Cardiac catheterization does not directly benefit patient outcome, and its value as a diagnostic test derives from the detailed structural and functional information it provides that allows the clinician to assess prognosis accurately and to select the most appropriate long-term management strategy. Therefore, indications to use this procedure are interwoven with indications for possible therapeutic plans such as PTCA or CABG.
Patients come to cardiac catheterization for several indications that may develop at any time during the initial hospitalization for unstable angina. Cardiac catheterization is usually indicated in patients who fail to stabilize with medical therapy or have break-through symptoms despite adequate medical therapy and high-risk patients categorized by other clinical findings or noninvasive testing. Other possible indications for catheterization include significant CHF, malignant ventricular arrhythmias, significant LV dysfunction or large perfusion defect by noninvasive study, or physical examination, or echocardiographic evidence of significant MR, aortic stenosis, or hypertrophic cardiomyopathy. Finally, patients in an intermediate- or high-risk category with previous PTCA or CABG should generally be considered for cardiac catheterization, unless prior catheterization data indicate that no further revascularization is likely to be technically possible (Figure 12).
In all cases, the general indications for catheterization and revascularization are tempered by individual patient characteristics and preferences. In the very frail elderly and in those with serious comorbid conditions, patient and physician judgments about risks and benefits are particularly important.
The purpose of cardiac catheterization is to provide detailed data about the size and distribution of coronary vessels, the location and extent of atherosclerotic disease in the coronary arteries, the extent of focal and global LV dysfunction, and the presence and severity of coexisting cardiac disorders (such as valvular or congenital lesions).
Revascularization refers to a set of procedures (both percutaneous and surgical) that have as their principal goal restoration, to the extent possible, of normal arterial blood flow to the myocardium. Although general guidelines can be offered, the decision to refer a patient for a revascularization procedure and the selection of the appropriate procedure both require the exercise of clinical judgment and thorough counseling with the patient and his or her family regarding the expected risks and benefits.
This guideline proposes two alternative definitive treatment strategies termed "early invasive" and "early conservative." Randomized trial data did not support the inherent superiority of either strategy based on medical outcomes (TIMI IIIB, in press). The decision about which strategy to pursue for a given patient should be based on the patient's estimated risk (Chapter 1), available facilities, and patient preference. These strategies are defined below.
Recommendation: In the early invasive strategy, cardiac catheterization is performed routinely in all hospitalized patients without contraindications, usually within 48 hours of presentation (strength of evidence = A). Recommendation: In the early conservative strategy, cardiac catheterization is performed routinely in patients admitted to the hospital with unstable angina who are candidates for a revascularization procedure and have one or more of the following high-risk indicators: prior revascularization (PTCA or CABG); associated CHF or depressed LV function (EF <0.50) by noninvasive study; malignant ventricular arrhythmia; persistent or recurrent pain/ischemia; and/or a functional study indicating high risk (strength of evidence = A). Recommendation: Diagnostic catheterization should not be performed on patients with extensive comorbidity in whom the likely benefits of revascularization in terms of length and quality of life would not outweigh the risks (strength of evidence = B).The proper role and timing of cardiac catheterization in unstable angina remains controversial. Diagnostic catheterization benefits patients primarily by enhancing the accuracy of prognostic stratification which can be used to adjust medical therapy as well as to plan specific revascularization therapy. The population of patients with unstable angina admitted to the hospital includes a subgroup that should routinely receive catheterization and another subgroup for whom invasive study is optional and can be deferred pending further clinical developments. The group that should routinely receive catheterization consists of all high-risk patients (see Table 8) and intermediate-risk patients with a prior PTCA or CABG, patients with CHF or depressed resting LV function (i.e., EF <0.50) by noninvasive study, and patients recognized to be high risk by noninvasive exercise or pharmacologic stress testing. Decisions about catheterization in the low- or moderate-risk patients who also have a low-risk functional test can be individualized based on the practice setting (i.e., availability of invasive diagnostic and therapeutic procedures) and the patient's preferences.
The principal data upon which these recommendations are based are the TIMI IIIB (in press) results. This study randomized 1,473 patients with unstable angina requiring hospital admission to early (18-48 hours) invasive or early conservative strategies. At 42 days, 15.5 percent of the early invasive patients had died, had a nonfatal MI, or had a positive 6-week exercise test versus 17.7 percent of the early conservative patients (p=0.26). Ninety-seven percent of the invasive group underwent diagnostic catheterization (as assigned) compared with 64 percent of the conservative group (p < 0.001). Revascularization by 42 days had been performed in 61 percent of the invasive group and 49 percent of the conservative group (p <0.001). In addition, conservatively treated patients had a significantly higher use of antianginal medications and more hospital readmissions by the 6-week followup.
