The prognostic value of exercise capacity: a review of the literature

The use of a questionnaire and simple exercise test in the preoperative assessment of vascular surgery patients

We aimed to assess the reliability of patients as historians in terms of the self assessment of functional capacity and also examined the usefulness of a simple ward exercise tolerance test. One hundred consecutive elective vascular surgery patients were interviewed preoperatively using a modified Duke Activity Status Index (DASI) questionnaire. To test reliability in reference to an independent observer, the questionnaire concerning the patient was also applied to each patient's closest relative who was blinded to the patient's responses. Patients were then asked to walk up two flights of stairs and the time taken to complete the task or the reason for failing to complete the task was recorded. The D

Cardiac risk assessment for noncardiac surgery: current concepts

Strategies for perioperative risk assessment in patients undergoing noncardiac surgery vary among physicians and are aimed to estimate the risk and minimize complications. We propose simplistic guidelines for assessing and modifying risk for patients undergoing a wide variety of procedures.

Exercise performance-based outcomes of medically treated patients with coronary artery disease and profound ST segment depression

OBJECTIVES

We sought to determine the relationship between exercise duration and cardiovascular outcomes in patients with profound (> or =2 mm) ST segment depression during exercise treadmill testing (ETT).

BACKGROUND

Patients with stable symptoms but profound ST segment depression during ETT are often referred for a coronary intervention on the basis that presumed severe coronary artery disease (CAD) will lead to unfavorable cardiovascular outcomes, irrespective of symptomatic and functional status. We hypothesized that good exercise tolerance in such patients treated medically is associated with favorable long-term outcomes.

METHODS

We prospectively followed 203 consecutive patients (181 men; mean age 73 years) with known stable CAD and > or =2 mm ST segment depression who are performing ETT according to the Bruce protocol for an average of 41 months. The primary end point was occurrence of myocardial infarction (MI) or death.

RESULTS

Eight (20%) of 40 patients with an initial ETT exercise duration < or =6 min developed MI or died, as compared with five (6%) of 84 patients who exercised between 6 and 9 min and three (3.8%) of 79 patients who exercised > or =9 min (p = 0.01). Compared with patients who exercised < or =6 min, increased ETT duration was significantly associated with a reduced risk of MI/death (6 to 9 min: relative risk [RR] = 0.25, 95% confidence interval [CI] 0.08 to 0.76; >9 min: RR = 0.14, 95% CI 0.04 to 0.53). This protective effect persisted after adjustment for potentially confounding variables. We observed a 23% reduction in MI/death for each additional minute of exercise the patient was able to complete during the index ETT.

CONCLUSIONS

Optimal medical management in stable patients with CAD with profound exercise-induced ST segment depression but good ETT duration is an appropriate alternative to coronary revascularization and is associated with low rates of MI and death.

Exercise testing in clinical medicine

Exercise-induced changes in the electrocardiogram have been used to identify coronary artery disease for almost a century. Over the past decade, however, clinicians have increasingly focused on more expensive diagnostic tools believing them to offer improved diagnostic accuracy. In fact, by incorporating historical data, the simple exercise test can in most cases outperform the newer tests. The use of prediction equations and non-staged exercise protocols can improve the test still further, while advances in the use of the test for prognosis, with the discovery of novel risk factors and the addition of gas analysis, may in the future shift the primary emphasis away from diagnosis. Brief, inexpensive, and done in most cases without the presence of a cardiologist, the exercise test offers the highest value for predictive accuracy of any of the non-invasive tests for coronary artery disease.

Disparate effects of improving aerobic exercise capacity and quality of life after cardiac rehabilitation in young and elderly coronary patients

PURPOSE

Although cardiopulmonary exercise variables predict prognosis, functional capacity, and quality of life (QoL) in patients with coronary artery disease (CAD), these variables have not been assessed fully before and after exercise training in elderly with CAD. Therefore, the purpose of this study was to determine the impact of formal Phase II cardiac rehabilitation and exercise training programs on cardiopulmonary variables and QoL in elderly and younger CAD patients.

METHODS

The authors analyzed consecutive patients before and after Phase II cardiac rehabilitation and exercise training programs, and compared exercise cardiopulmonary data and data from validated questionnaires assessing QoL (MOS SF-36) and function in 125 younger patients (< 55 years; mean 48 +/- 6 years) and 57 elderly (> 70 years; mean 78 +/- 3 years).

RESULTS

At baseline, elderly patients had lower estimated aerobic exercise capacity (-27%; P < 0.001), peak oxygen consumption (VO2) (-19%; P < 0.01), and anaerobic threshold (-10%; P < 0.05), as well as total function scores (-11%; P < 0.01) and total QoL scores (-5%; P = 0.06). Commonly used prediction equations greatly overestimated aerobic exercise capacity compared with precise measurements using cardiopulmonary testing both before (+23% and +12% in younger and elderly patients, respectively) and after the exercise training programs (+51% and +31% in younger and elderly patients, respectively), and more so in younger compared with older patients. After rehabilitation, the elderly had significant improvements in estimated aerobic exercise capacity (+32%; P < 0.0001), peak VO2 (+13%; P < 0.0001), anaerobic threshold (+11%; P = 0.03), total function scores (+27%; P < 0.0001), and total QoL scores (+20%; P < 0.0001). Although younger patients had greater improvements in estimated aerobic exercise capacity (+44% versus +32%; P = 0.08), peak VO2 (+18% versus +13%; P < 0.01), and anaerobic threshold (+17% versus +11%; P = 0.07), the elderly had statistically greater improvements in both function scores (+27% versus +20%; P = 0.02), and total QoL scores (+20% versus +14%; P = 0.03).

