Exercise technetium 99m sestamibi single-photon emission computed tomography late after coronary artery bypass surgery: long-term follow-up

Prognostic value of stress imaging after revascularization: a systematic review of stress echocardiography and stress nuclear imaging

BACKGROUND

Risk assessment may be important in patients being considered for repeat revascularization after prior coronary intervention or surgery. We sought the prognostic value of radionuclide stress myocardial perfusion imaging or echocardiography among patients with previous revascularization.

METHODS

Studies on the outcomes of stress imaging tests after revascularization were selected from an electronic search if they reported the odds or hazard ratio (HR) of an abnormal stress test in the prediction of mortality (cardiac or total), hard cardiac events (cardiac death and myocardial infarction [MI]), total hard events (total mortality and MI]), or overall events (cardiac death, MI, and repeat revascularization).

RESULTS

In 29 studies (12,874 patients, 63 ± 3 years, 80% men), an abnormal test result was associated with hard cardiac events (HR 1.2, 95% CI 1.1-1.3), cardiac mortality (HR 5.8, 95% CI 0.8-10.8), total mortality (HR 2.2, 95% CI 1.3-3.1), total hard events(HR 2.4, 95% CI 1.4-3.3), and overall events (HR 1.2, 95% CI 1.1-1.3). The nature of the end point was not associated with differences in the prediction of events, but the type of revascularization showed a significant association with outcome, with percutaneous intervention portending a worse outcome. Age and the timing of the stress imaging postrevascularization were inversely associated with survival. Gender, length of follow-up after testing, symptom status, past infarction, and risk factor status did not explain interstudy heterogeneity.

CONCLUSIONS

In patients with previous revascularization, abnormal results at stress echocardiography or radionuclide myocardial perfusion imaging are predictive of subsequent events, with age, type of revascularization, and the timing of the stress imaging after revascularization being important sources of heterogeneity between studies.

Myocardial perfusion scintigraphy: the evidence

This review summarises the evidence for the role of myocardial perfusion scintigraphy (MPS) in patients with known or suspected coronary artery disease. It is the product of a consensus conference organised by the British Cardiac Society, the British Nuclear Cardiology Society and the British Nuclear Medicine Society and is endorsed by the Royal College of Physicians of London and the Royal College of Radiologists. It was used to inform the UK National Institute of Clinical Excellence in their appraisal of MPS in patients with chest pain and myocardial infarction. MPS is a well-established, non-invasive imaging technique with a large body of evidence to support its effectiveness in the diagnosis and management of angina and myocardial infarction. It is more accurate than the exercise ECG in detecting myocardial ischaemia and it is the single most powerful technique for predicting future coronary events. The high diagnostic accuracy of MPS allows reliable risk stratification and guides the selection of patients for further interventions, such as revascularisation. This in turn allows more appropriate utilisation of resources, with the potential for both improved clinical outcomes and greater cost-effectiveness. Evidence from modelling and observational studies supports the enhanced cost-effectiveness associated with MPS use. In patients presenting with stable or acute chest pain, strategies of investigation involving MPS are more cost-effective than those not using the technique. MPS also has particular advantages over alternative techniques in the management of a number of patient subgroups, including women, the elderly and those with diabetes, and its use will have a favourable impact on cost-effectiveness in these groups. MPS is already an integral part of many clinical guidelines for the investigation and management of angina and myocardial infarction. However, the technique is underutilised in the UK, as judged by the inappropriately long waiting times and by comparison with the numbers of revascularisations and coronary angiograms performed. Furthermore, MPS activity levels in this country fall far short of those in comparable European countries, with about half as many scans being undertaken per year. Currently, the number of MPS studies performed annually in the UK is 1,200/million population/year. We estimate the real need to be 4,000/million/year. The current average waiting time is 20 weeks and we recommend that clinically appropriate upper limits of waiting time are 6 weeks for routine studies and 1 week for urgent studies.

