Selecting PCI, CABG or medical therapy: Current Recommendations
- General description of procedure, equipment, technique
- Indications and patient selection
- Details of how the procedure is performed
- Interpretation of results
- Outcomes (applies only to therapeutic procedures)
- Alternative and/or additional procedures to consider
- Complications and their management
What’s the evidence?
General description of procedure, equipment, technique
1.) Optimal medical therapy (OMT)
OMT encompasses the spectrum of medications (and exercise) that reduces morbidity and mortality of the coronary artery disease (CAD) process. In comparison with revascularization, the focus is often on medications that are prescribed to reduce the burden of angina, primarily by allowing vasodilation and a reduction of the cardiac workload (pressure x rate product).
The conventional therapies that accomplish this goal include nitrates, calcium channel blockers, and beta blockers. A number of newer agents have emerged, which can be used even in combination with the conventional therapies. However, the only non-conventional drug approved by the FDA in the USA for the treatment of angina is ranolazine, which works through inhibition of the late inward sodium channel, thereby reducing the intracellular calcium concentration. Nicorandil is approved for angina treatment in Europe and Asia and mediates potassium channel opening and nitrate effects. Ivabradine is a specific inhibitor of the pacemaker current of the sinus node and exerts its anti-anginal effect by heart rate reduction.
Other approaches overlap with optimal treatment of the cardiovascular risk factor profile and improve cardiovascular health, especially endothelial health. These other approaches include high-dose statin therapy, angiotensin-converting enzyme (ACE) or angiotensin receptor blocker (ARB) type I receptor inhibition, and even allopurinol. Antiplatelet therapy with either aspirin or clopidogrel is also standard practice.
2a.) Percutaneous coronary intervention (PCI)
PCI entails the elimination of the flow-limiting aspect of a coronary artery stenosis by catheter-mediated plaque compression and stabilization with metallic scaffolds. Standard devices include balloons of different size and compliance and stents without or with a particular polymer coating and drug release capacity (so-called bare metal and drug-eluting stents). Other devices that are less frequently used include cutting balloons and rotablators. The choice of device depends on the anatomic/lesion needs.
2b.) Coronary artery bypass grafting (CABG)
CABG accomplishes the "bypassing" of a coronary artery stenosis with a conduit vessel from the aorta or its adjunct vessels, i.e., the internal mammary artery. This procedure is performed either as open heart surgery with sternotomy or as a minimally invasive direct coronary artery bypass (MIDCAB) surgery with limited anterior thoracotomy and the use of endoscopic or robotic techniques. Both of these types of surgeries can be performed with or without the use of a cardiopulmonary bypass pump.
"Hybrid procedures" entail the combination of MIDCAB surgery and PCI, especially MIDCAP left internal mammary artery (LIMA) to left anterior descending (LAD) coronary artery grafting combined with PCI of the left circumflex artery (LCX) and/or right coronary artery (RCA) lesions.
Indications and patient selection
All patients with CAD are to receive OMT as detailed above. This serves two purposes: 1) reduction of progression of the atherosclerotic disease process and "stabilization" of coronary artery plaques and cardiac function, thereby reducing the occurrence of major adverse events, and 2) improvement of symptoms and quality of life. Obviously, this is the only therapy for patients who explicitly express the wish not to pursue invasive therapies.
Revascularization strategies are to be pursued if the two goals stated above cannot be accomplished by medical therapy alone, i.e., for prognostic or symptomatic indications, in the absence of contraindications. In the setting of acute coronary syndrome, both indications are usually met and PCI is most often the preferred strategy.
Under no other circumstance is the indication for revascularization stronger than in the setting of acute heart failure complicating acute myocardial infarction, particularly cardiogenic shock, in which case revascularization should be as complete as possible.
Other clear indications for revascularization for prognostic implications include left main stenosis >50%, any proximal LAD stenosis >50%, 2- or 3-vessel disease with impaired LV function, or single remaining patent vessel with >50% stenosis PLUS documented fractional flow reserve (FFR) <0.80 or documented ischemia.
In particular, if non-invasive testing demonstrates a large burden of ischemia (formally >10% of LV or informally more than 3 segments on echo or nuclear stress testing), revascularization is considered.
For symptom control, revascularization is indicated for any stenosis >50% with limiting angina or angina equivalent unresponsive to OMT.