CONCLUSIONS

These data confirm the benefits of precisely determining aerobic exercise capacity by cardiopulmonary function, especially to determine the benefits of an exercise training program. In addition, these data using cardiopulmonary exercise tests and validated assessments of quality of life demonstrate the disparate effects of cardiac rehabilitation programs on improvements in aerobic exercise capacity and QoL in young and elderly with CAD.

Ramp exercise protocols for clinical and cardiopulmonary exercise testing

Historically, the protocol used for exercise testing has been based on tradition, convenience or both. In the 1990s, a considerable amount of research has focused on the effect of the exercise protocol on test performance, including exercise tolerance, diagnostic accuracy, gas exchange patterns and the accuracy with which oxygen uptake (VO2) is predicted from the work rate. Studies have suggested that protocols which contain large and/or unequal increments in work cause a disruption in the normal linear relation between VO2 and work rate, leading to an overprediction of metabolic equivalents. Other studies have demonstrated that such protocols can mask the salutary effects of an intervention, and some have suggested that the protocol design can influence the diagnostic performance of the test. Guidelines published by major organisations have therefore suggested that the protocol be individualised based on the patient being tested and the purpose of the test. The ramp approach to exercise testing has recently been advocated because it facilitates recommendations made in these guidelines. This article reviews these issues and discusses the evolution of ramp testing which has occurred in the 1990s.

Guidelines for perioperative cardiac evaluation from the American College of Cardiology/American Heart Association task force are effective for stratifying cardiac risk before aortic surgery

PURPOSE

We assessed whether the American College of Cardiology/American Heart Association (ACC/AHA) task force guidelines for perioperative cardiac evaluation could reliably stratify cardiac risk before aortic surgery.

METHODS

We retrospectively applied the guidelines to a closed database, set up prospectively. The setting was a referral center in an institutional practice with hospitalized patients. The closed database included 133 patients who had a routine cardiac examination, which comprised an estimation of functional capacity and noninvasive testing, before aortic surgery. This cardiac evaluation led to the proposal of coronarography in 23 patients and to treating an underlying coronary artery disease in 21 patients (including three myocardial revascularizations). One patient died after myocardial revascularization, and two patients died of cardiac causes after aortic surgery. The algorithm of the ACC/AHA guidelines was applied independently by two investigators to each patient's file that was included in the existing database. The main outcome measure was a comparison between cardiac risk stratification with the ACC/AHA guidelines and the results of the routine cardiac evaluation.

RESULTS

The ACC/AHA guidelines were successfully applied to all 133 files by the two investigators. After applying the algorithm, 73 patients were stratified as low cardiac risk, and 60 patients were stratified as high risk. The 21 patients who had undergone a preoperative coronary artery disease optimization were stratified as high risk by means of the ACC/AHA guidelines. The patients who died from cardiac causes were stratified as high risk by means of the ACC/AHA guidelines, whereas none of the patients stratified as low risk died during hospitalization.

CONCLUSION

The ACC/AHA guidelines were effective in stratifying cardiac risk by using clinical predictors and an estimate of the physical capacity of the patient. Their use may allow a reduction in unnecessary noninvasive testing in patients stratified as being at low risk, while permitting the selection of all patients likely to benefit from preoperative coronary artery disease optimization.

Cardiopulmonary exercise testing and prognosis in severe heart failure: 14 mL/kg/min revisited

BACKGROUND

Accurately establishing prognosis in severe heart failure has become increasingly important in assessing the efficacy of treatment modalities and in appropriately allocating scarce resources for transplantation. Peak exercise oxygen uptake appears to have an important role in risk stratification of patients with heart failure, but the optimal cutpoint value to separate survivors from nonsurvivors is not clear.

METHODS

Six hundred forty-four patients referred for heart failure evaluation over a 10-year period participated in the study. After pharmacologic stabilization at entrance into the study, all participants underwent cardiopulmonary exercise testing. Survival analysis was performed with death as the end point. Transplantation was considered a censored event. Four-year survival was determined for patients who achieved peak oxygen uptake values greater than and less than 10, 11, 12, 13, 14, 15, 16, and 17 mL/kg/min.

RESULTS

Follow-up information was complete for 98.3% of the cohort. During a mean follow-up period of 4 years, 187 patients (29%) died and 101 underwent transplantation. Actuarial 1- and 5-year survival rates were 90.5% and 73.4%, respectively. Peak ventilatory oxygen uptake (VO(2)) was an independent predictor of survival and was a stronger predictor than work rate achieved and other exercise and clinical variables. A difference in survival of approximately 20% was achieved by dichotomizing patients above versus below each peak VO(2) value ranging between 10 and 17 mL/kg/min. Survival rate was significantly higher among patients achieving a peak VO (2) above than among those achieving a peak VO (2) below each of these values (P <.01), but each cutpoint was similar in its ability to separate survivors from nonsurvivors.

