Number 24, 2004
Angina Pectoris

Risk stratification in chronic stable angina

Back to the Summary

Mario Marzilli
Division of Cardiology and Postgraduate School of Cardiology, University of Siena School of Medicine, Siena, Italy
Correspondence: Prof Mario Marzilli, Cardiologia Universitaria, Policlinico Le Scotte, Viale Bracci, 53100 Siena, Italy.
Tel: +390577585374, fax: +390577233112, e-mail: marzilli@unisi.it

Introduction
Since the Framingham Heart Study, algorithms have been developed to stratify patients in low, intermediate, and high risk categories in order to relate the intensity of diagnostic and treatment strategies to risk category [1–2].
Changes in population risk profile and identification of novel risk factors, in addition to documentation of new preventive measures, all necessitate a continuous update of diagnostic and therapeutic procedures. Consequently, testing algorithms and guidelines are continuously being refined on the basis of new research [3–4].

Diagnosis of angina pectoris
A detailed history, focused physical examination, and risk factor assessment provide the clinician with an estimate of the probability of coronary heart disease [5].
If the diagnosis remains uncertain, exercise testing should be performed. Interpretation of the exercise test includes symptomatic response, exercise capacity, hemodynamic response, and ECG response. In patients who are unable to exercise or present with abnormalities in the resting ECG, an echocardiographic or nuclear stress imaging study is recommended [6–7].
For imaging the coronary artery lumen, coronary angiography remains the most accurate technique.

Risk stratification
The prognosis of patients with chronic stable angina and a normal resting ECG and low clinical risk for severe coronary artery disease is excellent.
Clinical parameters that are independent predictors of three-vessel disease or left main coronary artery disease include age and sex, typical angina, diabetes, and previous myocardial infarction. A 5-point cardiac risk score has been developed that is based on these parameters, and patients found to be at a high likelihood of severe disease may be directly referred for angiography.
Other clinical parameters relevant to prognosis include history of hypertension, hypercholesterolemia, smoking, and peripheral arterial disease.
Patients with chronic stable angina with resting ECG abnormalities, or cardiomegaly or pulmonary venous congestion on chest X-ray are at greater risk.

Left ventricular function
Left ventricular global systolic function and volumes are important prognostic factors in patients with cardiac disease, including those with chronic stable angina. Left ventricular ejection fraction is an important measure of left ventricular systolic function, and can be obtained with echocardiography or radionuclide imaging.
In patients with chronic stable angina and with previous myocardial infarction, assessment of systolic and diastolic left ventricular function becomes relevant to the choice of appropriate treatment and in making recommendations about lifestyle, work activity, etc [5].
In patients with signs or symptoms of heart failure, cardiac imaging is necessary to identify the mechanism of the cardiac disease and determine the most appropriate therapy.

Stress testing for risk stratification and prognosis
Maximum exercise capacity remains one of the strongest and most consistent prognostic markers and may be measured as maximal exercise duration, maximum metabolic equivalent of task units achieved, maximum workload achieved, maximum heart rate, and double product [6].
Exercise-induced ST-segment depression or elevation summarize the prognostic information related to ischemia. Other variables, including angina, number of leads with ST-segment shift, pattern of ST-segment shift, and time to recovery of ST-segment deviation, are less powerful prognostic indicators [6].
A patient's performance and ECG changes may be combined to calculate risk and predict mortality. Annual cardiac mortality is predicted by the Duke Treadmill Score: [exercise time in minutes (5 times the ST-segment deviation in millimeters)] minus (4 times the angina index), where the angina index is: 0 for no angina, 1 for angina, and 2 if angina is the reason for stopping the test). Patients with a predicted mortality rate ≤1% can be managed medically; those with a risk ≥3% should be referred for cardiac catheterization. Patients with intermediate risk should undergo either cardiac catheterization or an imaging study.
The standard treadmill ECG remains the best choice for coronary risk stratification in men with normal resting ECG and capable of exercise. A normal stress echocardiogram in patients with known or suspected coronary heart disease confers a favorable prognosis. In patients with an intermediate risk, myocardial perfusion imaging appears to be of value for further risk stratification [6].

