Mechanism of exercise-induced hypotension in coronary artery disease

Hypertensive response with exercise does not increase the prevalence of abnormal Tc-99m SPECT stress perfusion images

BACKGROUND

Systemic hypertension and an exaggerated blood pressure (BP) response with exercise have been associated with 'false-positive' findings on stress electrocardiography and echocardiography; however, limited data is available for stress myocardial perfusion imaging (MPI). The purpose of this study was to investigate whether an exaggerated elevation in BP with exercise is associated with an increased prevalence of abnormal MPI.

METHODS

BP responses to exercise were assessed in a cohort of 7,205 patients who underwent stress testing with technetium 99m-SPECT MPI (7/1999-6/2005) for the evaluation of chest pain or dyspnea.

RESULTS

A hypertensive response, defined as a peak systolic BP > or = 220 mmHg, occurred in 355 (4.9%) and was not associated with higher rates of ischemic ECG changes (16.1 versus 16.6%; P = .7), differences in Duke treadmill scores (4.7 +/- 4 versus 5.1 +/- 5; P = .3) or an increased prevalence of abnormal perfusion images (30.1% versus 32.9%; P = .3) to those without a hypertensive exercise response. Patients with a hypertensive response and either intermediate or high-risk MPI (on the basis of summed-difference-scores) referred for coronary angiography, had a high prevalence of coronary artery disease which was similar to those without a hypertensive response (88% versus 83%; P = .5). In an analysis of a community-based patient subset, a hypertensive response was not associated with a difference in either all-cause mortality or subsequent myocardial infarction, coronary revascularization or cardiac death (8% versus 9%; P = .7).

CONCLUSION

A hypertensive BP response to exercise is not associated with increased rates of ischemic ECG changes, higher-risk Duke treadmill scores, greater degrees of abnormal MPI or worse clinical outcome.

Receiver operating characteristic (ROC) curves and the definition of threshold levels to diagnose coronary artery disease on electrocardiographic stress testing. Part I: The use of ROC curves in diagnostic medicine and electrocardiographic markers of ischaemia

A common problem in diagnostic medicine, when performing a diagnostic test, is to obtain an accurate discrimination between 'normal' cases and cases with disease, owing to the overlapping distributions of these populations. In clinical practice, it is exceedingly rare that a chosen cut point will achieve perfect discrimination between normal cases and those with disease, and one has to select the best compromise between sensitivity and specificity by comparing the diagnostic performance of different tests or diagnostic criteria available. Receiver operating characteristic (or receiver operator characteristic, ROC) curves allow systematic and intuitively appealing descriptions of the diagnostic performance of a test and a comparison of the performance of different tests or diagnostic criteria. This review will analyse the basic principles underlying ROC curves and their specific application to the choice of optimal parameters on exercise electrocardiographic (ECG) stress testing. Part I will focus on theoretical description and analysis along with reviewing the common problems related to the diagnosis of myocardial ischaemia by means of exercise ECG stress testing. Part II will be devoted to applying ROC curves to available diagnostic criteria through the analysis of ECG stress test parameters.

A basic approach to the interpretation of the exercise test

To interpret the exercise test, the following parameters need to be evaluated: the heart rate and blood pressure response, symptoms, dysrhythmias, aerobic capacity, and evidence for myocardial ischemia. When analyzing the ST segment for ischemia, the amount and type of ST depression and the time of onset and resolution are examined. The exercise test results are best used to determine a post-test probability that the patient has significant coronary disease, predict its severity, and provide a prognosis of the patient. The test allows primary care physicians to decide which patients with coronary artery disease can be safely managed medically and which high-risk patients need further evaluation and consideration for revascularization.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

Peak exercise blood pressure stratified by age and gender in apparently healthy subjects

OBJECTIVE

To determine the peak blood pressure responses during symptom-limited exercise in a large sample of apparently healthy subjects, including both men and women over a wide range of ages.

DESIGN

We retrospectively studied the blood pressure response during maximal treadmill exercise testing with use of the Bruce protocol in apparently healthy subjects.

MATERIAL AND METHODS

Peak exercise blood pressures in 7,863 male and 2,406 female apparently healthy subjects who underwent a screening treadmill exercise test with the Bruce protocol between 1988 and 1992 were analyzed by age and gender.