CONCLUSION

Peak VO (2) is an important measurement in predicting survival from heart failure, but whether an optimal cutpoint exists is not clear. Peak VO(2) may be more appropriately used as a continuous variable in multivariate models to predict prognosis in severe chronic heart failure.

Technetium Tc 99m sestamibi myocardial perfusion imaging: current role for evaluation of prognosis

Like 201Tl imaging, technetium Tc 99m sestamibi (MIBI) myocardial imaging can be used with exercise and pharmacologic testing to assess the presence of coronary artery disease. An increasing body of literature indicates that MIBI can also be used to assess risk of future cardiac events such as myocardial infarction or death. This article summarizes the current status of MIBI imaging for evaluating prognosis in patients with known or suspected coronary artery disease.

The treadmill test--where to stop and what does it mean?

The prognostic utility of an exercise ECG test depends upon having an adequate workload to stress the cardiac system. A negative stress test, in which there are no adverse clinical or ECG findings, and in which an adequate workload is achieved, stratifies patients into a low-risk group. The 1997 American Heart Association guidelines imply that any index of workload--heart rate, rate-pressure product, or exercise duration in multiples of resting O2 consumption (METS)--could be used to indicate that adequate stress was achieved. However, while there is considerable evidence supporting the use of METS as a strong independent prognostic variable, there is less support for the use of rate-pressure product or heart rate. Indeed, there is evidence that a high heart rate at a low workload carries an adverse prognosis. Further research is needed to identify the number of METS achieved that would define an adequate workload. In the meantime, a review of the literature suggests that 7 to 10 METS is a reasonable ballpark figure of the minimum workload in patients with a negative stress test that would imply a favorable outcome.

Perioperative Risk Stratification in Patients Undergoing Noncardiac Surgery

Adverse cardiac events during noncardiac surgery are a major cause of morbidity and mortality. As the population ages, greater numbers of patients (including the elderly) are undergoing noncardiac surgical procedures; additional emphasis must therefore be placed on effective preoperative risk assessment. On a national level, the estimated annual expenditure for this process is already $3.7 billion. There is a need for both the specialist and primary care provider to execute a safe, methodical, and cost efficient screening plan. This process should identify both the patients at highest risk and also those at lowest risk. Subsequently, the emphasis should attempt to minimize the overall risk of perioperative complications. The cornerstone of risk assessment requires meticulous history taking, a thorough physical examination, and usually a chest radiograph and an ECG. Five subsequent (basic) steps for the evaluation of patients for noncardiac surgery are outlined here in assessment of clinical markers and the pa- tient's functional capacity, risk of the surgical procedure, the need for noninvasive testing, and when appropriate, the indications for invasive testing. The AHA/ACC Practice Guidelines Committee has outlined a clinical algorithm which provides a stepwise approach to guide the clinician during the decision making process. The purpose of preoperative evaluation is not to "give medical clearance" per se, but rather to evaluate the patient's current medical status, detect stress-induced ischemia in a cost effective manner, and to make recommendations about patient management throughout the entire perioperative period.

Clinical determinants in perioperative cardiac evaluation

Perioperative cardiac events are the largest cause of morbidity and mortality for patients undergoing elective surgery. As a result, numerous recent studies have focused on attempts to identify patients at increased risk for perioperative events. These have delineated testing modalities capable of identifying high-risk patients, and clinical markers which further stratify patients facing elective surgery into high-, medium-, and low-risk subgroups. In this article, the authors review the evidence supporting the use of clinical markers of risk to evaluate patients before elective surgery. The role of preoperative clinical assessment in identifying patients most likely to benefit from further testing or intervention, (ie, those at significant risk for short- and long-term cardiac events) is stressed. Assessment and intervention for risk factors of long-term cardiac disease is also stressed, as the preoperative evaluation represents an opportunity for improvement in the short- and long-term cardiac risk profile. Finally, the algorithm for preoperative cardiovascular evaluation published jointly by the ACC/AHA joint taskforce on practice guidelines is reviewed. This algorithm is a synthesis of the current literature, into a cost effective and efficient approach to patient evaluation.

The role of the cardiology consultant: putting it all together

Consultation represents the act of providing advice regarding diagnosis and/or management and may comprise a major component of a cardiologist's practice. A frequent cause for cardiac consultation is preoperative risk assessment. With steadily decreasing morbidity and mortality related to noncardiac surgery, cardiovascular management strategies that are known to improve long-term outcomes should guide decision making in the perioperative setting. The preoperative cardiac consultation may represent an opportunity to initiate or modify cardiac care including primary and secondary preventive measures. A stepwise approach to perioperative cardiac risk assessment, as set forth by joint American College of Cardiology and American Heart Association guidelines, should be employed. The hallmark of successful preoperative cardiology consultation is effective communication with referring physicians. A consultant's good clinical judgement will only impact a patient's care if recommendations are communicated effectively. There is no substitution for direct, verbal contact. Recommendations should be kept to less than five when possible, be brief and specific. The consultant should provide contingency plans and follow-up. Good consultative technique increases compliance with recommendations and facilitates efficient patient care.

