Keith Dufendach, Dustin Kliner, and Ibrahim Sultan
Introduction
Heart disease is the leading cause of death for both men and women in the United States resulting in approximately 655,000 deaths per year. Ischemic heart disease (IHD) is the most common form of heart disease killing 365,914 patients in the year 2017 alone. Patients may present with a variety of symptoms ranging from stable angina or dyspnea on exertion to ST elevation myocardial infarction (STEMI) and cardiogenic shock. In addition to optimal medical therapy (OMT), many patients benefit from revascularization with either coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI). Familiarity with patient selection, technique, and potential complications of PCI is critical for the cardiac surgeon.
Noninvasive Testing for Ischemic Heart Disease
Testing for IHD should always begin with a thorough history and physical examination, usually performed by the patient’s primary care physician or cardiologist. For patients with chest pain or shortness of breath, non-cardiac causes should also be considered. Patients who present with acute angina should be classified with stable or unstable angina and may undergo a series of noninvasive tests based on pre-test probability of IHD.
- Resting electrocardiogram (EKG):
A resting EKG is recommended as an initial test in all patients with chest pain and without an obvious non-cardiac cause of their pain.
- Cardiac stress test:
An exercise stress test is recommended for all patients with intermediate or high pre-test probability of IHD who are able to participate in at least moderate exercise. An exercise stress test can be performed using EKG, echocardiography, or nuclear myocardial perfusion imaging. A pharmacologic stress test using either echocardiography, nuclear myocardial perfusion, or cardiac magnetic resonance imaging (cMRI) imaging is acceptable in patients who are unable to perform moderate exercise.
- Coronary commuted tomography angiography (CCTA):
CCTA is a rapidly improving technology for evaluation of coronary anatomy and is recommended in patients with an intermediate or high risk of CAD for whom cardiac stress testing is contraindicated. Some cardiologists even recommend CCTA as the first noninvasive test for coronary disease.
- Cardiac magnetic resonance imaging:
Cardiac MRI is not widely considered a standard modality for coronary evaluation but may be used in combination with pharmacologic stress testing for suspected IHD. This is particularly useful when performing cMRI for evaluation of another cardiac structure, such as the aortic valve.
Medical Management of the Patient with Ischemic Heart Disease
Medical therapy for patients with stable IHD should be provided according to the ACC/AHA guidelines and includes risk factor modification through lifestyle changes and pharmacologic therapy. Lifestyle changes include weight control, increased physical activity, alcohol moderation, smoking cessation, sodium reduction, and increased consumption of fresh fruits, vegetables, and low-fat dairy products. Pharmacologic therapy for patients with stable IHD includes antiplatelet therapy with either aspirin or another p2Y12 inhibitor such as clopidogrel or ticagrelor. Beta blockade is recommended in all patients with reduced ejection fraction (≤40%) or after MI or acute coronary syndrome (ACS). Beta blockers should be considered as chronic therapy for all other patients with IHD. Angiotensin converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARB) are recommended for all patients with stable IHD and either hypertension, diabetes mellitus (DM), left ventricular systolic dysfunction, or chronic kidney disease (CKD).
Percutaneous Coronary Intervention: Indications
The indications for PCI depend on the patient’s clinical presentation, symptoms, coronary anatomy, and functional assessment of coronary lesions. For patients with ACS, the presence of a STEMI mandates immediate assessment in the catheterization lab with the goal of rapid reperfusion of an acutely blocked coronary artery. In this case, PCI is the primary method of revascularization. CABG is reserved for patients for whom PCI cannot be performed, if the patient’s total burden of coronary disease warrants CABG and immediate surgery can be performed, or in the case of certain serious complications related to PCI such as coronary dissection or rupture. In the case of non-STEMI (NSTEMI), the patient should be admitted for serial cardiac enzyme assessment, usually with troponin I, anticoagulation with heparin, and coronary angiography. If the troponin levels do not stabilize, the patient experiences new or worsening chest pain, or the patient develops a STEMI, catheterization should be pursued immediately. Patients with unstable angina (UA) should also undergo coronary angiography, but this may be performed as an outpatient depending on symptom severity. In cases of NSTEMI and UA, complete revascularization of significant lesions with either PCI or CABG is recommended.
