Postoperative Imaging of Ischemic Cardiac Disease

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CHAPTER 59 Postoperative Imaging of Ischemic Cardiac Disease

Congestive heart failure, the most common admitting diagnosis for patients older than 65 years in the United States,1 continues to increase in incidence and prevalence, with more than 500,000 new cases of chronic heart failure diagnosed yearly. The most common cause of heart failure is ischemic cardiomyopathy; the second most common cause is dilated cardiomyopathy. The diagnosis, management, treatment, and rehabilitation of patients suffering from ischemic heart disease represent a large percentage of health care costs. Current interventions for management and treatment of end-stage ischemic heart disease include aggressive medical management, extracorporeal circulatory support, percutaneous left ventricular assist device placement, implantable ventricular assist device placement, coronary artery revascularization, mitral valve repair or replacement, scar ablation, passive epicardial restraint, surgical ventricular restoration, and heart transplantation. Combinations of these surgical interventions are sometimes used, depending on the patient’s needs.

In this chapter, we cover common surgical options (other than coronary artery bypass graft surgery) for ischemic heart disease and its complications. These surgeries include the ventricular restoration procedure (Dor procedure), cardiac assist device, and heart transplantation. Although mitral valve repair involving mitral annuloplasty is considered an option in the treatment of patients with ischemic or nonischemic dilated cardiomyopathy, it is not widely practiced. This surgery is considered for patients with secondary mitral regurgitation (normal mitral valve anatomy) due to a dilated ventricle from ischemic or other causes that results in displacement of papillary muscles and dilation of the mitral annulus.

PREVALENCE, EPIDEMIOLOGY, AND BACKGROUND

Of 5.3 million Americans suffering from heart failure, about 2.8 million will die within a year. Between 2000 and 4000 Americans are on waiting lists for heart transplants at any given time, and according to the United Network for Organ Sharing, approximately 2000 heart transplants are performed every year. About 10% to 20% of patients on the heart transplant waiting list die while awaiting the opportunity for receipt of a transplant. According to the United Network for Organ Sharing, 5-year post–heart transplantation survival rates for heart status 1A, 1B, and 2 are 68.7%, 72.7%, and 74%; 1-year survival rates for heart status 1A, 1B, and 2 are 85.7%, 87.3%, and 90.6%.

For patients obtaining ventricular assist devices as a bridge to transplantation or destination therapy, 1-year survival rates have been reported to be 52% compared with 25% for a medically treated cohort of patients; the 2-year survival rate is 23% compared with 8% for a medically treated cohort of patients.2

In one study including 1198 patients, 5-year survival rates of patients undergoing surgical ventricular restoration with concomitant coronary artery bypass graft or mitral valve surgery were 69.9% ± 4.7% for New York Heart Association (NYHA) class III patients.3 Results of the STICH (Surgical Treatment for Ischemic Heart Failure) trial, a recently completed randomized surgical versus medical trial, will help clarify indications for coronary revascularization, surgical ventricular restoration, and medical therapy. Alternative therapies to heart transplantation will continue to be important because of the yearly increasing gap between demand and supply of hearts.

Ventricular Assist Device

The ventricular assist device (VAD) is an implantable electromechanical cardiovascular support device for patients with heart failure to improve cardiac output and thereby to achieve adequate circulatory status and to maintain effective end-organ perfusion. Common indications are cardiogenic shock due to myocardial infarction, postcardiotomy cardiogenic shock, and bridge to heart transplantation for patients with ischemic heart failure. It may be used permanently as a destination therapy for patients who are not eligible for heart transplantation. A temporary percutaneous left VAD (LVAD) can provide support during complex percutaneous coronary interventions. Contraindications to VAD placement include very short stature and emaciated, thin patients.

Examples of short-term temporary percutaneous LVADs are the CardiacAssist, Inc., TandemHeart; Abiomed Impella, Abiomed BVS 5000; Medtronic Bio-Medicus Bio-Pump; Terumo Sarns Centrifugal System; St. Jude Medical Lifestream centrifugal pump; Levitronix CentriMag LVAS; and intra-aortic balloon pump counterpulsation.