The effects of body composition changes to observed improvements in cardiopulmonary parameters after exercise training with cardiac rehabilitation

STUDY OBJECTIVE

To discriminate the effects of body fat reduction on improvements in peak aerobic capacity made following exercise training during cardiac rehabilitation.

DESIGN

Observational, prospective study.

SETTING

Outpatient cardiovascular health center at regional academic center. PATIENT INTERVENTIONS: Peak oxygen uptake (pkVO2), percent body fat, lean body mass (LBM), and other anthropometric measures were assessed before and after a 3-month program of cardiac rehabilitation and exercise training in 500 consecutive cardiac patients following a major coronary event. Baseline pkVO2 was corrected for LBM (pk/VO2 lean) and compared with posttraining values.

RESULTS

Following exercise training, percent body fat decreased 5% from 26.2+/-8.0 to 24.8+/-7.5 (p<0.0001), and LBM increased 1% from 61.3+/-12.5 to 61.7+/-11.8 kg (p=0.02). pk/VO2 increased 16% from 16.0+/-4.1 to 18.5+/-4.8 mL/kg/min (p<0.0001), and pkVO2 lean increased 13% from 21.7+/-5.3 to 24.6+/-6.0 mL/kg/min (p<0.0001). Isolating the effects of reduction in body fat, we discern that these changes contributed to 0.3 of the 2.5 mL/kg/min increase in pkVO2 or 12% of the increase in pkVO2 observed.

CONCLUSIONS

Changes in body composition, as a consequence of dietary and exercise modification, contribute to 12% of the "observed" improvement noted in weight-adjusted peak aerobic capacity following cardiac rehabilitation and exercise training. Changes in pkVO2 lean should be used by investigators to assess the singular effects of exercise conditioning alone.

Perioperative cardiac evaluation for noncardiac surgery noninvasive cardiac testing

Prognostic risk stratification to identify perioperative and long-term cardiac risk in selected patients undergoing noncardiac surgery is part of good clinical practice. Exercise variables associated with significant increased risk include poor functional capacity (eg, <4 metabolic equivalents), marked exercise-induced ST segment shift or angina at low workloads, and inability to increase or actually decrease systolic blood pressure with progressive exercise. Approximately 40% of patients tested before peripheral vascular surgery will have an abnormal exercise electrocardiogram (ECG). The predictive value for a perioperative event, ie, death or myocardial infarction, ranges from 5% to 25% for a positive test and 90% to 95% for a negative test. Whereas exercise cardiac imaging is the modality of choice in patients with a noninterpretable exercise ECG, pharmacological stress imaging should be used in the 30% to 50% of patients who require perioperative noninvasive risk stratification and are unable to perform an adequate level of exercise to test cardiac reserve. Myocardial perfusion variables predictive of increased cardiac events include severity of the perfusion defect, number of reversible defects, extent of fixed and reversible defects, increased lung uptake of thallium-201, and marked ST segment changes associated with angina during the test. The reported sensitivity and specificity of dobutamine-induced echocardiographic wall motion abnormalities in patients with peripheral vascular disease is similar to myocardial perfusion scintigraphy, but the confidence limits are wider due to the smaller sample size in these more recent studies. In conclusion, noninvasive cardiac testing should be used selectively in patients undergoing noncardiac surgery; the results provide useful estimates of short- and long-term risk of cardiac events, and the magnitude of abnormal response on noninvasive testing should be used to formulate decisions regarding the need for coronary angiography and subsequent revascularization.

Disparate effects of out-patient cardiac and pulmonary rehabilitation programs on work efficiency and peak aerobic capacity in patients with coronary disease or severe obstructive pulmonary disease

BACKGROUND

Exercise intolerance is an integral component of chronic obstructive pulmonary disease (COPD) and coronary heart disease (CHD) and is caused by several mechanisms that ultimately impact overall functional capacity. We assessed various components of exercise function in patients with CHD and COPD during the course of cardiac and pulmonary rehabilitation to evaluate changes unique to each condition.

METHODS

Work efficiency (WEf, defined as delta watts/delta VO2) and peak VO2 were measured and compared at baseline and after 3 months (36 sessions) of outpatient cardiac and pulmonary rehabilitation programs in 25 patients (mean age = 66 +/- 7 years) with severe COPD (mean FEV1.0 = 0.90 +/- 0.35 L) and in 25 patients (mean age = 65 +/- 8 years) with CHD.

RESULTS

At baseline, patients with COPD had significantly reduced values of WEf (2.04 +/- 0.86 versus 3.23 +/- 1.38 watts/mL/kg/min; P = 0.004) and peak VO2 (13.2 +/- 3.9 versus 17.1 +/- 3.9 mL/kg/min; P = 0.005) compared with patients with CHD. After rehabilitation, patients with CHD increased peak VO2 by 12% (17.1 +/- 3.9 to 19.1 +/- 4.9 mL/kg/min; P = 0.01) with no change in WEf (3.23 +/- 1.38 to 3.32 +/- 1.43 watts/mL/kg/min; P = not significant). In contrast, patients with COPD increased peak VO2 by only 5% (13.2 +/- 3.9 to 13.9 +/- 3.8 mL/kg/min; P = 0.0008), but WEf increased by 36% (2.04 +/- 0.86 to 2.78 +/- 0.84 watts/mL/kg/min; P = 0.0002). Subjective measures of functional status improved similarly in both groups.