For patients with stable IHD who undergo coronary angiography, revascularization should be based on vessel anatomy, disease severity assessed with SYNTAX score, and functional assessment with fractional flow reserve (FFR) or instantaneous wave-free ratio (iFR). In 2007, the results of the COURAGE trial were published comparing OMT alone to OMT plus PCI in patients with stable CAD. The study demonstrated no difference in the primary outcome of death from any cause or nonfatal myocardial infarction (MI) over a median 4.6-year follow-up. These findings encouraged the continued development of drug-eluting stents (DES) and functional assessment with FFR or iFR. FFR and iFR involve the use of a specialized coronary pressure wire inserted beyond a coronary lesion to simultaneously assess the pressure differential between the aorta and coronary artery. FFR must be assessed after induction of maximal hyperemia, usually with the drug adenosine or regadenoson, and the cutoff for a significant lesion is 0.80, based on clinical trials. IFR does not require pharmacologic induction of hyperemia and is measured automatically during the “wave-free” period of diastole. The cutoff for a hemodynamically significant lesion using iFR is 0.89, with clinical results that are equivalent to using FFR. IFR has two advantages over FFR including the ability to assess serial lesions along a single coronary artery and reduced patient discomfort. Targeted revascularization based on FFR or iFR has resulted in improved clinical outcomes for those undergoing OMT plus PCI versus PCI alone, primarily driven by the decreased need for urgent revascularization. Thus, coronary lesions should be assessed with either FFR or iFR, and only those with a value less than or equal to 0.80 in FFR or 0.89 in iFR warrant coronary stenting.
The choice of revascularization strategy, either CABG or PCI, requires careful consideration and must include a detailed assessment of coronary anatomy and individual patient risk factors. In fact, according to ACC/AHA guidelines, a heart team approach including interventional cardiology and cardiac surgery is recommended for decision making with regard to revascularization strategy. This is particularly important in cases of unprotected left main coronary artery disease or complex multi-vessel disease involving the left anterior descending coronary artery.
Percutaneous Coronary Intervention: Technique
The technical aspects of coronary intervention are numerous, and a brief description of a routine PCI case is as follows. Once the patient is properly positioned supine on the table, central arterial access must be obtained. A 6 French sheath in the right radial artery is the preferred access strategy for patient comfort and reduction in risk of bleeding, though the femoral approach has similar outcomes with regard to major adverse cardiovascular events or mortality. Once access has been obtained, the patient is given a dose of systemic heparin and often an arterial vasodilator, such as nitroglycerin, verapamil, or nitroprusside. Following this, a standard 0.035” guidewire is advanced to the aortic root, and a catheter is advanced over the wire to position it within the ascending aorta. The wire is subsequently removed and the catheter is positioned in the coronary ostium. Radiopaque contrast is then injected into the coronary ostia and the images are recorded. Suspicious lesions with at least 50% narrowing of the left main or 70% narrowing of the remaining major epicardial arteries are then evaluated with either FFR or iFR, unless ischemia has been previously documented on outpatient noninvasive testing. This is performed using a 0.014” pressure wire that is advanced through the catheter and guided beyond the suspicious lesion under fluoroscopy. FFR or iFR is then calculated by simultaneous transduction of the pressure at the tip of the catheter and the end of the pressure wire either with (FFR) or without (iFR) adenosine administration. The cutoffs for FFR and iFR are 0.80 and 0.89, respectively, for a hemodynamically significant lesion.
