Preliminary evaluation of coronary artery disease begins with a medical history and physical examination. Blood tests, electrocardiogram or echocardiogram and stress test are usual next steps. The following diagnostic tests are used for those patients who do not obtain a conclusive diagnosis after preliminary tests.15
Angiography is the current gold standard for diagnosing coronary artery disease.1 It remains the standard because no other currently available test can define as accurately the extent of coronary luminal obstruction.13 The level of risk for diagnostic angiography is very low; however, coronary angiography does have limitations. First, there is a significant variation rate associated with the interpretation of angiograph films. Studies show interpretations differ not only in whether or not disease is present but also in the severity of the stenosis present. Erroneous interpretation of angiograph films can have serious consequences: some patients will be under-treated and others over-treated. Studies have shown this variation rate to be directly related to 8% of PTCA and CABG procedures being performed inappropriately.1 As one respondent remarked "I might refer one patient for PTCA a week while another cardiologist assessing the same cases might refer four PTCAs." Suggestions to reduce variation focus on the diagnostic physician consulting with at least one other physician; the best approach would be a case discussion involving fellow cardiologists, interventionalist, and surgeons. These consultations provide an interdisciplinary approach aimed at assisting the diagnostic physician in the interpretation of films and arriving at an appropriate course of action.2 Such "cath conferences" used to be the standard of practice (in New Jersey and elsewhere) - however, due in part to the increasing isolation of interventional cardiologists and the popularity of "ad hoc" angioplasty, they are no longer common. Where "cath conferences" are still common, such as at Kaiser Permanente (KP) Southern California, it is claimed that they improve appropriate utilization of cardiac services. KP Southern California still convenes daily case conferences where treatment plans for all but the most routine cases are discussed by internists, cardiologists and cardiac surgeons together.
The second limitation of coronary angiography is attributable to our inability to accurately define the etiology of the obstruction or detect the presence of non-obstructive atherosclerotic disease.13 In fact, the procedure has the potential to miss up to 70% of disease indicators because it cannot scan artery walls for so-called vulnerable plaques.2 Cardiologists have learned that up to two-thirds of acute myocardial infarctions are caused by blockages that fill less than half of an artery's lumen which result from the rupture of small plaques. These plaques are known as vulnerable plaques because they have soft, fatty centers, which are easily ruptured. When ruptured these plaques become clots, which can quickly obstruct blood flow to the heart causing an AMI. Therefore, it is essential for cardiologists to understand not only the size of gradually forming obstructions but also the consistency of plaques, which can cause an immediate life threatening obstruction.2 This problem may be addressed by adjunctive procedures such as coronary intravascular ultrasound, which has the potential to permit assessment of vulnerable plaques. Coronary intravascular ultrasound is used to make luminal measurements, characterize atheroma size and plaque distribution, and assess the composition of lesions.13 Each of these elements is important in the emerging understanding of plaque behavior.
Guidelines on Back-up Surgery for Coronary Angiography
The ACC/AHA guidelines on surgical back-up for coronary angiography, first published in December of 1993 but unchanged in guidelines updated in May 1999, state that "many (diagnostic) catheterization laboratories are located in hospitals without on-site cardiac surgery facilities. Although there is no evidence that outcomes are worse in these laboratories, if "ad hoc" angioplasty is anticipated, or the patient is likely to need urgent or emergent surgery after angiography, transfer to a hospital that can provide both diagnostic and therapeutic procedures should be strongly considered."13
Coronary Magnetic Resonance Imaging (MRI)
Coronary MRI is a non-invasive procedure that uses a high-powered magnetic field to provide images of the heart including chambers and arteries. It can take detailed images of blockages and walls, identify "vulnerable plaques," and measure blood flow.2
Coronary MRI is currently still investigative, but expected by some experts to develop into possibly the principal diagnostic tool for CAD over the next half-dozen years if it can produce a direct, high-quality image of the coronary artery.28 There are strong differences of opinion on the potential of coronary MRI to displace angiography but if this occurs, coronary MRI could revolutionize the diagnosis of CAD for five reasons. First, unlike other imaging tools, MRI can evaluate in a single test heart function, perfusion, and viability - information a cardiologist currently obtains through a series of tests. Second, MRI is able to accurately view the walls of arteries and differentiate between those so-called dangerous "vulnerable plaques" and more stable plaques.2 Third, MRI is non-invasive, and thus might be preferred by patients. Fourth, communication and computer technology can combine with coronary MRI to make it possible to read these images anywhere in the world; all patients in New Jersey could have their images read in a centralized location (anywhere in the world), with advantages in terms of decreased variability in interpretation. Fifth, MRI is a tool of radiologists, and its use would introduce a new group of specialists into the decision-making process for patients with CAD.