Long-term VADs include pulsatile (first-generation) and nonpulsatile (second-generation) devices and can provide support for 6 to 12 months, with much longer reported durations (even up to 2 to 3 years). In general, nonpulsatile devices, such as the MicroMed DeBakey VAD pump unit, MicroMed DeBakey HeartAssist 5 pump (for pediatric and adult implantation), Thoratec HeartMate II VAD, and Jarvik 2000, are continuous flow pumps that require some baseline native cardiac reserve in case of device mechanical failure. These are simpler to implant and also smaller and quieter than pulsatile devices.

The first-generation pulsatile devices, such as WorldHeart Levacor VAD, Thoratec HeartMate XVE, WorldHeart Novacor LVAS, Thoratec IVAD (implantable ventricular assist device), and Thoratec PVAD (paracorporeal ventricular assist device), are not continuous flow pumps and simulate the cardiac cycle.

Three total artificial hearts are the SynCardia Systems, Inc., CardioWest Total Artificial Heart; the Abiomed AbioCor system; and the Arrow LionHeart LVAS. Newer generation nonpulsatile VADs include the Berlin Heart INCOR LVAD; Ventracor VentrAssist system; Thoratec HeartMate III, HeartWare HVAD, and MVAD; Terumo DuraHeart LVAS; and Cleveland Clinic Foundation CorAide blood pump.

Surgical Ventricular Restoration: Dor Procedure

The ventricular restoration procedure (Dor procedure or endoventricular circular patch plasty) is an established surgical option for patients with ischemic dilated cardiomyopathy with left ventricle aneurysms and akinetic or dyskinetic myocardial segments. It can be used as an alternative treatment because of limitations of cardiac transplantation and VADs, such as donor organ shortage and financial restraints.

The Dor procedure involves excision of akinetic or dyskinetic and nonviable myocardium of the left ventricle and patch repair of the distal left ventricular cavity, thus restoring the normal elliptical shape of the left ventricle from a spherical dilated heart. The opening of the ventricle is closed by Dacron patch or stitches.4 The restoration of ventricular volume reduces the stress on the ventricular wall, reduces myocardial oxygen consumption, and increases wall contractility and compliance.5 Associated mitral valve regurgitation or intraventricular thrombi are corrected simultaneously. Before surgery, appropriate coronary revascularization procedures, including grafting of the left anterior descending coronary artery, which supplies a high portion of the septum, should be performed.5 Perioperatively, appropriate ventricular volume is restored in the septal and anterior wall without deforming the chamber that will result in neither restrictive nor dilated cardiomyopathy. Care is also taken to achieve an optimal postoperative ventricular short-axis/long-axis ratio; otherwise, mitral regurgitation can result.

The first reported surgery to treat left ventricle aneurysms by Cooley and colleagues involved excision of the thinned segment with linear closure of the free edges.6 Alternative approaches were developed by Dor and Jatene; an intraventricular patch was placed to exclude akinetic and nonresectable areas. The Dor procedure, or endoventricular circular patch plasty, was first performed in 1985.4 Some of the criteria for the Dor procedure are ischemic dilated cardiomyopathy involving one third or more of the ventricular perimeter that causes a spherical dilated left ventricle with akinetic or dyskinetic portions of the septum and anterior wall with end-diastolic volume above 100 mL/m2, reduced ejection fraction (<20%), left ventricular regional asynergy (>35%), and symptomatic patient (angina, heart failure, arrhythmias, and inducible ischemia). Contraindications to the procedure are systolic pulmonary artery pressure above 60 mm Hg without associated mitral regurgitation, severe right ventricular dysfunction, and regional asynergy without ventricular dilation.

Cardiac Transplantation

Cardiac transplantation has been established as the most reliable permanent treatment option for patients with deteriorating heart failure due to ischemic dilated cardiomyopathy despite maximum medical therapy and other revascularization techniques. The most commonly performed type is orthotopic cardiac transplantation, in which the recipient heart is removed except for the posterior aspect of the atrial cuffs. The donor heart is then attached to the recipient’s atria, and the donor’s ascending aorta and main pulmonary artery are anastomosed end to end to the severed ends of the recipient’s ascending aorta and main pulmonary artery, respectively.7