Once the decision is made to proceed with PCI, the patient is usually given another dose of systemic heparin to prevent coronary thrombosis. The pressure wire is exchanged for a working 0.014” coronary wire which is advanced past the lesion. A balloon is then passed over the working wire and inflated in the area of stenosis. A drug eluting stent is then passed over the wire to the area of stenosis and the stent is deployed. Finally, a noncompliant balloon is expanded within the stent to ensure the stent is completely open. At this point, repeat angiography is performed to confirm successful stent deployment. Occasionally, intravascular ultrasound is used to ensure there are no areas of ongoing stenosis or kinking in the stented area, assess adequate expansion of the stent, and evaluate for the presence of coronary injury either proximal or distal to the freshly implanted stent. Once satisfied with the result, all wires and catheters are removed, and the activated clotting time is checked to ensure safe removal of the arterial sheath. The catheter is removed after a radial artery pressure device is applied (radial approach) or a percutaneous closure device is used (femoral approach). The patient is brought to the recovery area for post-procedure monitoring. The patient should be given a bolus dose of a P2Y12 receptor blocker (clopidogrel, prasugrel, or ticagrelor) in the recovery area. Dual antiplatelet therapy is usually continued for one year after stenting in the setting of acute coronary syndrome, or at least 6 months with a presentation of stable ischemic heart disease.
Alternative situations sometimes arise in the catheterization lab and include left main PCI, branch-vessel PCI, and chronic total occlusions. Various techniques are available to interventional cardiologists specializing in these complex cases. Cases involving any of these scenarios are high risk and should ideally be performed only at experienced centers after discussion with a heart team and with cardiac surgical backup.
Percutaneous Coronary Intervention: Complications
Complications relating to PCI are of particular interest to the cardiac surgeon and warrant further attention. Coronary perforation or dissection may occur as a result of coronary catheter or wire manipulation and warrant immediate transfer to the operating room for bypass of the area of coronary injury as well as any additional significant lesions which had been identified during coronary angiography. Post-infarct ventricular disruption, either septal or free wall defect, commonly occurs several days after AMI and represents another surgical emergency, which should be repaired promptly with cardiopulmonary bypass.
Additional non-surgical complications related to PCI include access site bleeding, periprocedural MI, spontaneous MI, cerebrovascular accidents, and in-stent thrombosis. Major bleed within 30 days following PCI occurs in approximately 2-3% of patients with either radial or femoral artery approach, though the risk may be slightly greater with femoral access. Periprocedural MI, defined as new or worsening chest pain, electrocardiographic changes, or increased cardiac enzymes within 24 hours following revascularization, is an elusive topic which is thought to result from distal embolization of thrombi following PCI. Periprocedural MI occurs in approximately 6% of cases and is not a predictor of subsequent mortality. In contrast, spontaneous MI, defined as new MI occurring at least 24 hours following revascularization, is a powerful independent predictor of subsequent mortality. Stroke within 30 days of PCI occurs in less than 1% of cases and is commonly thought to occur as a result of thromboembolism from calcium deposits within the aortic root. The occurrence of stroke is not significantly affected by radial versus femoral arterial access. In-stent thrombosis may occur early after PCI and warrants urgent re-evaluation and intervention in the catheterization lab. Finally, a potential chronic complication following stent placement includes in-stent restenosis, which is defined as greater than or equal to 50% stenosis within a previously placed stent or within 5mm of a stent edge. In the era of 2nd and 3rd generation DES, the in-stent restenosis rate is estimated to be approximately 5-10% over a 5-year follow up. In-stent restenosis is treated with either repeat PCI or CABG.
Suggested Readings
- Boden WE, O’Rourke RA, Teo KK, et al. Optimal Medical Therapy with or without PCI for Stable Coronary Disease. N Engl J Med. 2007;356(15):1503-1516.
- Holm NR, Mäkikallio T, Mitchell Lindsay M, et al. Percutaneous coronary angioplasty versus coronary artery bypass grafting in the treatment of unprotected left main stenosis: updated 5-year outcomes from the randomised, non-inferiority NOBLE trial. www.thelancet.com. 2020;395.
- Stone GW, Kappetein AP, Sabik JF, et al. Five-Year Outcomes after PCI or CABG for Left Main Coronary Disease. N Engl J Med. 2019;381(19):1820-1830.
- Xaplanteris P, Fournier S, Pijls NHJ, et al. Five-Year Outcomes with PCI Guided by Fractional Flow Reserve. N Engl J Med. 2018;379(3):250-259.
- Götberg M, Christiansen EH, Gudmundsdottir IJ, et al. Instantaneous Wave-free Ratio versus Fractional Flow Reserve to Guide PCI. N Engl J Med. 2017;376(19):1813-1823.