Although data are not available to permit a formal cost-effectiveness analysis of these alternate strategies, any savings realized initially in the group not receiving cardiac catheterization appear to be largely offset by the need for longer hospitalization initially and for subsequent care. Unless continued followup of these patients shows late survival benefit for patients treated by the early invasive strategy, the aggressiveness of early use of cardiac catheterization and revascularization procedures would appear to be best determined by the preferences of the individual patient with unstable angina.
Patients who present with intermediate- or high-risk unstable angina and a history of a prior PTCA within the past year have a high incidence of restenosis which often can be effectively treated by repeat angioplasty. Noninvasive testing is not sufficiently accurate to detect restenosis in these patients, and coronary angiography without preceding functional testing is generally indicated. Patients with prior CABG surgery and intermediate- or high-risk unstable angina represent a second group for whom a strategy of early coronary angiography is generally indicated. In patients with recent bypass, early graft stenosis frequently can be treated with angioplasty. The complex interplay between progression of native coronary disease, development of graft atherosclerosis with ulceration and embolization, and the potential for noncardiac chest pain all argue for a greater need to visualize coronary arteries by catheterization in patients with prior bypass surgery than in patients with similar presenting symptoms but no prior procedure.
Patients with CAD and known or suspected poor LV function, such as patients with known prior Q-wave MIs or those who have had prior measurements of LV function or who present with CHF, have sufficient probability of benefit from revascularization procedures to merit direct coronary angiography without preceding functional testing.
Confirmation of normalcy in patients presenting frequently with symptoms of unstable angina and no objective evidence of ischemia represents another valid indication for cardiac catheterization. Identification and management of this patient group is described more fully in Chapter 3.
In unstable angina, results of catheterization typically show the following profile: (1) normal coronary arteries or insignificant CAD in 10 to 20 percent, (2) significant (i.e., >50%) left main disease in 5 to 10 percent, (3) three-vessel disease in 20 to 25 percent, (4) two-vessel disease in 25 to 30 percent, and (5) single-vessel disease in 30 to 35 percent. In the TIMI IIIB (in press) early invasive strategy, no significant CAD >60 percent obstruction was found in 19 percent of patients, one-vessel disease in 38 percent, two-vessel disease in 29 percent, three-vessel disease in 15 percent, and left main disease (>50 percent obstruction) in 4 percent. Lesions are often eccentric with irregular borders in patients with unstable angina, and irregular lesion morphology has correlated with an increased risk of ischemia, MI, and cardiac death ( Bugiardini, Pozzati, Borghi et al., 1991).
Discovery that a patient does not have significant obstructive CAD can help avert improper "labeling" and prompt a search for the true cause of symptoms. High-risk patients with two-vessel disease including patients with severe proximal LAD involvement, and those with severe three-vessel or left main disease should be considered for CABG. Many other patients will have less severe lesions that do not put them at high risk of cardiac death but can have a substantial negative impact on their quality of life. As compared with high-risk patients, low-risk patients will receive negligible or very modestly increased chances of long-term survival with CABG. Therefore, quality of life and patient preferences will be given more weight than strict clinical outcomes in selecting a treatment strategy. Low-risk patients whose symptoms do not respond well to maximal medical therapy and who experience a significant negative impact on their quality of life and functional status may be considered for revascularization. Patients in this group who are unwilling to accept the increased short-term procedural risks to gain long-term benefits or who are quite satisfied with their existing capabilities should be managed medically at first and followed carefully as outpatients. Other patients willing to accept the risks of revascularization and wishing to improve their functional status or to decrease symptoms may be considered appropriate candidates to undergo early elective revascularization.
It is not possible presently to define an arbitrary extent of comorbidity that would in every case make referral for cardiac catheterization and further invasive procedures inappropriate. As a general principle, the potential benefits of catheterization and revascularization must be carefully weighed against the risks which may be significantly greater in patients with significant comorbidity. This decision is further complicated because even when CABG surgery is not an option, high-risk patients may benefit from a palliative PTCA or other interventional procedure.