Long-term prognosis after a normal exercise stress Tc-99m sestamibi SPECT study

BACKGROUND

Patients with a normal stress technetium 99m sestamibi study were shown to have a favorable outcome at intermediate-term follow-up. However, long-term survival has not been studied. The aim of this study was to evaluate the incidence and predictors of mortality and cardiac events at long-term follow-up after a normal exercise stress sestamibi study. Methods and results We studied 218 patients (mean age, 53 +/- 10 years, 108 men) who had normal myocardial perfusion assessed by Tc-99m sestamibi single photon emission computed tomography at rest and during symptom-limited bicycle exercise stress test. Endpoints during a follow-up period of 7.4 +/- 1.8 years were hard cardiac events (cardiac death and nonfatal myocardial infarction) and all-cause mortality. During follow-up, 13 patients died of various causes (cardiac death in 1 patient). Ten patients had nonfatal myocardial infarction (a total of 11 hard cardiac events). By multivariate analysis, independent predictors of cardiac events were history of coronary artery disease (chi(2) = 5, P =.03) and lower exercise heart rate (chi(2) = 12, P =.001). Independent predictors of all-cause mortality were age (chi(2) = 4, P =.05) and exercise heart rate (chi(2) = 5, P =.03). The annual mortality rate was 0.6% in the first 5 years and 1.8% between the sixth and eighth years. The annual hard cardiac event rate was 0.7% in the first 5 years and 1.5% between the sixth and eighth years. Receiver operating characteristic curves identified an exercise heart rate lower than 130 beats/min as the cutoff value that separated patients with regard to their risk for mortality and hard cardiac events.

CONCLUSIONS

It is concluded that the annual mortality and cardiac event rate is less than 1% during 5-year follow-up after a normal exercise sestamibi study. Therefore repeated testing would not be required unless there is a change in symptoms. Follow-up should be closer in patients with a history of coronary artery disease and in those who fail to achieve an exercise heart rate of 130 beats/min or greater.

Long-term outcome of a residual scar from myocardial infarction after coronary artery bypass grafting: a 100-month study using myocardial perfusion scintigraphy

The prognosis for patients with a residual scar from myocardial infarction (MI) after coronary artery bypass grafting surgery (CABG) has not been fully evaluated, so the present study retrospectively evaluated such patients with stress myocardial single photon emission computed tomography (SPECT) at 100 months after CABG. The study group consisted of 24 subjects (23 males, 1 female; mean age, 59+/-9 years) in whom CABG had been performed more than 100 months (mean follow-up period 135+/-25 months) previously. The 24 subjects were classified into 3 groups according to their summed stress score (SSS) and summed reversibility score (SRS) in the early period after CABG. Eight subjects with MI (SSS> or =2 and SRS<2) were classified into the group MI, 8 subjects with ischemic myocardium (SSS> or =2 and SRS> or =2) was classified into the group RE, and 8 subjects with normal perfusion (SSS<2 and SRS<2) was classified into group N. None of the subjects in group MI required revascularization. Cardiac events occurred in 4 of the group RE patients and all required revascularization. As to the SPECT scoring system, the long-term SSS of group MI (6.4+/-3.1) was not different from that in the early periods (4.3+/-4.0; NS). However, the long-term SSS values of group RE (8.8+/-6.2) were significantly greater than those soon after CABG (3.4+/-1.8; p=0.03). In group N, there was also no difference in the SSS values between the early period (0.3+/-0.5) and the long-term period (0.0+/-0.0; NS). Patients with a residual scar from MI in the early period after CABG did not worsen over a period of 100 months. Moreover, there was no significant difference in the SPECT score in the segment with the residual scar in the short or long term after CABG. However, the extent of reversibility was directly associated with the presence of clinical events. Therefore scintigraphic imaging remains an important and clinically relevant risk stratification tool. Stress myocardial SPECT, early after CABG, can be used to predict the possibility of future cardiac events or the need for revascularization.

Technetium-99m labeled myocardial perfusion imaging agents

99mTc labeled myocardial perfusion tracers have significantly advanced the field of noninvasive diagnostic evaluation and risk stratification of patients with known or suspected coronary artery disease by providing comprehensive information about myocardial perfusion and function from a single study. Of various currently available invasive and noninvasive test modalities, myocardial perfusion imaging provides the most powerful prognostic information that is incremental to the information obtained from invasive evaluation. Future research should focus on the development of perfusion tracers that linearly track myocardial blood flow over a wide range and have minimal splanchnic uptake. Availability of an effective attenuation and scatter correction program would further eliminate some of the current limitations of this technique.

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.