Echocardiography is a technique that sends sound waves into the chest to rebound from the heart's walls and valves. The recorded waves show the shape, texture and movement of the valves on an echocardiogram.2 Additionally, echocardiograms show the size of the heart chambers and how well they are working. Echocardiography can be conducted while the patient is at rest or under a stress-induced state with the use of treadmills or pharmaceuticals. The echocardiogram is established as a means for assessing cardiac valve function. ACC/AHA guidelines currently state, however, "most patients undergoing a diagnostic evaluation for angina do not need an echocardiogram."19 Among our respondents there were mixed feelings about the current state of echocardiography: some respondents stated that there probably is an excess of echocardiograms currently being performed by cardiologists, but others emphasized the importance of the technology and the quality of the images it produces.
Coronary angiography, despite its limitations, remains the principal clinical tool in the assessment of coronary artery disease and will likely remain so in the near future.13 Adjunctive tools such as intravascular ultrasound complement coronary angiography, resulting in more conclusive information. The demand for coronary angioplasty may be superficially heightened by bias in the interpretation of angiography films. The issue of self-referral and the potential for inappropriate use of angioplasty was raised by the majority of our respondents. Group consultations have been recommended as a way to reduce variation and improve the appropriateness of cardiac service utilization. Coronary magnetic resonance imaging has the potential to complement or even substitute for coronary angiography. This technology could revolutionize the delivery of care but is currently experimental. There are varying opinions on the role of echocardiography.
ACUTE MYOCARDIAL INFARCTION (AMI)
"Cardiology experts agree that unless specific contraindications are present, every patient who has experienced symptoms of ischemia for at least 30 minutes and who presents within 12 hours of symptom onset should be considered for PTCA or thrombolysis and evaluated to determine if they meet the criteria for such therapy."5
Preferred Therapy: Thrombolytics and/or PTCA
The ACC/AHA recently issued updated guidelines suggesting that PTCA ('primary angioplasty") be considered as an alternative to thrombolytics "if performed in a timely fashion (balloon inflation within 90 minutes of admission) by individuals skilled in the procedure (more than 75 procedures per year) and supported by experienced personnel in a laboratory environment (centers performing more than 200 angioplasty procedures per year that have cardiac surgical capabilities)."7 New Jersey respondents felt that as long as door-to-balloon time is under one hour PTCA is better than thrombolytics; however it is not unusual for "door-to-balloon" time to hover close to two hours. The peer reviewed clinical literature favors PTCA slightly over thrombolytics for patients presenting with AMI because it achieves earlier restoration of blood flow.5 Earlier restoration of blood flow results in improved short-term outcomes, i.e. reduced rates of death, reinfarction, recurrent ischemia, and stroke.5, 7 Conversely, early restoration is key to the use of thrombolytics also: if thrombolytics could be administered faster, they might be favored over PTCA because of the risk that always accompanies an invasive procedure. Some feel that, given PTCA's current advantages, it is presently underutilized. These respondents indicated that in the future, angioplasty might supplant much of thrombolytic therapy. Another future variant might be combination therapy. This approach uses thrombolytic therapy to open the infarct-related artery rapidly thus providing a safer and more complete reperfusion by PTCA later. Preliminary results from the Plasminogen Activator Angioplasty Compatibility Trial (PACT) suggest that combination therapy can be superior to the use of either modality alone.7 This is an area in which the science is changing very rapidly, however.