The case of the high-risk patient with significant comorbidities calls for especially thoughtful discussion between the health care practitioner, patient, and family. The decision for or against revascularization should be made on a case-by-case basis, and all parties should be in mutual agreement. Patients and families should understand that the presence of significant comorbidities can alter the revascularization risk-to-benefit ratio and negatively influence patient outcomes.
Examples of extensive comorbidity within the spirit of this recommendation include:
More difficult decisions involve patients with significant comorbidity but not as significant as described above. Examples of this group of patients include those with:
The nature of the facility performing the catheterization also can be an important consideration in this evaluation. Specifically, the availability of interventional cardiologists experienced in high-risk and palliative PTCA should be considered, as should the availability of an experienced cardiac surgeon able and willing to take on complex, high-risk cases.
Revascularization is used to improve prognosis, relieve symptoms, and improve functional capacity in patients with obstructive CAD. In general, the indications for revascularization in the unstable angina patient who has been stabilized are the same as for stable angina, but the impetus for some form of revascularization is stronger than in stable angina. Moreover, long-term survival rates after CABG are similar for unstable angina patients who present with rest angina, increasing angina, new onset angina, or post-MI angina (Rahimtoola, Nunley, Grunkemeier et al., 1983).
CABG and PTCA are the two revascularization strategies available, and implicit in this guideline is the understanding that the initial treatment selection will be modified or supplemented when necessitated by changes in the patient's condition. Thus, subsequent referrals of a PTCA patient to CABG surgery or of a CABG surgery patient to PTCA (i.e., therapeutic crossovers) are integral parts of the initial treatment strategy. However, excessive crossover rates suggest inappropriate treatment selection, inadequate technical results, or both. Furthermore, although the percutaneous intervention strategy is referred to in this guideline as "PTCA," it should be recognized that this term refers to a family of techniques including standard balloon angioplasty, perfusion balloon (prolonged dilatation) angioplasty, atherectomy, laser angioplasty, and intracoronary stenting. Thus, once the decision has been made to attempt percutaneous coronary revascularization, a further decision is required about the optimal mode(s) of such intervention.
The TIMI-IIIB (in press) results comparing early invasive versus early conservative catheterization and revascularization have been described in the cardiac catheterization section of this chapter. Two randomized trials compared medical and surgical therapy in unstable angina. The National Cooperative Study Group randomized 288 patients between 1972 and 1976 at nine academic centers ( Russell, Moraski, Kouchoukos, 1978). The Veterans Administration Cooperative Study randomized 468 patients between 1976 and 1982 at 12 VA hospitals ( Luchi, Scott, and Deupree, 1987; Parisi, Khuri, Deupree et al., 1989; Scott, Luchi, and Deupree, 1988; Sharma, Deupree, Khuri et al., 1991). Both studies included patients with progressive or rest angina accompanied by ST- and T-wave changes. Patients over age 70 or with a recent MI were excluded. The VA study included only men.
In the National Cooperative Study, hospital mortality was 3 percent for medicine and 5 percent for CABG surgery (p=NS). Followup to 30 months failed to show any differences in survival between the therapies. In the VA study, survival to 2 years was the same for medicine and CABG surgery overall and in subgroups defined by number of diseased vessels. A post-hoc analysis of patients with depressed LV function, however, showed a significant survival advantage with CABG surgery. All randomized trials of CABG surgery versus medicine (including those in stable angina) have found improved symptom relief and functional capacity with CABG surgery. Long-term followup in these trials has suggested that by 10 years there is a significant attenuation of both symptom relief and survival benefits from CABG surgery. However, these randomized trials reflect an earlier technical era for both CABG surgery and medicine. Improvements in anesthesia and surgical techniques, including internal mammary artery grafting to the LAD artery and improved intraoperative myocardial protection with cold potassium cardioplegia, are not reflected in these trials. Also, the routine use of heparin and ASA in the acute phase and the range of therapeutic agents available represent significant differences in current practice from the era in which these trials were performed.