CONCLUSIONS

In contrast to patients with CHD, work inefficiency contributes significantly to exercise intolerance in patients with severe COPD. Outpatient rehabilitation programs enhance functional status in patients with CHD and COPD by differing mechanisms, depending on the underlying disease. These data show the disparate effects of out-patient rehabilitation on peak VO2 and WEf in cardiac and pulmonary patients.

A Therapeutic Commentary

ABSTRACT: Thirty-one million patients in the United States undergo surgical procedures every year. Approximately 10%-the majority of these with hypertension-are at an increased risk for perioperative and postoperative cardiovascular morbidity and mortality. Thus, hypertensive patients requiring surgery, especially the 2.1 million undergoing noncardiac procedures, should be evaluated carefully for the magnitude, and if severe, the cause of the hypertension. Additionally, their associated metabolic and cardiovascular status should be characterized and corrected with aggressive therapy. Hypertensive patients with known ischemic heart disease, those with multiple risk factors for ischemic heart disease (IHD), some with valvular heart disease, and those with congestive heart failure should be evaluated for their ability to perform the physical and social activities of everyday life, and, when necessary, have formal stress testing. Most studies suggest that blood pressures of 180/110 mm Hg or greater are associated with a greater risk for perioperative ischemic events. Therefore, the goals of blood pressure control should be to reduce the blood pressure without jeopardizing organ function. Antihypertensive medication should be administered until the time of surgery. beta-Receptor blockers should be instituted or continued in patients with angina and in some patients with congestive heart failure. Those without prior antihypertensive therapy might be best treated with beta-blocker therapy perioperatively as evidenced by the Multicenter Study of Perioperative Research Group with atenolol and those earlier studies with metoprolol. The risks of the surgery should be discussed with the patient so the risks can be weighed against the expected benefit. Studies suggest that perioperative risk for any patient, and especially patients with hypertension, are in part related to the adrenergic arousal before, during, and after the procedure as evidenced by the rise in heart rate and blood pressure, along with the liberation of clotting facators and increased risk for plaque rupture, coronary vasoplasm, and consequent myocardial infarction and fibrosis.

Importance of estimated functional capacity as a predictor of all-cause mortality among patients referred for exercise thallium single-photon emission computed tomography: report of 3,400 patients from a single center

OBJECTIVES

We sought to determine the relative influence of estimated functional capacity and thallium-201 (Tl-201) single-photon emission computed tomographic (SPECT) findings on prediction of short-term all-cause and cardiac-related mortality.

BACKGROUND

Decreased functional capacity and abnormal Tl-201 SPECT findings are predictive of increased cardiovascular risk and mortality. However, the relative importance of these variables as predictors of all-cause mortality is not well established.

METHODS

Analyses were based on 3,400 consecutive adults undergoing symptom-limited exercise Tl-201 SPECT testing at the Cleveland Clinic Foundation between September 1990 and December 1993; none had previous invasive procedures, heart failure or valve disease. Estimated functional capacity, classified by age and gender, and thallium perfusion defects, expressed as a stress extent thallium score on a 12-segment scale, were analyzed to determine their relative prognostic importance during 2 years of follow-up.

RESULTS

Of 3,400 patients, 108 (3.2%) died during follow-up; 32 deaths were identified as cardiac related. On univariable analysis, estimated functional capacity was a strong predictor of death, with 62 (57%) deaths occurring in patients achieving < 6 metabolic equivalents (METs) (log-rank chi-square 86, p < 0.0001). On multivariable analysis, the strongest independent predictors of all-cause mortality were fair or poor functional capacity (adjusted relative risk [RR] 3.96, 95% confidence interval [CI] 2.36 to 6.64, chi-square 27, p < 0.0001) and age (adjusted RR for 10 years 2.25, 95% CI 1.80 to 2.80, chi-square 27, p < 0.0001). The presence of SPECT thallium perfusion defects was a less powerful predictor of death (for each two additional segments with defects, adjusted RR 1.21, 95% CI 1.03 to 1.43, chi-square 5, p = 0.02). Cardiac mortality was predicted by both fair or poor functional capacity (adjusted RR 4.37, 95% CI 1.59 to 12.00, chi-square 8, p = 0.004) and by stress extent thallium score (adjusted RR 1.62, 95% CI 1.25 to 2.11, chi-square 13, p = 0.0003).

CONCLUSIONS

In this clinically low risk group, estimated functional capacity was a strong and overwhelmingly important independent predictor of all-cause mortality among patients undergoing exercise Tl-201 SPECT testing. The extent of myocardial perfusion defects was of comparable importance for the prediction of cardiac mortality.