Long-term Outcome Limitations
Although studies have shown angioplasty provides a short-term clinical advantage over thrombolytic therapy, this may not be sustained in the long run.14 Angioplasty is associated with a 10-15% risk of recurrent ischemia and reocclusion of the related vessel,4, 6 and at six month follow-up evaluations the rates increase to 40% for restenosis and reocclusion of the related artery.4, 19 Other research, such as the Myocardial Infarction Triage and Intervention investigation, cited no difference in outcomes during a three year follow-up for acute myocardial infarction patients treated with PTCA and thrombolytic therapy.7 Compared with surgery, PTCA has resulted in the need for additional revascularization procedures. Reoccurrence of AMI and mortality showed little difference when comparing PTCA and CABG.24
The Evolving Role of Intercoronary Stents
About 70-90% of PTCA procedures also involve the placement of a stent.15 Studies report that the benefit of stents outweighs the benefit of PTCA alone in patients with AMI.3 Compared with PTCA, stent deployment in patients with AMI was associated with a significantly lower frequency of in hospital acute occlusion and significantly less need for revascularization in the 6 months following AMI.4, 7, 24 Some respondents stated that the use of stents without surgical back up will become commonplace. The safety of using stents in AMI patients with a visible thrombus has been controversial. Traditionally, use of stents in these cases was considered extremely dangerous. But today, with the complement of high-pressure implantation techniques and post stent anticoagulation the risk is low (1.3%). Heparin coated stents enhance the safety and effectiveness of stent deployment in conjunction with PTCA for AMI patients.6
At the November, 2000 meeting of the American Heart Association further advances in the development of both PTCA and thrombolytic therapy were discussed. It seems likely that, over the next five years, consensus on the best practices for treatment of AMI patients is likely to change more than once. This makes it extraordinarily challenging to frame an appropriate state regulatory policy. Currently, in most situations, optimal thrombolytic therapy should still be regarded as an excellent reperfusion strategy10 with hemorrhage being the most significant risk to patients.5
The Importance of Time and Transportation in Treating AMI with Primary PTCA
Research findings indicate that death rates nearly double as door to balloon time increases from less than 1 hour to longer than 3 hours for primary PTCA.9, 18
Several approaches have been advanced to overcome these time limitations for patients who have considerable travel time to a hospital providing PTCA. One option is pre-hospital thrombolytic therapy, which is provided at the site where the patient is initially encountered (i.e. patient's home). Portable electrocardiograph devices and easy-to-use thrombolytic agents make pre-hospital therapy a viable option for those patients who are at high risk of dying in the ambulance en route to the facility.8 A third option is further developing transportation infrastructure to more effectively accommodate those patients in more isolated areas.
Guidelines for Back-up Surgery for Primary Angioplasty/Stenting
The ACC/AHA have issued a joint statement about backup surgery indicating that there may be patients "at very high risk suffering myocardial infarction, who may or may not be suitable for thrombolytic therapy, in whom emergency angioplasty without on-site surgical back up is acceptable treatment if the ability to transfer the patient to an established angioplasty center on a timely basis is not possible or attendant with additional risks."14 Surgery is necessary in less than 1% of the cases where an AMI patient is first treated with PTCA, and some cardiologists today feel that, if in-house surgical capability is not available, an effective transfer system can be adequate in case of PTCA emergent complications.7 However, at this time such circumstances are expected to be the exception rather than the rule, with transport to a cardiac surgery center for performance of primary angioplasty remaining the norm - indeed, ACC/AHA guidelines state that "In point of fact, surgical backup has become a surrogate for experienced, well-equipped laboratories."14 The ACC/AHA guidelines specify stringent criteria for laboratories which perform primary angioplasty, and the ACC/AHA Task Force Committee in its report states that it "…feels compelled to underscore its conviction that angioplasty/surgical centers constitute the best venue for all angioplasty procedures."14 In addition to these clinical considerations, it would not be cost-effective for a hospital without on-site cardiac surgery to develop PTCA capacity for a relatively low volume of primary PTCA cases.