RESULTS

In this large referral population of apparently healthy subjects, peak exercise systolic and diastolic blood pressures and delta systolic blood pressure (rest to peak exercise) were higher in men than in women and were positively associated with age. In men, the 90th percentile of systolic blood pressure increased from 210 mm Hg for the age decade 20 to 29 years to 234 mm Hg for ages 70 to 79 years; the corresponding increase among women was from 180 mm Hg to 220 mm Hg. Delta diastolic blood pressure also increased with advancing age. The difference in peak and delta systolic blood pressures between men and women seemed to decrease after age 40 to 49 years. Exercise hypotension, defined as peak exercise systolic pressure less than rest systolic pressure, occurred in 0.23% of men and 1.45% of women and was not significantly related to age.

CONCLUSION

Overall, peak exercise systolic and diastolic, as well as delta systolic, blood pressures were higher in men than in women and increased with advancing age. The reported data will enable clinicians to interpret more accurately the significance of peak exercise blood pressure response in a subject of a specific age and gender and will allow investigators to define exercise hypertension in statistical terms stratified by age and gender.

Comparison of thallium-201 single-photon emission computed tomography and electrocardiographic response during exercise in patients with normal rest electrocardiographic results

OBJECTIVES

This study compared the diagnostic accuracy of exercise thallium-201 single-photon emission computed tomography (SPECT) with the exercise electrocardiographic (ECG) response in patients with normal baseline ECG results.

BACKGROUND

Previous studies comparing exercise thallium imaging with exercise electrocardiography have included patients with abnormal rest ECG results that may have biased the results in favor of thallium imaging.

METHODS

Of 321 patients with a pretest likelihood of coronary artery disease of 70 +/- 29% (mean +/- SD) who underwent exercise stress testing and coronary angiography, 68 had no coronary artery disease; 94 had one-vessel disease; 79 had two-vessel disease; and 80 had three-vessel or left main coronary artery disease.

RESULTS

The diagnostic accuracy of SPECT was higher than that of the ECG response (79% vs. 49%, p < 0.0001). Patients with extensive (left main or three-vessel) coronary artery disease were older and had a lower work load, lower heart rate, greater ST segment depression and more extensive perfusion abnormalities than patients with no disease or one- or two-vessel disease. Multivariate discriminant analysis of exercise and thallium variables identified multivessel thallium abnormalities (F = 35), exercise heart rate (F = 18) and extent of ST segment depression (F = 6) as independent predictors of extensive disease. Of the 80 patients with left main or three-vessel disease, 37 (46%) had > or = 2-mm ST segment depression, 44 (55%) had multivessel SPECT abnormalities, and 61 (76%) had either > or = 2-mm ST depression or multivessel SPECT abnormalities (p = 0.0005 vs. the ECG response; p = 0.01 vs. SPECT).

CONCLUSIONS

In patients with an intermediate to high pretest probability of coronary artery disease and normal baseline ECG results, SPECT is superior to the ECG response in detecting coronary disease. Further, SPECT provides incremental power in identifying patients with extensive (left main or three-vessel) coronary disease.

Mechanism of exercise hypotension in patients with ischemic heart disease. Role of neurocardiogenically mediated vasodilation

BACKGROUND

Exercise-induced hypotension in patients with coronary artery disease (CAD) has been considered to be due to an inability to achieve an adequate increase in cardiac output to match the demands of exercise. We investigated 10 consecutive patients (9 men and 1 woman; age, 38 to 71 years; mean, 52 years) with angiographically documented CAD and exercise-induced hypotension (EIH) (BPPeak < BPRest). Ten approximately age- and sex-matched patients with documented CAD and normal exercise blood pressure response (NBP) served as control subjects.