Comparison of maximum versus submaximum exercise testing in providing prognostic information after acute myocardial infarction and/or coronary artery bypass grafting

Exercise testing after acute myocardial infarction (AMI) provides prognostic information. In many studies submaximum exercise tests performed until a given work load, metabolic equivalents (METs) level, or heart rate were used or patients discontinued the exercise test prematurely because of symptoms. We showed recently that peak oxygen uptake during maximum exercise provides independent prognostic information in patients with coronary artery disease. It is, however, not known whether maximum exercise testing is superior in predicting mortality than testing until a target level. Second, it is unclear which target end point best classifies patients at increased risk. Therefore, the independent relation between mortality and indexes of, respectively, maximum and submaximum exercise capacity, were analyzed in 527 patients, who were tested until exhaustion. To express submaximum exercise capacity dichotomous variables (the ability to reach a target METs level or not), and a continuous variable relative to maximum exercise capacity (the ventilatory anaerobic threshold) were used. After adjustment for significant covariates, peak oxygen uptake was significantly related to all-cause and cardiovascular mortality. The target level of 5 METs and the ventilatory anaerobic threshold, when expressed in absolute workload, were related to mortality when unadjusted, but after adjustment for age and other confounders significancy was lost. In multiple Cox regression analysis, the prognostic power of peak oxygen uptake remained significant when 5 METs or the anaerobic threshold were forced into the equations. When analyzing the relation of various METs levels with mortality, the 7 METs level was independently related to all-cause and cardiovascular mortality and yielded the highest diagnostic accuracy. We conclude that maximum exercise testing is more potent in predicting mortality than the ability to reach a predetermined level of exercise, such as the commonly used 5 METs level or the anaerobic threshold. Otherwise, the use of a higher target level of 7 METs is recommended.

Is computer interpretation of the exercise electrocardiogram a reasonable surrogate for visual reading? Veterans Affairs ACME Investigators

BACKGROUND

Interpretation of exercise tests as positive or negative is primarily based upon exercise-induced ST segment changes. Consistently accurate measurements are difficult to obtain during exercise.

HYPOTHESIS

This study compared on-line computer-generated electrocardiographic (ECG) analysis with visual interpretation. The goals were to document the extent of agreement, establish reasons for disagreements, characterize ST-segment depression (extent, onset, duration), and determine the sensitivity and ability to localize coronary artery disease for each method.

METHODS

Comparisons were made in 120 patients at eight Veterans Affairs Medical Centers. An exercise test was considered positive if > 1.0 mm horizontal or downsloping ST-segment depression was detected 0.08 s after the J point during exercise or recovery. The ST-segment depression had to be present on at least two successive ECG recordings 15 s apart. Computer interpretation was based on median averaged beats.

RESULTS

There was an 88% agreement of visual and computer interpretations [106/120 (both positive, n = 62; both negative, n = 44)]. The disagreements involved visual negative, computer positive in 10 cases and visual positive, computer negative in 4 cases. Correlation was excellent between methods for characterization of ST-segment depression (p < 0.0001). Sensitivity for detecting and the ability to localize coronary artery disease (> or = 70% stenosis) were similar for both methods.

CONCLUSION

This computer algorithm using median averaged beats is a reasonable surrogate for visual interpretation of the exercise ECG, making it a valuable source of confirmation of physician readings in large research trials and in clinical settings.

Prognostic significance of peak oxygen uptake in hypertension

The aim of this study was to investigate the prognostic value of cardiopulmonary fitness in hypertension. From 1972 to 1982 oxygen uptake and heart rate were recorded during an exercise test to exhaustion in 216 patients (143 men). Their outcome was ascertained in 1994. During 3,411 patient years of follow-up, 53 patients suffered at least one fatal or nonfatal cardiovascular event and 25 patients died. After adjustment for age, gender, and weight, the relative hazard rates (RHR; Cox regression) of peak oxygen uptake (l.min-1) amounted to 0.44 (P = 0.01) for the first occurring cardiovascular events and 0.35 (P = 0.05) for all-cause mortality. These RHR remained significant after additional adjustment for traditional cardiovascular risk factors (RHR = 0.45 and 0.28, respectively; P < 0.05). Heart rate at 50 W did not predict outcome after adjustment for age and gender (P = 0.94 and 0.14, respectively), nor after additional adjustment for heart rate at rest (P = 0.86 and 0.61, respectively). In conclusion, a lower peak oxygen uptake, but not a higher submaximal heart rate, is significantly and independently associated with a higher incidence of cardiovascular events and a higher total mortality in hypertensive patients.

Predicting functional capacity during treadmill testing independent of exercise protocol

Clinically useful estimates of VO2max from treadmill tests (GXT) may be made using protocol-specific equations. In many cases, GXT may proceed more effectively if the clinician is free to adjust speed and grade independent of a specific protocol. We sought to determine whether VO2max could be predicted from the estimated steady-state VO2 of the terminal exercise stage. Seventy clinically stable individuals performed GXT with direct measurement of VO2. Exercise was incremented each minute to optimize clinical examination. Measured VO2max was compared to the estimated steady-state VO2 of the terminal stage based on ACSM equations. Equations for walking or running were used based on the patient's observed method of ambulation. The measured VO2max was always less than the ACSM estimate, with a regular relationship between measured and estimated VO2max. No handrail support: VO2max = 0.869.ACSM -0.07; R2 = 0.955, SEE = 4.8 ml.min-1.kg-1 (N = 30). With handrail support: VO2max = 0.694.ACSM + 3.33; R2 = 0.833, SEE = 4.4 ml.min-1.kg-1 (N = 40). The equations were cross-validated with 20 patients. The correlation between predicted and observed values was r = 0.98 and 0.97 without and with handrail support, respectively. The mean absolute prediction error (3.1 and 4.1 ml.min-1.kg-1) were similar to protocol-specific equations. We conclude that VO2max can be predicted independent of treadmill protocol with approximately the same error as protocol-specific equations.

