Exercise radionuclide ventriculography in evaluating successful transluminal coronary angioplasty

The role of noninvasive cardiac imaging in the evaluation of the postcoronary intervention patient

Noninvasive diagnostic techniques are playing an increasingly prominent role in the evaluation of the postcoronary interventional patient. Radionuclide myocardial perfusion imaging has proved to be of value in assessing procedural success in patients with suboptimal angiographic results and/or multivessel coronary artery disease. However, in asymptomatic patients with single vessel disease, the use of myocardial perfusion imaging may not be cost-effective for follow-up after successful coronary intervention. The timing of these studies is important when used to predict coronary restenosis. Radionuclide ventriculography and echocardiography are two imaging modalities that, in conjunction with exercise stress, can be used to predict patient outcome and clinical events postcoronary intervention. A high degree of operator expertise is required for the optimal interpretation of the echocardiographic studies.

Coronary restenosis: what have we learned from angiography?

Coronary restenosis remains a major problem for interventional cardiology not only by virtue of its frequency, but also because of the current inability to prevent it. Symptomatic status and non-invasive evaluation have been used to study restenosis, but both lack specificity and sensitivity, particularly in patients with multivessel disease. Angiography remains the reference standard. Several arbitrary definitions have been used, some related to visual estimates of coronary stenosis and others to quantitative angiographic techniques. In another approach, linear modeling is used to assess minimal luminal diameter of lesions on restudy. Although angiographic studies have been essential in the study of restenosis, questions concerning the underlying mechanism and pathophysiology remain. The development of animal models that closely resemble human restenosis should allow evaluation of pathophysiologic mechanisms and development of new strategies to prevent the problem.

Restenosis after coronary angioplasty: an overview

Despite substantial basic and clinical efforts to address the problem of restenosis after percutaneous coronary intervention, effective preventive therapies have not yet been developed. Nevertheless, the accumulated information has provided much insight into the process of restenosis in addition to allowing standards to be developed for adequate clinical trials. The pathophysiology of restenosis increasingly appears to be distinct from that of primary atherosclerosis. Restenosis involves elastic recoil, incorporation of thrombus into the lesion and fibrocellular proliferation in varying degrees in different patients. Lack of an animal model that satisfactorily mimics restenosis is a major impediment to further understanding of the process. Clinical studies are hampered by difficulties in finding a single unifying definition of restenosis and by variable methods of reporting follow-up. Reporting of clinical outcomes of all patients in angiographic substudies would allow a more satisfactory interpretation of the results of clinical trials. Current noninvasive test results are not accurate enough to substitute for angiographic and clinical outcome data in intervention trials. In the majority of observational studies, only diabetes and unstable angina have emerged as consistently associated with restenosis; whereas most of the standard risk factors for atherosclerosis have a less consistent relation. Disappointingly, the new atherectomy and laser technologies have not affected restenosis rates. The one possible exception is coronary stenting, as a result of the larger luminal diameter achieved by the placement of the stent. In conclusion, although substantial continued effort is necessary to explore the basic aspects of cellular proliferation and mechanical alteration of atherosclerotic vessels, attention to the principles of clinical trials and observation are required to detect the impact of risk factors and interventions on the multifactorial problem of restenosis. Adequate sample sizes, collection of clinical and angiographic outcomes and factorial study designs hold promise for unraveling this important limitation of percutaneous intervention.

Radionuclide methods to evaluate percutaneous transluminal coronary angioplasty

Radionuclide angiocardiography and myocardial perfusion imaging with exercise are valuable methods to assess patients undergoing percutaneous transluminal coronary angioplasty. Successful angioplasty results in improvement in ventricular systolic and diastolic function and regional perfusion. Complications of angioplasty, such as periprocedural infarction and side branch occlusion, can be documented noninvasively. Radionuclide methods have also been demonstrated to be of prognostic value in predicting coronary artery restenosis and recurrent cardiac symptoms. However, to avoid underestimating the success of coronary revascularization, studies must be scheduled long enough following angioplasty to allow transient abnormalities associated with artery dilation to resolve.

