A 53-year-old with a history of surgically corrected tetralogy of Fallot (TOF) presented with dyspnea, fatigue, and increased abdominal girth. The patient was cyanotic as an infant and underwent a palliative left Blalock-Taussig (BT) shunt. At eight years of age he underwent corrective surgery with patch repair of a ventricular septal defect and resection of the infundibular region of the right ventricular (RV) outflow tract. The BT shunt was ligated at that time. The patient did well until 2007, when he developed atrial dysrhythmias that were recalcitrant to medical therapy. Ultimately, the patient underwent atrioventricular nodal ablation and bi-ventricular pacemaker placement.
Examination revealed a cachectic-appearing male who was mildly dyspneic at rest. Jugular venous distension was prominent. The lungs were clear to auscultation. Cardiac examination revealed diminished S1 with S3 present. A blowing 2/6 holosystolic murmur and a rumbling 2/4 diastolic murmur were heard at the left lower sternal border. There was a 2/6 holosystolic murmur at the apex. The abdomen was distended with prominent ascites. No peripheral edema was present.
An electrocardiogram (ECG) revealed atrial fibrillation with intrinsic atrioventricular conduction and intermittent ventricular paced complexes. An echocardiogram was performed and demonstrated a dilated and hypokinetic right ventricle by M-mode and 2D assessment. No residual RV outflow tract gradient was identified. There was moderate to severe pulmonic valve insufficiency with an estimated pulmonary artery diastolic pressure of 31mmHg. There was also severe tricuspid valve insufficiency with a peak regurgitant velocity of 5.7m/sec, consistent with pulmonary artery hypertension. There was mild aortic and mitral valve insufficiency with mildly depressed left ventricular (LV) systolic function.
Further imaging of RV size and function was requested for potential surgical replacement of the pulmonic valve. Cardiac magnetic resonance (CMR) imaging is considered the gold standard for evaluation of RV chamber size and function in congenital heart disease.1 Unfortunately, the patient had a bi-ventricular pacemaker, which is a relative contraindication to CMR. The patient was referred for cardiac multidetector computed tomography (MDCT) since recent studies have demonstrated agreement and correlation between cardiac MDCT and CMR in assessing RV size and ejection fraction.2,3 MDCT provided additional information regarding coronary anatomy and post-TOF repair cardiac anatomy, which is essential for surgical planning.
The MDCT protocol for this case was complex due to congenital heart disease with multiple prior cardiac surgeries and atrial fibrillation with irregular R-R intervals with intermittent ventricular pacing. Metoprolol, 100mg by mouth, was given two hours before the scan. Diltiazem, 20mg intravenously (IV), was administered prior to the scan. The patient continued to have intermittent intrinsic conduction and the lower rate of the pacemaker was increased to 80 paced beats per minute to achieve a regular R-R interval. A non-contrast ECG-gated CT of the heart and great vessels was first performed using 120kV with mAS of 300 at 40% phase. Next, a contrast cardiac MDCT study was performed with 125ml of iopamidol at 6ml/sec followed by 50ml of 0.9 normal saline at 5ml/sec. Slice thickness was 0.8mm with the window set from the lower neck to just below the heart. The scan was performed using 120kV with mAS 700 using 0, 35, 40, 45, 70, 75, and 80% phases. A one-minute delayed scan was performed using the same window at 120kV with mAS 300 at 40% phase. All scans were performed with dose modulation. Multiple cardiac phases from 0 to 90% at 10% intervals were created in post-processing.
There was normal origin and course of the coronary arteries without stenosis. Coronal images demonstrate the remnants of a BT shunt (see Figure 1). RV dimensions were measured from an apical orientation analogous to standards set out in the American Society of Echocardiography guidelines.4 RV size was severely enlarged with minor axis dimensions at the base and mid-chamber of 68.1 and 70.8mm, respectively (see Figure 2A). RV chamber length from base to apex was 128.5mm (see Figure 2A). RV area was 723cm2 (see Figure 2B). RV volumes by Simpson’s disc method were obtained from an area of 28 equal-thickness discs and summed to obtain a total volume in both systole and diastole (see Figure 3). The RV end-diastolic volume was 743ml and the RV end-systolic volume was 539ml. RV outflow tract dimensions appeared normal with a minor axis of 33–37mm and a major axis of 42–51mm. RV hypertrophy was suggested, with a diastolic wall thickness of 2.9–4.8mm. Visually, there was global hypokinesis of the RV, with 27% ejection fraction by volumetric assessment (see Figure 4).
Adult TOF patients can develop RV dysfunction and ultimately failure due to progressive worsening of pulmonary valve insufficiency. The presence of RV dysfunction and enlargement needs to be carefully evaluated to determine the timing of the intervention.5 MDCT has been used in the evaluation of RV size and function and has been shown to provide a slight (4%) but consistent overestimation of volume and dimensions and underestimation of ejection fraction compared with CMR.3,6 These discrepancies may be explained through differences in imaging physics between each modality, which affects the ability to identify endocardial borders and valvular planes.
In conclusion, MDCT was able to provide measurements of RV size and function in a patient with repaired TOF who could not undergo CMR. The information obtained from this study was essential for the treating physicians in terms of developing a treatment strategy. The patient, at present, is being evaluated for heart–lung transplantation.