The effect of limited handrail support on total treadmill time and the prediction of VO2 max

Holding onto the front handrail during treadmill testing significantly increases total treadmill time (TT) and predicted VO2max when compared with tests without front handrail support. By limiting the amount of handrail support to the tips of two fingers of one hand, the difference in TT can be substantially reduced. In the present study, the difference in TT between tests with and without handrail support for healthy men was not significantly different. However, this was not true for healthy women and for male patients with coronary artery disease and myocardial infarction.

Exercise testing without interruption of medication for refining the selection of mildly symptomatic patients for prognostic coronary angiography

OBJECTIVE

To examine how exercise testing on background medical treatment affects the ability of the test to predict prognostically important patterns of coronary anatomy in patients with a high clinical probability of coronary artery disease but who are well controlled on medication.

DESIGN

Prospective study.

SETTING

Regional cardiothoracic centre and referring district general hospital.

PATIENTS

84 patients with a history of typical angina or definite myocardial infarction and mild symptoms who had been placed on the waiting list for prognostic angiography.

INTERVENTION

Maximal exercise electrocardiography and radionuclide ventriculography performed off and on medication, followed by angiography within three months.

MAIN OUTCOME MEASURE

Prognostically important coronary artery disease for which early surgery might be recommended purely on prognostic grounds, irrespective of symptoms.

RESULTS

Coronary artery disease was present in 71/84 (85%) patients; in 28/84 (33%) patients this was prognostically important. When the result was strongly positive, the predictive accuracy for prognostically important disease was 0.46 off and 0.62 on medication for the exercise electrocardiogram and 0.71 off and 0.82 on medication for exercise radionuclide ventriculography. The likelihood ratio was 1.00 off and 1.36 on medication for exercise electrocardiography and 2.54 off and 10.5 on medication for exercise radionuclide ventriculography. In stepwise logistic regression, the test identified as the strongest predictor of prognostically important disease was exercise radionuclide ventriculography on medication for which the improvement chi 2 was 28 (p < 0.0001). With the regression model, the probability of important disease is 92% if exercise radionuclide ventriculography on medication is at least strongly positive, compared with 16% if the result is normal or just positive.

CONCLUSION

In patients likely to have coronary disease, exercise testing should be performed without interruption of medication to optimise its ability to identify those with prognostically important disease, and to help to avoid unnecessary or premature angiography in those who are well controlled on medical treatment.

Incremental evaluation of exercise capacity as an independent predictor of coronary artery disease presence and extent

To determine the independent incremental value of exercise capacity (METS) concerning the presence and extent of coronary artery disease, we analyzed data from 800 patients with suspected coronary disease who underwent both exercise testing and coronary angiography. We performed logistic regression analysis of clinical and exercise test data with an incremental design to mimic the usual flow of data acquisition. Separate analyses were performed concerning coronary disease presence (> or = 1 vessel with a > or = 50% lesion) and extent (three-vessel/left main disease). Diagnostic accuracy was determined by calculating receiver operating characteristic (ROC) curve areas. When considered alone, METS was a significant predictor of both presence and extent of disease. Multivariate analysis revealed that METS was an independent predictor of disease extent but not presence. However, comparison of ROC curve areas failed to show any loss of accuracy when METS was removed from the coronary disease extent analysis. Despite the strong univariate relationship between exercise capacity and coronary disease presence and extent and the independence of exercise capacity as a predictor of coronary disease extent, the lack of an additional incremental accuracy attributed to its consideration virtually cancels its value as a diagnostic variable for assessing both coronary disease presence and extent.

Independent and incremental prognostic value of exercise single-photon emission computed tomographic (SPECT) thallium imaging in coronary artery disease

OBJECTIVES

The objective of this study was to examine the independent and incremental prognostic value of exercise single-photon emission computed tomographic (SPECT) thallium imaging in patients with angiographically defined coronary artery disease.

BACKGROUND

Previous studies showed the importance of exercise thallium-201 in risk stratification. However, most of these studies used planar imaging techniques.

METHODS

Follow-up data were obtained in 316 medically treated patients with coronary artery disease. Cox proportional hazards regression models were used to examine the independent and incremental prognostic values of clinical, exercise, thallium and cardiac catheterization data.

RESULTS

There were 35 events (cardiac death or nonfatal myocardial infarction) at a mean follow-up time of 28 months. Univariate analysis showed that gender (chi-square = 5.1), exercise work load (chi-square = 3.1), extent of coronary artery disease and left ventricular ejection fraction (chi-square = 14.8) and thallium variables (chi-square = 22.7) were prognostically important. The thallium data provided incremental prognostic value to catheterization data (chi-square = 33.7, p < 0.01). The extent of the perfusion abnormality was the single best predictor of prognosis (chi-square = 14). Patients with a large perfusion abnormality had a worse prognosis than that of patients with a mild or no abnormality (Mantel-Cox statistics = 10.6, p < 0.001).

CONCLUSIONS

In medically treated patients with coronary artery disease, exercise SPECT thallium imaging provides independent and incremental prognostic information even when catheterization data are available. The extent of the perfusion abnormality is the single most important prognostic predictor.