Indications include severe ventricular dysfunction with a life expectancy between 12 and 18 months and lack of improvement in ejection fraction from medical therapy or resynchronization therapies. The criteria include NYHA classification III or IV status, age younger than 65 to 70 years, and reproducible image of less than 14 mL/kg per minute,

Patients with nonischemic causes of heart failure, such as hypertensive heart disease, myocarditis, idiopathic cardiomyopathy, valvular heart disease, congenital heart disease, and peripartum cardiomyopathy, can also benefit from cardiac transplantation.8 Contraindications to heart transplantation may include AIDS, active systemic infection, malignant disease, irreversible pulmonary hypertension, irreversible secondary organ failure, comorbid life-threatening conditions, active substance abuse, psychiatric history likely to result in noncompliance, cachexia or obesity, chronic obstructive pulmonary disease, renal insufficiency, continued smoking, and severe osteoporosis.

Heterotopic cardiac transplantation is performed in patients with potentially reversible cardiac dysfunction, high pulmonary vascular resistance, or small donor hearts.9 The donor heart is placed anterior to the right lung along the right side of the native heart, and the two left atria are anastomosed, resulting in a common left atrium. The orifices of the donor inferior vena cava and right pulmonary veins are closed. The donor ascending aorta is anastomosed to the recipient aorta in end-to-side fashion, and the donor main pulmonary artery is combined with a Dacron graft, resulting in an end-to-side anastomosis with the recipient main pulmonary artery. The donor superior vena cava and right atrium are connected to the native right atrium, allowing systemic venous return to pass into either the native or the donor right ventricle. Chambers involved in functioning include the right ventricle of the recipient and the left ventricle of the donor.

POSTOPERATIVE ASSESSMENT

Imaging is paramount in assessment of postoperative patients for complications of these surgical procedures. Immediate complications include hematoma, effusions, pneumothorax, and pulmonary embolism. Delayed and late complications include mediastinitis, conduit thrombosis in the VAD, intracardiac thrombus, mitral regurgitation, restricted left ventricular cavity, and patch dehiscence in the Dor procedure; and pulmonary infections, anastomotic dehiscence, aortic pseudoaneurysms, allograft rejection, coronary arteriopathy, and post-transplantation lymphoproliferative disorder in cardiac transplantation.

Radiography, echocardiography, and computed tomography (CT) are used for immediate postoperative imaging of the VAD, surgical ventricular restoration, and cardiac transplantation, depending on the indication and postoperative complications. Cardiac magnetic resonance imaging (MRI) with delayed enhancement technique is the best imaging modality to assess transplanted patients for rejection; however, cardiac CT and catheter angiography are particularly useful for evaluation of coronary arteriopathy.

Specific Complications

Ventricular Assist Device

Right-sided heart failure may be due to adverse effects of the LVAD on the interventricular septum, increased pulmonary pressure due cardiopulmonary bypass or massive blood transfusions, and right coronary artery disease.1 After the perioperative period, infection related to the VAD, thromboembolism with infarction, and limited reliability of the VAD remain the most important concerns. Patients with a VAD are more susceptible to infection because of tracking along subcutaneous drivelines for connecting batteries and controllers, leading to entry and exit site infection, driveline infection, or pump infection. Pump infection may require removal of the device and hence is of the greatest concern.1 Thrombus can sometimes be seen in the cardiac chambers or inflow and outflow cannulas. Thromboembolism and resultant infarction of lung, brain, or systemic organs may occur after VAD placement, although the HeartMate device is believed to have less chance for this development because of the textured surface of the blood-containing chamber by a polyurethane diaphragm, which leads to pseudointima formation.10 Aortic dissection at the level of the ascending aorta can result from high-velocity blood injected against the aortic wall. Device reliability depends on the type of device; it is 1 to 3 years for pulsatile pumps and about 5 years for miniaturized axial flow pumps. However, because the VAD does not fail catastrophically, further treatment by device exchange or transplantation can be warranted.1

Cardiac Transplantation

Early postoperative complications (between 0 and 30 days) are related to surgical complications, including cardiac ischemia, pulmonary edema, and anoxic brain injury and thromboembolic events. Intermediate postoperative complications (between 1 month and 12 months) mainly include acute allograft rejection and infection. Allograft rejection is manifested usually between 2 and 12 weeks after transplantation.9 The time of greatest immunosuppression is during the first 3 months after transplantation. Bacterial (predominantly aerobic gram-negative rods), viral, and fungal infections occur within the first month and often affect the lungs.

