MUGA Scan of Apicoaortic Conduit with Incidental Finding of Pseudoaneurysm and Repeat Scan After Aneurysmectomy.

This is a case of a 77-year-old woman who underwent a multiple-gated acquisition (MUGA) scan to evaluate her cardiac function after initially presenting with chest pain and shortness of breath. The scan revealed the presence of an apicoaortic conduit (AAC) and incidentally found a left ventricular pseudoaneurysm. After aneurysmectomy, the MUGA scan was repeated.

Introduction

An apicoaortic conduit (AAC) is a surgical procedure that is performed to alleviate symptoms caused by severe aortic stenosis and other types of left ventricular outflow tract obstruction (LVOTO). This is accomplished by adding a bypass to the aortic valve by placing a left ventricle connector to the apex of the heart and a conduit containing a bioprosthetic valve anastomosed to the descending thoracic aorta.[1] Cerebral blood supply continues through the native valve and the ascending aorta.[2] One of the complications of this procedure is the formation of a pseudoaneurysm, which has previously been described in a patient with uncontrolled hypertension.[3]

Case Report

A 77-year-old woman with a medical history of severe aortic stenosis status post AAC and chronic obstructive pulmonary disease presented to the hospital for chest pain and shortness of breath. Her vital signs, including blood pressure and heart rate, were within normal limits during her hospital stay. The laboratory tests, including routine blood tests and cardiac enzymes, were nonsignificant. Computed tomography (CT) angiography of her chest confirmed the AAC placement and ruled out acute pulmonary embolism [Figure 1]. To evaluate cardiac function and to assess the probable occlusion of the AAC, a multiple-gated acquisition (MUGA) scan was performed that showed blood flow to the ascending aorta and the aortic arch, the AAC to the descending aorta [Figure 2, black arrow], and an incidental finding of a pseudoaneurysm [Figure 2, white arrow]. The phase analysis [Figure 3] showed only two peaks, likely due to synchronous conduction of the atria and the pseudoaneurysm (first peak). The patient, subsequently, underwent aneurysmectomy and was discharged home. A follow-up MUGA scan after aneurysmectomy was performed, which showed blood flow to the aortic arch and the AAC [Figure 4, black arrow]; the pseudoaneurysm was no longer seen, and the patient was noted to be asymptomatic at that time. The phase analysis performed after aneurysmectomy showed an expected two distinct peaks corresponding to the ventricular conduction and atrial conduction, respectively, [Figure 5].

Figure 1

CT angiography of the chest, which confirmed the AAC placement and ruled out acute pulmonary embolism

Figure 2

MUGA scan showing blood flow to the ascending aorta and the aortic arch, the AAC to the descending aorta (black arrow), and an incidental finding of a pseudoaneurysm (white arrow)

Figure 3

Gray scale and color images of the phase analysis, before aneurysmectomy, showing two peaks on the histogram. The first peak is likely to be the result of synchronous conduction between the atria and the pseudoaneurysm, which can explain the absence of three distinct peaks. The second peak represents ventricular conduction

Figure 4

MUGA scan after aneurysmectomy, showing blood flow to the aortic arch and the AAC (black arrow); the pseudoaneurysm is no longer seen

Figure 5

Gray scale and color images of the phase analysis, after aneurysmectomy, showing two peaks on the histogram. The first peak represents ventricular conduction and the second peak represents atrial conduction

Discussion

Historically, AAC has been performed on those patients who are considered to be at a high risk or those ineligible for conventional aortic valve replacement. The use of this technique is rare but has been increasing among the elderly population, given the prevalence of comorbidities that preclude aortic valve replacement, the most common of which are a severely calcified “porcelain” aorta and previous coronary artery bypass grafts preventing aortic root manipulation.[4] Successful performance of this procedure has also been described in other types of LVOTO such as hypertrophic obstructive cardiomyopathy,[56] tunnel subaortic stenosis, aortic annular hypoplasia, and tubular supravalvular aortic hypoplasia.[7] One of the complications that can arise after this procedure is the formation of a pseudoaneurysm, which has been described in a patient with uncontrolled hypertension that resulted in tearing of the myocardium and dehiscence of the left ventricle connector, and which was successfully repaired by surgery.[3] Another complication is stenosis or occlusion of the AAC,[6] which we assessed in our patient. Previous imaging investigations, such as with cardiac magnetic resonance imaging (MRI) and multidetector CT, have shown predictable blood flow patterns between the native valve and the conduit,[89] which is associated with normal ventricular volumes and function, and good blood flow through the conduit. To the best of our knowledge, this is the first time an AAC has been imaged with a MUGA scan. This scan incidentally revealed a pseudoaneurysm and was repeated after aneurysmectomy. We believe that the MUGA scan is an excellent cardiac imaging technique and should be considered in patients with AACs to reliably and accurately assess their cardiac structure and function and the patency of the conduit, especially in those with conditions that place them at a high risk or preclude them from undergoing MRI or CT studies (e.g. pacemakers, borderline renal function, and severe iodinated contrast allergy).