Nomogram based on metabolic equivalents and age for assessing aerobic exercise capacity in men

OBJECTIVES

The goal of this study was to create a nomogram, based on maximal exercise capacity (in metabolic equivalents [METs]) and age, for assessing a patient's ability to perform dynamic exercise to quantify the level of physical disability or relative capacity for physical activity.

BACKGROUND

Providing an estimation of exercise capacity relative to age is clinically useful. Such an estimate can be derived from measured or estimated maximal oxygen uptake (in METs) from treadmill exercise testing and age. It is an effective means of communicating to patients their cardiopulmonary status, encouraging improvement in exercise capacity and quantifying disability.

METHODS

Exercise test results of 1,388 male patients (mean age 57 years, range 21 to 89) free of apparent heart disease who were referred for exercise testing for clinical reasons were retrospectively reviewed. This referral group as well as subgroups of active (n = 346) and sedentary (n = 253) patients were analyzed to determine norms for age and for age by decades for exercise test responses, including METs, maximal heart rate and maximal systolic blood pressure. Regression equations were calculated from this information, and a nomogram for calculating degree of exercise capacity from age and MET level achieved by a patient was created. A similar analysis was performed in a separate group of 244 apparently healthy, normal male volunteers (mean age 45 +/- 14 years, range 18 to 72) who underwent exercise testing with direct measurement of expired gases.

RESULTS

Equations for predicted METs for age were derived for the entire clinical referral group (METs = 18.0-0.15[Age]) and for the subgroups of active (METs = 18.7-0.15[Age]) and sedentary (METs = 16.6-0.16[Age]) patients. All results achieved statistical significance, with p values < 0.001. In the volunteer group of normal men who performed exercise testing with ventilatory gas exchange, the decline in maximal heart rate and METs with age was not as steep as in the referral group. Although the normal group confirmed nomograms published previously among similar subjects, the equations derived from the patients differed from those previously reported; in contrast to previous studies using healthy volunteers, the equations and nomograms for the referral group are more appropriate for patients typically referred for testing in a hospital or office-based internal medicine practice.

CONCLUSIONS

Norms for METs based on age are presented as well as population-specific nomograms that enable physicians to assess patients' exercise capacity relative to their age group.

Nonsustained ventricular tachycardia: identification and management of high-risk patients

NSVT is common in normal persons and in patients with a variety of heart diseases. When present in patients with coronary artery disease, particularly after a recent myocardial infarction, it is associated with an increased risk of sudden and nonsudden cardiac death. However, its prognostic significance in patients with nonischemic heart disease, with the possible exception of hypertrophic cardiomyopathy, remains controversial. In patients with coronary artery disease, certain diagnostic tools (e.g., determination of left ventricular function. PVS) help to identify low- and high-risk patients who may or may not benefit from antiarrhythmic treatment. There is no consensus at this point as to the best approach for identifying and treating high-risk patients. Ongoing clinical trials should provide important information on the roles of signal-averaged ECGs and PVS in the management of patients with NSVT and coronary artery disease. In the meantime, treatment should be individualized for each patient. beta-Blockers should probably be the first line of therapy to control symptoms. Asymptomatic potentially high-risk patients (i.e., those with LVEF < 40%) should be referred for enrollment in randomized controlled studies.

Development and validation of a logistic regression-derived algorithm for estimating the incremental probability of coronary artery disease before and after exercise testing

OBJECTIVES

Our goals were to develop and validate a multivariate algorithm for estimating the incremental probability of the presence of coronary artery disease.

BACKGROUND

Multivariate methods, including logistic regression analysis, have been extensively applied to diagnostic exercise testing. However, few previous studies have included both an incremental design and external validation.

METHODS

A retrospective collection of clinical, exercise test and catheterization data was performed involving four U.S. referral medical centers. All patients had no prior history of coronary disease and had undergone coronary angiography < or = 3 months after exercise stress testing. An algorithm was developed in one center (590 patients with a 41% prevalence of coronary artery disease) with the use of logistic regression analysis and was validated in the other three centers (1,234 patients, 70% prevalence). The algorithm incorporated pretest variables (age, gender, symptoms, diabetes, cholesterol), exercise electrocardiographic (ECG) variables (mm of ST segment depression, ST slope, peak heart rate, metabolic equivalents [METs], exercise angina) and one thallium variable. Discrimination was measured with receiver operating characteristic curve analysis. Calibration (that is, reliability) was assessed from a comparison of probability estimates and the actual prevalence of disease.

RESULTS

The overall incremental receiver operating characteristic curve areas for the validation group were pretest, -0.738 +/- 0.016; postexercise ECG, 0.78 (SE 0.017); and postthallium, 0.82 (SE 0.016); p < 0.01 for both increments. Within the three validation institutions, the institution with a disease prevalence closest to that of the derivation institution had the best incremental receiver operating characteristic curve areas. There was a stepwise incremental improvement in calibration especially from exercise ECG to thallium testing.

CONCLUSIONS

An incremental multivariate algorithm derived in one center reliably estimated disease probability in patients from three other centers. The incremental value of testing was best demonstrated when the derivation and validation groups had a similar disease prevalence. This algorithm may be useful in decision making that relates to the diagnosis of coronary disease.