Mediastinal infection can lead to weakening of suture lines and cause aortic dissection and pseudoaneurysm formation. Late complications (after 12 months) resulting in death include transplant-associated coronary artery accelerated graft atherosclerosis, malignant disease, infection, transplant rejection, aortic allograft rejection, and cerebral infarctions.12

Coronary allograft vasculopathy or atherosclerosis is caused by immune-mediated and nonimmunologic injury,7 which affects half of patients within 5 years of transplantation and is characterized by diffuse concentric intimal thickening of both proximal and distal coronary arteries. The major risk factors for late mortality from coronary allograft vasculopathy include ischemic heart disease, younger recipient age (but older than 20 years), black race, cigarette use within 6 months of listing for transplantation, older donor age, and development of coronary artery disease during the first post-transplant year.13 Malignant neoplasms are likely to be secondary to long-term immunosuppression and include lymphomas, acute leukemia, visceral tumors, Kaposi sarcoma, gynecologic cancers, primary lung carcinoma, skin cancer (predominantly squamous cell cancer), and post-transplant lymphoproliferative disorder.9

Other complications are related to long-term corticosteroid use and immunosuppression. These include osteoporosis, vertebral insufficiency fractures, and lipomatosis.8

CLINICAL PRESENTATION

Perioperative bleeding and air accumulation can draw early attention on serial radiographs or by symptoms such as acute-onset breathlessness and dyspnea in the immediate postoperative period.

Patients with mediastinitis are often unwell and may have fever, tachycardia, chest discomfort, sternal tenderness, and leukocytosis. Discharge from the sternotomy wound with delayed healing may be indirect evidence of ongoing sternal osteomyelitis or a mediastinal infection or collection.9

Fever or lethargy may be the first indicator of internal systemic infection. If it is associated with breathlessness, productive cough, and pleuritic chest pain, it can be a warning symptom of community-acquired or opportunistic pulmonary infections, which are quite common in the postoperative period because of immunosuppression. Patients with infective (mycotic) pseudoaneurysms may be asymptomatic or may present with fever, lethargy, and chest pain.9 Pulmonary embolism is typically manifested with sudden-onset breathlessness, chest pain, tachycardia, and hypoxia.

Focal neurologic deficits or sudden-onset peripheral vascular ischemia may indicate a thromboembolic phenomenon; imaging is recommended to assess for intracardiac thrombus, especially in patients with the Dor procedure. In patients with a VAD, contrast-enhanced CT is preferred to assess for intraconduit thrombus formation.

Sudden-onset chest pain may be a common manifestation of a variety of causes, such as aortic dissection, intramural hematoma, aortic pseudoaneurysm formation, coronary atherosclerosis, pulmonary embolism, new-onset myocardial infarction, ventricular wall perforation, and cardiac arrhythmias. Cross-sectional imaging, such as CT and echocardiography, is essential for early diagnosis and treatment of these conditions.

In heart transplantation, a common complication in the postoperative period is impending rejection, which may be asymptomatic or can be manifested by dyspnea, palpitation, fatigability, weakness, syncope and signs suggestive of hypotension, worsening of cardiac function, and increasing heart failure.9

Clinical manifestations of coronary vasculopathy include myocardial infarction, graft failure, arrhythmias, and sudden death. It starts distally in small coronaries and progresses proximally to epicardial vessels without formation of collaterals.7 Because of the difficulty in preventing this complication and the clinically silent presentation, routine surveillance has been advocated for detection and early intervention by revascularization procedures.7

New-onset back pain in patients receiving corticosteroids should suggest osteoporosis, vertebral fractures, intervertebral diskitis, or internal malignant disease with bone metastases. Gastrointestinal complications, such as peptic ulcer, diverticulitis, and organ perforation, may go unnoticed because of the effect of corticosteroids, which may mask signs and symptoms.8 A high index of clinical suspicion and appropriate timely imaging would help in identifying these serious pathologic processes.

IMAGING INDICATIONS AND ALGORITHM