Imaging studies for risk stratification
The exercise test remains the most appropriate test for risk stratification and assessment of treatment in patients with chronic stable angina. It provides useful information on patient symptoms, cardiovascular function, and hemodynamic response during daily activity.
In patients who cannot exercise adequately, various types of pharmacological stress combined with imaging techniques are available.

Myocardial perfusion imaging
Stress myocardial perfusion single-photon emission computed tomography (SPECT), or myocardial perfusion scan, provide clinically useful information in patients with a high pre-test likelihood of coronary artery disease [7–9].
A normal stress thallium test is associated with a rate of cardiac death and myocardial infarction of 0.5% to 0.9% per year, which is close to that of the general population, even in patients with known coronary artery disease. In patients with a normal thallium stress test, the likelihood of significant coronary artery disease is so low that coronary angiography is not indicated unless the patients has a high Duke Treadmill Score.
Rates of cardiac death and myocardial infarction increase significantly with worsening scan abnormalities, particularly in the setting of severely abnormal scans. Other scintigraphic findings predictive of adverse events include cavity dilatation, ejection fraction and end-systolic and end-diastolic volumes, and post-stress myocardial stunning. Patients with severe perfusion defects and low ejection fraction are at greatest risk for subsequent events [10–11].

Stress echocardiography
Stress echocardiography is routinely used for the diagnosis of coronary heart disease in patients with angina, and is a sensitive and specific alternative to stress thallium for detecting inducible myocardial ischemia and for risk stratification [12]. The annual cardiac event rate increases as a function of the extent and severity of abnormal contractile response during stress, expressed as wall motion score index (WMSI) [13]. A normal contractile response (peak WMSI=1.0) is associated with a favorable prognosis (0.9% per year), whereas mild-to-moderate dysfunction (peak WMSI=1.1–1.7) and severe dysfunction (peak WMSI greater than 1.7) are associated with increasing rates of cardiac events (3.1% per year and 5.2% per year, respectively). The prognostic value of ejection fraction is additive to WMSI (Figure 1), ejection fractions less than 45% being associated with a high cardiac event rate, even in patients with mild contractile dysfunction during stress. A peak WMSI greater than 1.7 associated with ejection fractions less than 45% identifies patients at greatest risk of adverse events. The prognostic value of WMSI and ejection fraction are also confirmed by data on cumulative survival at 40 months (Figures 2, 3).

Invasive testing for risk stratification
Patients identified as being at increased risk on the basis of clinical evaluation and noninvasive testing are generally referred for coronary angiography.
Coronary angiography is not a reliable indicator of the functional significance of a coronary stenosis and does not allow prediction of which coronary lesion will eventually cause an acute coronary event. Conversely, the extent and severity of coronary disease and left ventricular dysfunction are powerful predictors of long-term patient outcome. Several prognostic indexes based on coronary angiography have been proposed, the most popular being classification as 1-, 2-, or 3-vessel, or left main coronary artery disease.
Catheterization laboratory derived measures of the severity of coronary stenosis show a good relationship with myocardial perfusion imaging in the population with single-vessel disease [15–17], but the comparability of the two approaches is low in multivessel disease, for which nuclear or echocardiographic techniques retain higher prognostic power [18–19].

Risk stratification after coronary revascularization
In asymptomatic patients, routine stress testing for risk stratification is not useful and may be harmful [20–21]. However, coronary atherosclerosis is a progressive disease, and recurrent cardiac events are to be expected even after a successful procedure.
Recurrence of chest pain within 6 months after coronary revascularization constitutes an indication to repeat coronary angiography (Figure 4). When angina recurs after the time interval of possible restenosis, the exercise stress test regains its diagnostic and prognostic role.

Back to the Summary

REFERENCES

Back to the Summary