Prognostic significance of silent myocardial ischemia detected by early treadmill exercise after coronary angioplasty

Three hundred ninety patients who had successful coronary angioplasty were studied by treadmill exercise testing to determine the incidence and prognostic importance of silent and symptomatic myocardial ischemia in this patient subset. All patients were followed for an average of 11 months. During exercise, 81 patients (20%) had abnormal exercise-induced ST-segment depression without chest pain (group 1). Twenty patients (5%) had chest pain without ST changes (group 2). Twenty-one patients (5%) had both exercise-induced chest pain and ST-T-segment depression (group 3) and 268 patients (70%) had a normal exercise test with no chest pain (group 4). The groups were similar with respect to age, sex, history of previous myocardial infarct and previous coronary bypass surgery. Group 4 included more patients with complete revascularization. Mutually exclusive cardiac events were defined as cardiac death, nonfatal myocardial infarction, class III angina and additional revascularization (coronary angioplasty, coronary artery bypass surgery). The cardiac event rate in groups 1, 2 and 3 were significantly higher than in group 4 (40, 45 and 43 vs 22%; p = 0.001). There were 4 cardiac deaths and 4 nonfatal myocardial infarctions in group 1 compared to 2 cardiac deaths and 3 nonfatal myocardial infarctions in group 4 (p = 0.03 and 0.05, respectively). The event rates in groups 1, 2 and 3 patients with multivessel disease were significantly greater than in group 4 (44, 60 and 47 vs 22%; p = 0.002). Thus, exercise-induced myocardial ischemic episodes, both symptomatic and silent, early after coronary angioplasty are predictive of an unfavorable prognosis and serious cardiac events, particularly in patients with multivessel disease and incomplete revascularization.

Prognostic value of early exercise stress testing after successful coronary angioplasty: importance of the degree of revascularization

The prognostic value of early exercise testing after successful coronary angioplasty was determined in 196 and 225 consecutive patients with single-vessel and multivessel coronary disease, respectively, who underwent a symptom-limited exercise test within 30 days of the procedure. The incidence of exercise-induced ST segment depression greater than or equal to 1 mm was significantly greater in patients with multivessel versus single-vessel disease (27% versus 14%; p less than 0.005) and in patients with multivessel coronary disease who had incomplete versus complete revascularization (36% versus 10%; p less than 0.001). An abnormal exercise ECG result was associated with a significantly increased risk of cardiac events in patients with multivessel disease but not in patients with single-vessel disease. Exercise-induced angina occurred in a small and similar proportion of patients with single and multivessel coronary disease (8% versus 12%). The presence of exercise-induced angina was associated with a higher incidence of follow-up cardiac events in patients with multivessel disease and incomplete revascularization (52% versus 33%; p less than 0.05). Exercise duration was significantly less in patients with multivessel disease who had a subsequent cardiac event compared with that in patients who did not have such an event (458 +/- 168 versus 519 +/- 156 seconds; p = 0.01). Thus an abnormal exercise ECG finding within 1 month of successful coronary angioplasty is predictive of subsequent cardiac events in patients who have multivessel disease. The prognostic content of the test might be further improved if the test were performed several months after the procedure when the risk of restenosis is greatest.

Quantitative analysis of thallium-201 uptake and washout before and after transluminal coronary angioplasty

