The Role of Imaging in Adult Tetralogy of Fallot Patients
The past several decades have seen a dramatic rise in the number of adults in the US with congenital heart disease (CHD). According to some estimates, the US patient population is increasing by 5 percent every year, with an estimated 1,250,000 patients as of 2012. The increasing incidence is due at least in part to medical and surgical advances in the 1960s and 1970s that led to improved survival for children with CHD. Occurring in roughly five of every 10,000 newborns, Tetralogy of Fallot is one of the most common congenital defects, affecting up to 0.5 per 1,000 live births. These numbers underscore the importance of subspecialty monitoring of adults, particularly those who have undergone repair for CHD.
Adult TOF can include a range of presentations and consists of cases diagnosed and treated in childhood with sequelae or residual lesions in adulthood, cases diagnosed in childhood but not treated, and new cases diagnosed in adulthood. In each case, diagnosis and treatment can be complicated by age-related factors such as symptoms of acquired heart disease, adding to the need for advanced imaging in managing patients.
TOF is typically treated with surgical repair when the diagnosis is made in infancy or childhood. In the modern era, rarely do patients present unrepaired in adulthood. While survival after surgical repair is generally excellent, patients may suffer late complications. Studies show a three-fold increase in mortality in the third decade post intervention, and 14% of patients manifest significant impairment over several years. To improve long-term outcomes, TOF patients must be monitored through adolescence and adulthood.
Ultrasound is used as the initial screening test for PR in adult TOF patients and is effective as a first-line modality for qualitative assessment of the right ventricle. This method allows real-time visualization of the heart wall in motion, recorded as single images and video clips. However, obtaining comprehensive images of the right ventricle with ultrasound can be challenging due to its unique pyramid-shaped geometry and its location in the chest behind the sternum. Lung and bone block the sound waves, leaving a difficult acoustic window for assessment in many patients. Comparisons of the accuracy of right-heart parameters measured with both ultrasound and MRI in adult-repaired TOF patients have generally shown the benefits of MRI over ultrasound. Studies have shown that systolic function measures by ultrasound do not provide a complete and accurate measure of right ventricular ejection fraction as compared to cardiac MRI. Additionally, it may be challenging to accurately quantify PR echocardiographically; PR may be more precisely quantified by cardiac MRI.
Cardiac MRI is used as a second-line, complementary modality for the evaluation of PR in adult TOF patients who have undergone repair. Introduced in the late 1990s, cardiac MRI is now considered the gold standard for assessment of right ventricle size and function. However, because it uses a powerful superconducting magnetic field, it can pose challenges and contraindications for patients with metallic implants, including some pacemakers and certain other implants.
In recent years, the development of two-dimensional (2D) and four-dimensional (4D) flow-velocity MRI has added measures of blood flow volume and velocity to the unrestricted spatial planes that MRI allows. A key metric is the direct assessment of ventricular volumes of the ventricular chamber (whereas ultrasound only measures blood flow velocities). The volumes of blood in the ventricle (i.e., end-diastolic right ventricular volume), as well as the proportion of blood pumped per beat (i.e., ejection fraction) best predict the appropriate timing for valve repair or replacement. This assessment is accomplished via careful measurement of multiphase datasets and processing of velocity-encoded images. Researchers are currently exploring the possibility of using information derived from 4D flow datasets in patients who have undergone repair for TOF to facilitate efficacious determinations of right ventricle dilation and function.
Cardiac computed tomography (CT) and CT angiography (CTA) can be used to screen for PR in adult TOF patients when cardiac MRI is contraindicated or when additional, complementary information (such as coronary artery anatomy) is needed. CT is also used for pre-procedural planning prior to percutaneous catheter-based valve deployment. Minimally invasive transcatheter-based pulmonary valve replacement requires detailed valve area anatomy to properly size the device prosthesis.
Because they require ionizing radiation, CT and CTA are reserved for adult TOF patients with abnormal first- or second-line screening at high risk of PR and those with a favorable anatomic profile for intervention.
Echocardiography, cardiac MRI and cardiac CT are performed on the main campus of Massachusetts General Hospital in Boston. Echocardiography is also performed as Mass General Imaging - Waltham and Mass General/North Shore Center for Outpatient Care. Cardiac CT is also performed at Mass General Imaging - Waltham. Appointments can be made through Epic (inside the Partners network) or Physician Gateway (outside the Partners network) or by calling 617-726-8396. The office number for the MGH Adult Congenital Heart Disease Program is 617-643-7024 or 617-726-8510.
For further information on the role of CT and MRI imaging in the care of adult patients with TOF, please contact Brian B. Ghoshhajra, MD, MBA, Division of Cardiovascular Imaging, Department of Radiology, Massachusetts General Hospital, at 617-643-0239.
Bhatt AB, Foster E, Kuehl K, et al. (2015). Congenital Heart Disease in the Older Adult A Scientific Statement From the American Heart Association. Circulation 131:00-00.
©2016 MGH Department of Radiology
Janet Cochrane Miller, D. Phil., Co-Author
Gary Boas, Co-Author
Raul N. Uppot, M.D., Editor