Selecting the best revascularization strategy depends on a number of factors. One of the currently best tools available for an informed decision is the SYNTAX score. Especially in patients with complex coronary artery disease (CAD), the decision should be reached utilizing a Heart Team approach, which includes the valued opinion of an interventional cardiologist and a cardiovascular surgeon. The Heart Team may define the preferred revascularization strategy for any given patient. However, often both procedures can be performed and the decision will be that of the patient and his/her advocate physician in the context of the overall clinical presentation.
PCI is usually the preferred option for 1- or 2-vessel disease not involving the proximal LAD.
PCI reaches near equivalence with CABG for 1- or 2-vessel disease involving the proximal LAD, isolated ostial or shaft left main disease, and 3-vessel disease with simple lesions and technical feasibility of complete revascularization. All of these circumstances can be summarized in a SYNTAX score of <23.
PCI can be pursued but tends to be inferior to CABG for a distal left main (bifurcation) lesion, especially in combination with 2- or 3-vessel disease and a SYNTAX score of <32.
CABG is the preferred option for left main disease with 2- and 3-vessel disease and a SYNTAX score >32.
CABG is also the preferred option even in the presence of a lower SYNTAX score when multiple complex lesions are present and PCI remains technically limited to achieve complete revascularization. CABG is also preferred in diabetic patients with multivessel disease.
Other than prompted by a decision for comfort care, there is no contraindication to continue with any of the medical therapies outlined.
Either PCI or CABG is not to be pursued if a competent patient or power of attorney refuses informed consent or expresses irrevocable DNR/DNI orders.
Otherwise, an invasive strategy is not recommended in the presence of an unfavorable risk-benefit ratio. This entails a very low-risk clinical presentation and severe comorbidities limiting life expectation regardless of cardiac intervention, under which circumstance the risk of the procedure is higher than any meaningful clinical benefit. In particular, revascularization is not recommended in the absence of (limiting) symptoms with OMT or 1-vessel disease without proximal LAD involvement and <10% ischemic burden. Likewise, an invasive strategy may be of extraordinarily high risk despite a perceived benefit, e.g., PCI for extremely complex CAD without surgical back-up.
Even primary PCI should not be performed in hospitals without on-site cardiac surgery capabilities and a proven rapid transfer plan for emergency CABG at a near-by facility, including implementation of appropriate modes of hemodynamic support.
Details of how the procedure is performed
This procedure is performed by interventional cardiologists in conjunction with a team of trained nurses and technicians in a catheterization laboratory.
Following appropriate selection and review of the indications and contraindications, informed consent is obtained (written unless the patient has an ST segment elevation myocardial infarction (STEMI) or is in cardiogenic shock, in which case orally witnessed consent or family consent suffices to avoid delays).
Most medications are continued for the procedure with a few important specifications. Metformin is to be discontinued as early as possible before the procedure, especially with renal dysfunction (which may require additional hydration). On the other hand, anti-platelet therapy is a requirement and is not to be discontinued. In fact, dual anti-platelet therapy should be in place for PCI under the circumstance of acute coronary syndrome. Most often, aspirin (325 mg) is given and, as the clinical situation dictates, either clopidogrel (300 mg at least 6 hours prior or 600 mg at least 2-3 hours prior) or another thienopyridine such as prasugrel or ticagrelor or glycoprotein IIb/IIIa inhibitors.
Heparin infusion is discontinued before the start of the procedure, and most commonly still, unfractionated heparin will be used to achieve an activated clotting time of 250-300 seconds. This mode of anticoagulation starts after vascular access is obtained (radial or femoral artery, rarely brachial artery) and has to be in place before device entry into the coronary artery. Alternatively, bivalirudin may be used.
A series of angiographic images defines the lesion severity and anatomy, which determines the interventional approach. On occasion, additional modalities are used to aid in the procedural planning such as intervascular ultrasound. Depending on these evaluations, either direct implantation of a stent at the lesion is pursued or balloon angioplasty or rotational atherectomy followed by stent implantation. All of these devices are advanced via a guiding catheter, placed at the coronary artery origin, and a guidewire, which extends from the outside of the guiding catheter to the coronary vasculature beyond the lesion site.
Following the procedure, imaging techniques are used to confirm the outcome and all equipment is removed with the exception of the vascular access sheath, which will be removed once deemed safe by the abating anticoagulation status. All patients are monitored for several hours following the procedure.
Patients at low risk of complications and close proximity to medical facilities can be dismissed with close follow-up including next-day visit. Otherwise, patients are monitored on a dedicated unit with next-day dismissal in the absence of complications.
This procedure is performed by a specialized cardiovascular surgery team which includes not only the surgical staff but also anesthesiologists, nurses, technicians, and perfusionists. CABG is performed in an operating room embedded in a hospital structure.
