Interventional Transvascular Coronary Arterial Procedures

Once the presence and location of coronary artery stenoses are confirmed, interventional cardiologists can use a variety of methods to improve myocardial blood flow directly. Access to the coronary arteries is through the femoral, brachial, or radial arteries with the use of local anesthesia combined with intravenous analgesia and sedation.^[92] Heparin is administered before the procedure, as noted earlier. Percutaneous transluminal coronary angioplasty (PTCA) involves traversing the stenotic area with a balloon-tipped catheter and compressing the stenosis with the balloon, thereby opening the coronary artery.^[93] Transient coronary artery occlusion occurs during balloon inflation, and the patient's hemodynamic status must be closely monitored. Further analgesia may be necessary because angina may develop during this time. The obligate ischemia limits the stenosis sites that may be treated with this technique to the distal coronary vasculature and, usually, to one- or two-vessel coronary artery disease. These limitations are changing as the technology of angioplasty, coronary stents, and extracorporeal circulation allows treatment of more severely affected patients in the catheterization laboratory, as discussed later. More recently, PTCA has been supplemented by various techniques that remove rather than compress the atheromatous plaques causing coronary arterial stenosis. Coronary atherectomy may be performed either with atherectomy catheters that "shave" the plaque or with the excimer laser.^[94]

During ischemia and frequently during reperfusion after dilation of the stenotic coronary artery, ventricular arrhythmias may develop and require treatment. Hemodynamically significant premature ventricular contractions and nonsustained ventricular tachycardia should be initially treated with lidocaine or, alternatively, with amiodarone. More severe arrhythmias may require cardioversion with the patient under general anesthesia. Rupture of the coronary artery may result in hemopericardium and pericardial tamponade. Pericardial tamponade must be treated with emergency pericardiocentesis, typically guided by transthoracic echocardiography, and it may require emergency operative intervention. Another rare complication of PTCA is coronary artery occlusion, which may result from coronary artery dissection, thrombus within the coronary artery, or vascular spasm caused by dysfunctional coronary artery endothelium. Vascular spasm may often be relieved by the injection of 200 µg of nitroglycerin through the coronary artery. Thrombosis of

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Acute coronary occlusion may not respond to transluminal treatment in the catheterization laboratory and may require emergency coronary artery bypass grafting (CABG). The anesthesiologist must be prepared to manage a very unstable patient if this should occur. The patient may have angina, hypotension, and arrhythmias and may benefit from the insertion of an intra-aortic balloon pump. In addition, the patient may require inotropic support and endotracheal intubation. Nitroglycerin is administered in an effort to improve collateral coronary flow and reduce preload. Adequate preload must be ensured, and monitoring of central pressures may be helpful. If the stenotic or dissected area can be traversed with a guidewire, the cardiologist may be able to leave a perfusing catheter in place to allow some coronary blood flow and limit myocardial ischemia pending surgical revascularization.^[97] Great care must be taken in transport so that this catheter is not dislodged. Time is critical when the patient requires emergency CABG in this situation. The patient must be expeditiously transported to the operating suite and placed on cardiopulmonary bypass as soon as possible for maximal myocardial salvage. Multidisciplinary examination of institutional systems may result in streamlining of the procedure for rapid transport of the patient to the operating suite, thus improving patient outcomes.^[98] Because these patients may be very hemodynamically unstable, their cardiovascular and respiratory status must be continuously monitored.

Results after PTCA and atherectomy procedures are initially excellent. However, restenosis of the dilated coronary arteries has occurred in as many as 30% to 40% of patients and is due to both neointimal thickening and remodeling.^[99] Expandable metallic stents are used to maintain coronary artery patency, with improvement in patency rates. The stents are placed across the area of stenosis after PTCA or atherectomy and remain in place after the procedure.^[100] Current research is focused on further reducing the restenosis rate, including the use of novel mechanical strategies, new systemic drugs to inhibit neointimal proliferation, and drug-coated and drug-eluting stents.^[101]

The use of intracoronary radiation therapy to prevent in-stent restenosis has anesthetic implications. The radiation is believed to prevent neointimal proliferation by breaking DNA strands and hence blocking mitosis.^[102] At least three trials have shown a reduction in the restenosis rate after intracoronary radiation therapy.^{[103] [104] [105]} Currently, intracoronary radiation therapy is the only treatment of in-stent restenosis. From an anesthesia perspective, the therapy has a significant implication. Because of concerns of radiation safety, during deployment of the radiation probe, which is otherwise shielded in a leadlined case, personnel must leave the intracoronary radiation room. Provision for remote monitoring needs to be ensured, similar to that for MRI discussed earlier and similar to the remote monitors for intraoperative radiation therapy (IORT) discussed later.

Patients with evolving myocardial infarction benefit from thrombolytic therapy and, possibly, from PTCA or coronary artery stenting (or both) to restore myocardial blood flow.^{[106] [107]} Such treatment must be administered within 6 to 12 hours to maximize myocardial viability and to reduce morbidity and mortality. These patients may have full stomachs and may be hemodynamically unstable. General anesthesia has been successful in patients who cannot tolerate the procedure because of pain, anxiety, or dyspnea.^[108]

Developments in perfusion technology have increased the portability of the cardiopulmonary bypass machine. It is now feasible to perform extracorporeal circulation in the cardiac catheterization laboratory. This procedure maintains hemodynamic stability during procedures that would otherwise result in unacceptable degrees of myocardial ischemia, such as PTCA and stenting of stenoses of the left main coronary artery. Currently, this procedure is most frequently performed on patients who are not otherwise candidates for CABG surgery, such as those with unacceptably poor ventricular function or distal coronary artery disease that would preclude CABG. ^{[109] [110]} Extracorporeal circulation is established through the femoral artery and vein after induction of general anesthesia and systemic heparinization. Monitoring is the same as for CABG in the operating suite. After the procedure, extubation is performed as soon as the patient's condition allows. The anesthetic technique chosen must provide hemodynamic stability and the potential for early extubation. A balanced anesthetic regimen of fentanyl and a volatile agent with neuromuscular blockade provides these conditions. Patients must be closely monitored for bleeding complications because heparinization is frequently continued after the procedure. Platelet aggregation inhibitors are generally administered. Should complications occur in these patients, who are supported by extracorporeal circulation but who are not surgical candidates, ethical dilemmas may occur. The possibility of complications and the potential treatment options, or lack thereof, must be clearly understood by the patient and by all medical personnel caring for the patient before undertaking such procedures. Clear and open communication is essential in this setting.