully characterized but appears to involve inhibition of the late inward sodium channel which indirectly prevents calcium overload of ischaemic myocytes and reduces diastolic wall tension and oxygen demand. Heart rate or blood pressure are unaffected. Antianginal effects are additive to those of β-blockers and calcium blockers. Side effects including constipation and dizziness are rarely troublesome.
In the patient with angina, revascularization provides a nonpharmacological means of improving myocardial oxygen delivery by restoring coronary flow to the ischaemic myocardium. More than 60% of all revascularization procedures in stable angina are now by percutaneous intervention (PCI) using balloon angioplasty and stenting. The remainder are by coronary artery bypass surgery (CABG), the choice depending largely on the extent and severity of coronary artery disease. At present, this can only be determined by coronary angiography which is an essential prerequisite of revascularization in the management of angina.
Which patients with stable angina should undergo coronary angiography?
This question has received little attention from clinical trialists, but guideline recommendations are for angiography in patients with continuing moderate or severe angina despite optimal medical treatment. Other groups for whom angiography is recommended include those identified as being at high risk on noninvasive testing (see above), those who have been successfully resuscitated from sudden cardiac death or who have life-threatening ventricular arrhythmias. Occasionally angiography is indicated in asymptomatic patients with suspected or known coronary artery disease whose jobs (e.g. piloting aircraft, driving public service vehicles) are dependent on a normal or fully revascularized coronary circulation. It may also be indicated in patients unwilling or unable to take antianginal drugs, or those in whom there is important diagnostic uncertainty despite noninvasive investigation.
Choice of revascularization procedure—CABG vs PCI
In symptomatic patients who have undergone cardiac catheterization, revascularization is generally indicated if one or more of the major coronary arteries—or their large branches—have flow-limiting stenoses (>70% luminal narrowing) or occlusions. The choice of revascularization procedure is dependent on a range of factors:
- ◆ Coronary anatomy—historically, PCI has been preferred for single-vessel and two-vessel coronary artery disease and CABG for more extensive disease. This preference has been based largely on evidence of prognostic benefit for CABG in patients with three-vessel or left main stem disease (see below), but also on technical factors, particularly the relative inefficacy of PCI in total coronary occlusions and in densely calcified lesions when coronary dissection or failure of adequate dilatation have been commonplace. However, the evidence for prognostic benefit in three-vessel or left main stem disease derives from trials performed more than 30 years ago and their contemporary relevance is uncertain. Moreover, technological developments, including drills and stents, and improvements in operator technique, now allow successful procedures in many cases that until recently were considered exclusively surgical. Choice of procedure is therefore now less dependent on anatomical considerations, and more on operator experience and patient preference.
- ◆ Patient preference—PCI is often preferred because it avoids surgery, requires no more than 48 hours hospitalization (day case PCI is now feasible) and permits early return to normal activities within a few days of the procedure.
- ◆ Procedural risk—mortality is lower for PCI than CABG (0.9% vs 2.2%). Stroke risk is also lower but rates of nonfatal myocardial infarction are comparable.
- ◆ Symptomatic benefit—this is comparable for PCI and CABG, but recurrence of symptoms and need for repeat revascularization is higher for PCI because of coronary restenosis in the months following a successful procedure. Indeed restenosis has been the Achilles heel of PCI, and until the introduction of coronary stents affected 30% or more of all patients. Since then stenting has become widespread, producing more effective coronary patency although reductions in rates of restenosis to less than 10% had to await the introduction of drug-eluting stents that deliver antiproliferative drugs (e.g. sirolimus, paclitaxel) locally within the coronary artery. The prospect of providing long-term relief of symptoms without the need for repeat procedures has considerably enhanced the clinical value of PCI.
- ◆ Prognostic benefit—to date there have been no studies showing survival benefit for PCI in patients with stable angina. For CABG, small gains in life expectancy have been reported in patients with left main stem coronary disease, three-vessel disease and two-vessel disease with severely stenosed proximal left anterior descending artery. These reports, however, are from studies more than 30 years ago and their contemporary relevance may have changed with advances both in surgical techniques and in medical therapy. Indeed it is generally accepted that improvements in the prognosis of coronary artery disease in the last 25 years have little to do with revascularization, but much to do with lifestyle changes and advances in secondary prevention therapy.
Management of refractory angina
With current management strategies patients with angina are living longer, but a proportion, perhaps 5 to 10%, remain symptomatic on optimal medical treatment, having exhausted revascularization options. These patients commonly have extensively collateralized coronary circulations and well-preserved left ventricular function such that prognosis is not worse than other patients with angina, but the quality of life is poor because of refractory symptoms. Psychological support is important to treat anxiety and depression and improve confidence. Options for further antianginal therapy, however, are limited.
Stellate ganglion block has a time-honoured role in the treatment of refractory angina, local anaesthetic injection interrupting sensory traffic from the myocardium with variable relief of symptoms. Repeated treatments are available for responders.
Transcutaneous electrical nerve stimulation (TENS) finds application in a variety of acute and chronic pain syndromes. Its use is not based on any well-substantiated therapeutic mechanism, but some patients find it helpful.
Spinal cord stimulation (SCS) also finds application in a variety of pain syndromes without a well substantiated therapeutic mechanism. Clinical trials confirm that SCS reduces myocardial ischaemia with amelioration of symptoms in patients with refractory angina, but because effective blinding is impossible placebo effects may contribute significantly to clinical benefit.
Enhanced external counterpulsation (EECP) works on the same principle as the intra-aortic balloon pump. Pressure cuffs applied to the lower limbs are inflated sequentially during diastole, resulting in augmented diastolic central aortic pressure and increased coronary perfusion pressure. Compression of the vascular bed of the legs also increases venous return and cardiac output. Rapid and simultaneous decompression of the cuffs at the onset of systole permits systolic unloading and decreased cardiac workload. Clinical benefit has been reported, but again the contribution of placebo response is hard to quantify.
A single study of autologous bone marrow cells injected via the coronary sinus produced variable benefit in patients with refractory angina. More studies are needed to determine whether this treatment will have a useful clinical role.