Treatment for Chronic Stable Angina
Risk Factor Management and Pharmacological Treatment
Risk factor management focuses on areas such as smoking cessation, weight loss where indicated, exercise programs, control of high blood pressure, lowering cholesterol levels and managing diabetes. Pharmacological therapy focused on the prevention of acute myocardial infarction has developed considerably in recent years.19 Research developments indicate that the use of aggressive lipid-lowering therapy is at least as effective as angioplasty in reducing the incidence of ischemic events.16 Additional pharmacological therapies that have long been established for use, but are currently being underused, include aspirin and a variety of anti-anginal agents (i.e. Beta blockers).19
Increased effectiveness of risk factor management has been achieved through the use of anti-hypertensive drugs, beta blockers and cholesterol-reducing agents and aspirin. Patients have become more accepting of these therapies in order to avoid the dramatic acute episodes of illness. With evidence of genetic components to CAD, interest has turned to risk factor assessment as well as modification. Ultimately, the development of coronary MRI as a valid and reproducible tool for imaging coronary arteries might mean easier CAD patient identification and earlier and more effective risk modification strategies.
Catheter-Based and Surgical Revascularization Procedures
Percutaneous transluminal coronary angioplasty and coronary artery bypass grafting are currently the two well-established options for increasing myocardial blood supply in patients with chronic stable angina.19 Professional respondents remarked that there is a clear trend towards substituting catheter based therapies for surgery. This may be attributed to the introduction of stents since angioplasty has been established for some time. Angioplasty with stent deployment is less likely to result in recurrent stenosis (obstruction) during the first six months after the procedure. This is in part responsible for the increase in angioplasty volumes, but at the same time that increase is viewed by some respondents as a cause for concern. As one respondent put it, with the increasing popularity of angioplasty among cardiologists as the treatment of choice, the de facto guidelines for performing PTCA are widening "to the left and to the right," making potentially inappropriate procedure decisions (the choice of angioplasty over surgery for a patient with multiple-vessel disease, for example) less apparent.
"Ad Hoc" PTCA
Nationally, respondents have reported that there has been an increase in coronary diagnostic and interventional procedures being completed at the same time, although data on this trend are generally not available (and were not available to the authors of this report). There is wide variation in the use of this "ad hoc" strategy. Many respondents feel that "ad hoc" PTCA has resulted in more angioplasty being performed than is necessary. Studies have shown that there is no difference "in the need for emergent CABG, CABG at any time during hospitalization, death at any time during hospitalization or MI" even after adjusting for case mix when comparing these outcomes for "ad hoc" PTCA patients versus patients for whom PTCA was performed separately from angiography.11 Some facilities may endorse the "ad hoc" strategy to reduce costs (although studies have shown an inconsistent cost savings with PTCA without the use of stents)17 and appease patient preference unless there is a specific reason not to do so. Others support a more conservative approach of reviewing diagnostic studies before proceeding to intervention. The federal Health Care Financing Administration (HCFA) has no specific Medicare policy for reimbursing "ad hoc" PTCA. The overriding principle is that providers may not bill separately for a combined procedure, but there is no audit to determine whether physicians engage in "double billing." Also, there is no one day or three day rule to delineate between the procedures. As long as the angioplasty and angiogram are performed on two separate visits it is permissible to bill for each.
Guidelines for Back-up Surgery for Elective Angioplasty
ACC/AHA 1993 guidelines mandate backup surgery for all elective angioplasty procedures.14 As respondents pointed out, there is infrequent need to utilize back up surgery for angioplasty but "there are no low risk patients - the risk for complication requiring surgical back up is real if you are that 1%."
Radiation therapy is a promising procedure which has recently received preliminary indication of probable approval by the FDA. It prevents the development of scar tissue that may form after the implantation of a coronary stent. The therapy involves threading a catheter into the affected coronary artery and exposing the affected segment to radiation. Initially, radiation therapy was thought to hold great promise but now it is widely held that it's need will be negated by specially treated coronary stents that prevent scarring themselves.29