Following review of indications, contraindications, risks, benefits, and alternatives, informed consent is obtained by the team. Often the patient also visits with the anesthesiologist in preparation for surgery. Aspirin is usually acceptable; however, for most surgeons, clopidogrel and most certainly GPIIb/IIIa inhibitors are not acceptable as they lead to an unacceptably high bleeding risk. For the same reason, heparin is to be discontinued prior to the procedure.
Other medications are often continued. In particular, beta blocker therapy should be continued, also to reduce the incidence of peri-operative atrial fibrillation. In patients with contraindications to beta blocker therapy and who are at high risk (previous atrial fibrillation and mitral valve surgery), amiodarone is recommended (600 mg PO per day for one week before surgery and 200 mg per day until discharge thereafter; otherwise, 400 mg PO BID x 7 days or 1 gr IV per day x 2 days after surgery).
The procedure starts with intubation and induction of general anesthesia, followed by a median sternotomy. Next, the internal mammary artery(ies) are mobilized or radial artery or saphenous bypass grafts are harvested. Subsequently, the pericardial sac is opened and the heart is exposed. In order to allow safe grafting of the bypasses on arteries with minimal luminal diameters in the mm range, a "still-stand" must be induced either by embedding the heart in a cardioplegic solution after connecting the patient to an extracorporeal circulation via a cardiopulmonary bypass pump or by device fixation with an "off-pump" approach. Cross-clamping of the aorta allows construction of the proximal anastomoses.
Once these preparatory measures are in place, the mobilized internal mammary artery end or one end of the graft conduit is sewn onto the coronary arteries distal to the stenoses. In cases of radial artery or saphenous venous grafts, the other end is sewn onto ostia generated in the ascending aorta. The latter can be performed even with a partially occluded aorta and with a beating heart. Blood flow is gradually allowed in order to monitor for any possible leak. Functional bypass graft status is then tested by used of a Doppler probe following vasodilator (papaverine) administration. Once everything is found satisfactory, all devices are removed and closure is pursued, including sternal wiring.
Subsequently, the patient is transferred to the intensive care unit for post-operative care including extubation and monitoring of hemodynamic stabilization. Often even the following day, the patient is transferred to the stepdown unit and dismissed home four days later with cardiac rehabilitation in place.
Interpretation of results
Patients on OMT require regular follow-up and need to be instructed to seek medical contact with any change in symptoms. Routine stress testing of these patients is not recommended. Hence, the clinical presentation is the interpretation of the success of OMT.
Similar to OMT, the clinical course defines the result of the revascularization procedure. Obviously beforehand, one would like to establish the goals and benefits of a procedure; the results of the procedure should meet these goals.
Outcomes (applies only to therapeutic procedures)
As outlined above, all patients are to receive OMT. In the absence of strong indications, revascularization does not change prognostic and/or symptomatic outcome.
The suitability of the approach of primary OMT was highlighted in the COURAGE trial, which, however, entailed coronary angiography to define a certain subset of patients who would not be better served with revascularization. Over a follow-up period of 5 years, patients without unstable angina, significant left main disease, markedly abnormal stress test, ejection fraction (EF) <30% and PCI-unsuitable lesions, sustained death or non-fatal MI as often with OMT alone as with OMT+PCI upfront (nearly 20% of patients), and were hospitalized for acute coronary syndrome just as often (approximately 12%). However, if not combined with PCI at the time of angiography, patients managed with OMT alone faced an absolute 10% higher risk of undergoing future revascularization procedures and experiencing angina within the first year.
These data are in full agreement with the atherosclerotic disease process itself in that lesions that cause fatal and non-fatal myocardial infarction often display outward remodeling and hence remain below the radar of symptoms and conventional modes of assessment. For this very reason, OMT remains key to influencing the overall outcome of CAD patients regardless of their presentation and assessment.
An important element in the interpretation of available data is the functional significance of coronary artery stenoses. This is often not accounted for in the calculations of the benefits of revascularization.
Whether symptomatic or not, a large burden of ischemia portends a poor prognosis, especially sudden cardiac death, which is averted by revascularization. The threshold of ischemic burden at which a mortality benefit with revascularization emerges is approximately 10%, and it is most definitely prominent at 20%. A heart with a reduced level of functioning may be even more susceptible to the negative implications of recurrent episodes of ischemia, especially extensive ischemia.