Three published and two unpublished randomized trials of PTCA have now been reported, but only one of these, the Randomized Intervention Treatment of Angina (RITA), enrolled unstable angina patients. The VA Angioplasty Compared with Medicine (ACME) trial tested PTCA versus medicine in single-vessel disease and found improved functional status and quality of life at 6 months in the PTCA arm ( Parisi, Folland, Hartigan et al., 1992). The RITA trial enrolled 1,011 patients in the United Kingdom with one-, two-, or three-vessel disease that had equal chance of revascularization success with either PTCA or CABG ( RITA, 1993). Approximately 60 percent of the enrolled patients were reported to have angina at rest prior to randomization. An interim analysis at 2.5 years of followup has shown equivalent hard cardiac events (death, MI) and a much higher repeat revascularization rate in the PTCA arm. The German Angioplasty Bypass Surgery Investigation (GABI), which randomized 358 patients with multivessel CAD and > class II angina to CABG or multivessel PTCA, recently reported that at 6-month followup, the primary endpoint (angina rates) was similar, and there was no significant difference in the rates of hard cardiac events (death, MI) between the CABG and PTCA groups. Initial results have recently been presented for the Coronary Artery Bypass Revascularization Investigation (CABRI) trial involving 1,054 multivessel CAD patients randomized to PTCA or CABG. The Emory Angioplasty vs. Surgery Trial (EAST) also reported, but has not published, outcomes in 392 patients with multivessel disease, including a majority of patients with unstable angina, randomized between PTCA and CABG. The reported results of these two unpublished trials do not differ substantially from the reported results of the RITA trial.
One large registry compared 5-year survival with medicine, PTCA, and CABG in 9,263 CAD patients with unstable angina (defined as symptoms requiring hospital admission for control and to rule out MI) treated between 1984 and 1990 ( Mark, Nelson, Califf et al., in press). In this nonrandomized comparison, extensive statistical adjustments were used to control for prognostically important baseline differences created by treatment selection. For patients with three-vessel disease or two-vessel disease with a proximal severe (>e;95%) LAD artery stenosis, surgical survival at 5 years was significantly better than medicine, and a similar trend in favor of CABG was found in comparison with PTCA. In less severe two-vessel CAD, revascularization improved survival relative to medicine, and there was a trend for PTCA to provide better survival results (due to lower procedural mortality) than CABG. In one-vessel disease, all therapies were associated with high 5-year survival rates with very small differences among groups.
The available data can be used to formulate some general principles about the proper role of revascularization in acute IHD. The first general principle is the more extensive the CAD, the larger the benefit in survival realized from revascularization ( Califf, Harrell, Lee et al., 1989). In the most severe forms of CAD (e.g., left main disease, three-vessel disease), CABG provides the best long-term survival results. In intermediate forms of CAD (e.g., two-vessel disease), revascularization provides improved survival relative to medicine, although the absolute survival benefit is smaller than in three-vessel disease. In general, the patient with high-risk two-vessel disease (as defined by impaired LV function, older age, or coexisting vascular disease) will have improved survival with CABG surgery as compared with other patients who have two-vessel disease and similar anatomy. For other two-vessel disease patients, PTCA may provide modest survival benefits relative to medicine. In the least severe CAD patients (i.e., one-vessel disease), observational data have shown good survival associated with medical therapy, PTCA, and CABG. The primary treatment choice is usually between medicine and PTCA, with CABG reserved for those patients with large areas of myocardium at risk, those who fail medical therapy, or those who are technically unsuitable for PTCA.
The second general principle is that survival benefits of revascularization are magnified on the absolute scale by factors that increase overall medical risk, especially LV dysfunction and advanced age. In particular, multivessel CAD benefits from CABG are substantially larger on an absolute scale in patients with depressed LV function. These factors tend to increase the procedural risks of revascularization somewhat but offer proportionally greater long-term benefits than can be expected with medical treatment ( Califf, Harrell, Lee et al., 1989; McCormick, Schick, McCabe et al., 1985).
The decision between angioplasty, bypass surgery, or medical treatment is a difficult one for many patients. Many patients fear death or disability from surgery more than from the progression of their disease. Other patients view bypass surgery as a panacea for their condition that will allow them to avoid difficult changes in their present lifestyle, even though a repeat procedure may be needed later. All care providers, especially physicians directly responsible for care during procedures, should provide a balanced and accurate summary of risks and benefits of all reasonable therapeutic options.
Patient expectations regarding the benefits of revascularization are quite variable. In one study, bypass patients were asked before their surgery about the benefits they expected to obtain ( Gortner, Gilliss, Paul et al., 1989). Six months later, they were resurveyed to determine which benefits had been achieved. Women realized fewer expected benefits than men (62% vs. 90%, p <0.05). In addition, younger patients realized fewer expected benefits than older patients. Often the patients held unrealistic expectations. Assessment of expectations before a procedure may help a patient and physician make a more appropriate treatment decision.
The following information should be recorded in the medical record:
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