METHODS AND RESULTS

Nine patients with EIH and all 10 control subjects underwent forearm plethysmography and radionuclide ventriculography (RNV) during semierect cycle exercise. Forearm vascular resistance (FVR) fell by 35 +/- 21% in exercise-induced hypotension patients versus an increase of 78 +/- 65% in patients with an NBP response (P < .0001). Left ventricular ejection fraction increased by 5.1 +/- 7.5% in the group with EIH versus a fall of 4.1 +/- 6.2% in the control group (P = .004). Cardiac output at peak exercise (RNV) increased by 2.2 +/- 0.89-fold in the group with EIH versus 1.49 +/- 0.47-fold in the control group (P = .04). The tenth patient in the group with EIH underwent invasive hemodynamic evaluation during erect exercise. Systolic blood pressure fell (136/80Rest to 50/40Peak) and cardiac output (Fick) tripled, whereas calculated systemic vascular resistance decreased by a factor of 10. Successful angioplasty to an isolated circumflex lesion resulted in resolution of symptoms and abnormal hemodynamic responses during exercise.

CONCLUSIONS

Abnormal vasodilation associated with a normal or even increased rather than decreased cardiac output response appears to be an important mechanism underlying EIH in some patients with CAD. In the present study, this appears to have been the dominant mechanism in 8 and contributory in 2 of the consecutive patients studied.

Exercise induced vasodepressor syncope

Five cases of exercise induced pure vasodepressor syncope in patients without significant structural heart disease are reported. Hypotension and symptoms of syncope or pre-syncope were induced by treadmill exercise testing and in each case limited exercise performance. Evidence of inappropriate peripheral vasodilation, probably as a consequence of ventricular mechanoreceptor stimulation, was shown in all five patients. Head up tilt testing resulted in hypotension in four patients and isoprenaline infusion in the supine position resulted in hypotension in the fifth. These patients had a new condition of exercise induced neurally mediated (vasodepressor) syncope without appreciable structural cardiac abnormalities.

An overview of risk assessment in coronary artery disease

Risk assessment is a central activity in virtually all aspects of the examination and treatment of patients. Methods to standardize this process and improve its accuracy can only improve the quality of medical care. Since health care is undergoing reform in this country, it seems likely that physicians will increasingly need objective justification for their decision making. Risk assessment models offer a potentially useful tool. The Duke Treadmill Score is well-validated and clinically useful for risk assessment in patients with either established or suspected coronary artery disease for whom the desirability of additional invasive testing must be determined. One of the major goals of risk assessment is to identify the low-risk patients for whom no additional testing is required. Whereas multiple valid strategies for accomplishing this exist, there is no consensus on the optimal approach. Cost-containment pressures may indicate the use of exercise testing as the preferred initial strategy in patients who are able to exercise and have an interpretable electrocardiogram. Exercise nuclear testing could thus be reserved for patients in the intermediate-risk group for whom the additional accuracy of these latter tests would provide a more precise risk-stratification estimate. For patients unable to exercise, a pharmacologic stress test (such as echocardiography with dobutamine or an adenosine isonitrile study) would be an acceptable alternative.

The treadmill exercise score revisited: coronary arteriographic and thallium perfusion correlates

The treadmill exercise score has been used to stratify patients into low-, moderate-, and high-risk groups. This score is derived from ST segment depression, angina, and exercise duration. To determine the coronary arteriographic and exercise thallium perfusion correlates of the score, we examined the extent of coronary artery disease and exercise single photon emission computed thallium-201 results in 834 patients for whom cardiac catheterization data were available. Of those, 174 had no coronary artery disease, 195 had one-vessel, 246 had two-vessel, and 219 had three-vessel disease. Based on the treadmill exercise score, 369 were in the low-risk, 384 in the moderate-risk, and 81 in the high-risk group. The extent of coronary artery disease was 2.1 +/- 1 diseased vessels in the high-risk, 1.7 +/- 1 in the moderate, and 1.4 +/- 1.1 in the low-risk group (p < 0.01). The extent of the thallium abnormality (maximum number of abnormal segments 120/patient) was 10 +/- 6 in the high-risk, 7 +/- 6 in the moderate, and 6 +/- 5 in the low-risk group (p < 0.05). Based on the extent of coronary artery disease and results of thallium imaging, patients were reclassified into three groups: group 1 had three-vessel disease and/or > or = 10 abnormal segments (n = 387), group 3 had no coronary artery disease or one-vessel disease and less than five abnormal segments (n = 212), and the remaining patients were in group 2 (n = 235).(ABSTRACT TRUNCATED AT 250 WORDS)