As it is usually complex CAD that underlies those presentations, most of these patients will undergo CABG even though some can be managed with PCI as outlined above. For this reason, the data in stable CAD, overall, are not as convincing for PCI as they are for CABG. This is different for patients with acute coronary syndrome, who are primarily managed with PCI. However, the same principles of risk-benefit stratification apply.
While data from different trials are not in agreement, the consensus is that patients with non-ST segment MI or unstable angina and a Thrombolysis in Myocardial Infarction (TIMI) risk score >2 derive a benefit from an invasive approach and revascularization. In this setting, revascularization yields a 20% relative reduction in death, MI, and rehospitalization over OMT. This benefit may not become apparent until after discharge. The benefit is at least twice as much and more immediate in the setting of an ST-segment myocardial infarction. Finally, the benefit is even more substantial in cardiogenic shock, in which revascularization leads to a 20% absolute mortality reduction.
Alternative and/or additional procedures to consider
Enhanced external counterpulsation (EECP)
This technique utilizes three pairs of cuffs around the lower extremities that are inflated to high pressure (300 mmHg) sequentially from distal to proximal during diastole, allowing retrograde aortic blood flow and augmentation of diastolic coronary perfusion. A number of other mechanisms have been discussed as well that might contribute to the clinical benefit observed, which includes reduction of angina burden in 70% of patients, with the elimination of nitroglycerin use in 50% of patients. This procedure is without any untoward effects and is covered by Medicare/Medicaid for patients with medically treated Canadian Cardiovascular Society (CCS) III/IV angina who are not candidates for revascularization therapies.
Spinal Cord Stimulation at Th1/Th2 level
This technique suppresses the activity of intrinsic cardiac neurons during myocardial ischemia and hence exerts primarily an analgesic effect. It is safe and effective in improving symptoms and quality of life for patients with refractory angina. Nevertheless, this technique is to be reserved for selected patients only.
Transmyocardial laser revascularization
This technique uses laser to generate transmural channels in the ischemic myocardium. It was thought that this would allow passive myocardial perfusion with oxygenated blood from inside the left ventricular (LV) cavity. However, within one day essentially all channels are closed and no objective proof for the original theory could be given. Other mechanisms such as sympathetic denervation and induction of angiogenesis have been discussed. Clinically, there is often a delay of benefit, if any, and the procedure has a mortality rate of 3%-5% (up to 12% reported). Hence, while FDA-approved, this strategy should be pursued only with extreme caution.
Complications and their management
Medical therapy always needs to be monitored for potential complications, i.e., side effects. Antiplatelet therapy increases the bleeding risk, and high-dose statin therapy can cause hepatocellular injury and myopathy, as well as–and most feared–rhabdomyolysis. ACE inhibitor therapy can lead to angioedema. These are examples of complications of medical therapy. For each individual patient, the profile and signs and symptoms of side effects must be discussed, and the patient must be alerted to seek medical attention with any concerns. Follow-up laboratory assessment such as the liver enzyme panel should be routine with statin therapy. Management of any of these complications is to stop the medication and to discuss alternative options.
What’s the evidence?
Fihn, SD, Gardin, JM, Abrams, J. "2012 ACCF/AHA/ACP/AATS/PCNA/SCAI/STS guideline for the diagnosis and management of patients with stable ischemic heart disease: a report of the American College of Cardiology Foundation/American Heart Association task force on practice guidelines, and the American College of Physicians, American Association for Thoracic Surgery, Preventive Cardiovascular Nurses Association, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons". Circulation . vol. 126. 2012 Dec 18. pp. e354-471.(Most current guideline review and guidance on the management of patients withCAD, including optimal medical therapy.)
Hillis, LD, Smith, PK, Anderson, JL. "2011 ACCF/AHA Guideline for Coronary Artery Bypass Graft Surgery A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Developed in collaboration with the American Association for Thoracic Surgery, Society of Cardiovascular Anesthesiologists, and Society of Thoracic Surgeons". J Am Coll Cardiol. vol. 58. 2011. pp. e123-210.(Reference publication on surgical revascularization of CAD.)
Levine, GN, Bates, ER, Blankenship, JC. "2011 ACCF/AHA/SCAI Guideline for Percutaneous Coronary Intervention. A report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions". J Am Coll Cardiol. vol. 58. 2011. pp. e44-122.(State-of-the-art reflection on catheter-based interventions for CAD.)
Wijns, W, Kolh, P, Danchin, N. "Guidelines on myocardial revascularization". Eur Heart J. vol. 31. 2010. pp. 2501-55.(An excellent companion on clinical merit of coronary revascularization procedures.)
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