Transluminal coronary angioplasty has become an important therapeutic modality in the treatment of coronary artery disease. The effects of coronary angioplasty on regional myocardial perfusion have been reported in only a small series of patients, employing subjective analysis of thallium-201 perfusion scintigrams. Thus, we studied 61 patients with quantitative analysis of thallium-201 uptake and washout before and after undergoing angioplasty. Prior to angioplasty, there were 105 areas in 47 patients with abnormal thallium-201 uptake during exercise, with a mean uptake of 49 +/- 1.3%. The uptake of thallium-201 in these same areas increased to 71.3 +/- 1.9% post angioplasty (P less than 0.0001), and 68 (65%) of the areas showing abnormal uptake returned to normal. Abnormalities in washout of thallium-201 before angioplasty were seen more frequently than in uptake (150 vs 105 areas, P less than 0.05), with 8 patients having abnormal washout in the presence of totally normal uptake. Thallium-201 washout in the abnormal areas improved from 16 +/- 2.8 pre angioplasty to -23 +/- 1.8% post angioplasty (P less than 0.001). Normalization resulted in 6 of the 8 patients with exclusively washout abnormality. Residual abnormalities in uptake and/or washout were seen in 53% of the patients, usually in areas with prior myocardial infarction or supplied by a vessel with significant stenosis which did not undergo angioplasty. Improved thallium-201 uptake and washout corresponded to reductions in percent coronary area stenosis (89 +/- 1.0 to 36 +/- 2.0%, P less than 0.001) and transstenotic pressure gradient (42 +/- 3.0 to 9.0 +/- 2.0 mm Hg, P less than 0.001). Thus, quantitative analysis of thallium-201 uptake and washout provided objective evidence for improved myocardial perfusion after coronary angioplasty. Due to a fairly high prevalence of residual perfusion abnormalities after this procedure, optimal assessment of benefits requires quantitative comparison of thallium uptake and washout before and after coronary angioplasty.

Restenosis after transluminal coronary angioplasty detected with exercise-gated radionuclide ventriculography

Forty-one patients were evaluated with exercise-gated radionuclide ventriculography before and within 4 days after successful transluminal coronary angioplasty and 4 to 12 months later. Patients were subgrouped according to the degree of restenosis demonstrated angiographically at 4 to 12 months (Group I [n = 23]: less than or equal to 20%; Group II [n = 10]: greater than 20% but less than 50%; Group III [n = 8]: greater than or equal to 50%). Patients with abnormal findings on gated radionuclide ventriculography (less than 5 point increase in ejection fraction or wall motion deterioration) early after angioplasty were eventually found to have a greater degree of restenosis than were patients with normal findings (41.2 +/- 30.3 versus 19.0 +/- 25.4% restenosis, p less than 0.0001). The accuracy of abnormal radionuclide ventriculography in predicting 50% or greater restenosis was 73% immediately after angioplasty and 77% at the time of follow-up angiography. Gated radionuclide ventriculographic results were abnormal in 5% of Group I patients compared with 75% of Group III patients (p less than 0.01) early after angioplasty; at late follow-up, they were abnormal in 27% of Group I patients compared with 88% of Group III patients (p less than 0.01). Group I patients had a greater increase in ejection fraction than did Group III patients at early (+11.3 +/- 7.5 versus + 3.5 +/- 6.5 points, p less than 0.01) and late (+11.8 +/- 7.8 versus -1.9 +/- 8.7 points, p less than 0.0005) follow-up. It is concluded that gated radionuclide ventriculography is useful in predicting coronary restenosis after transluminal coronary angioplasty.

Exercise, electrocardiographic and functional responses after percutaneous transluminal coronary angioplasty

Exercise testing after successful PTCA showed improved cardiac functional status on examination of electrocardiographic and symptomatic responses, myocardial perfusion and global and regional left ventricular function. Sixty-six patients were studied before and after persistently successful PTCA. Follow-up studies an average of 8 months after the successful procedure showed an incidence of abnormal testing of only 7% using both electrocardiographic and subjective symptomatic criteria during treadmill studies and no abnormal studies with thallium scintigraphy. Radionuclide cineangiography demonstrated similar left ventricular ejection fractions at rest before and after PTCA, but an improvement of 9 +/- 10% (p less than 0.001) in the exercise ejection fraction at follow-up. However, 52% of patients with paired data still had an abnormal radionuclide cineangiographic study after successful PTCA, raising the question of the presence of subclinical ischemia or a false-positive result.