Incidental congenital coronary artery vascular fistulas in adults: Evaluation with adenosine-13N-ammonia PET-CT

ARTICLE HIGHLIGHTS

Research background

Congenital coronary artery fistulas (CAFs) are uncommon coronary artery vascular anomalies which are often incidentally found during coronary angiography (CAG) performed for suspected atherosclerotic coronary artery disease (CAD). Moreover, most asymptomatic patients are diagnosed with CAFs during evaluation for cardiac murmur. Nowadays, congenital CAFs are increasingly detected due to the widespread use of non-invasive techniques such as echocardiography and computed tomography coronary angiography (CTCA). Functional assessment and determination of the clinical significance of CAFs is of great importance for therapeutic decision-making. The choice of treatment strategy depends on the size and location of the fistula, the magnitude of left-to-right shunt and the characteristics of the fistulous tract. Many diagnostic modalities are currently used to evaluate the functional characteristics of the fistula, including non-invasive methods such as Doppler echocardiography, CTCA and radionuclide angiography, and invasive methods such as right heart catheterization and fractional flow reserve (FFR), among others. In the current study, the role of positron emission tomography computed tomography (PET-CT) is described in an observational setting. We aimed to determine the impact of the fistula on the clinical status of the patient, in addition to whether PET-CT can be used to assess the functional status of the fistula. This information was used to determine the best therapeutic strategy, which included monitoring, conservative medical management (CMM), transcutaneous catheter embolization or surgical ligation (SL). In general, echocardiography represents the first diagnostic imaging approach, but it may be limited by an inappropriate acoustic window. Modern echocardiography equipment has greater sensitivity, which explains why congenital CAFs are frequently diagnosed by this method. Echocardiography can be used to diagnose and evaluate the hemodynamic significance, anatomy and physiopathology of CAFs. CTCA is a widely used technique that can be used for morphological and functional analyses, as well as for perfusion studies of CAFs. CTCA allows for comprehensive cardiac evaluation, providing morphological and functional data on coronary circulation and myocardial perfusion status, as well as anatomical images. Electrocardiography (ECG)-gated cardiovascular computed tomography may play an important role in the evaluation of the origin, pathway, termination and morphology of the fistula in relation to the adjacent anatomical structures, as well as cardiac morphology and contractility. Cardiovascular magnetic resonance does not use ionic radiation and plays a crucial role in determining myocardial wall viability, characterizing the myocardial tissue and its morphology, as well as providing detailed data related to cardiac function, estimated blood flow within the fistula and the anatomical characteristics. Myocardial perfusion imaging (MPI) is used to identify abnormalities in cardiac and pulmonary circulation, providing the Qp: Qs ratio is required to diagnose and quantify left-to-right shunt, and to assess myocardial perfusion defects that occur as a result of segmental hypoperfusion caused by the fistula-bearing vessel. Myocardial perfusion single-photon emission computed tomography (SPECT) is used to detect myocardial ischemia and to stratify the risk of experiencing a cardiac event in patients with CAFs. The hemodynamic significance of this modality remains unclear. The closure technique for congenital CAFs will be chosen after thorough diagnostic imaging and functional investigation has been performed to assess the hemodynamic and functional significance of the fistula, its anatomical morphology, and its impact on the clinical status of the patient.

Research motivation

The aim of this study was to review and present the current data on non-invasive and invasive diagnostic methods used to evaluate the anatomical morphology and functional significance of CAFs. Medical imaging is important for assessing the location and size of CAFs.

Research objectives

We assessed the hemodynamic impact of CAFs using ¹³N-ammonia PET-CT imaging under pharmacological adenosine-induced stress and at rest. Future research in a larger group of symptomatic and asymptomatic patients with a greater magnitude of left-to-right shunt is warranted.

Research methods

This was an observational study of 11 subjects with congenital CAFs that had been incidentally found during CAG performed for suspected atherosclerotic CAD. In all patients, physical examination, ECG, echocardiography, chest X-ray and laboratory investigation were performed. The patients were collected from three non-academic hospitals in the West and East regions of the Netherlands. FFR was not measured due to a lack of interventional cardiology facilities in these non-interventional hospitals. Different fistula characteristics were delineated using coronary angiographic imaging techniques. Five subjects underwent pharmacological adenosine stress/rest ¹³N-ammonia PET-CT to assess the hemodynamic impact of the fistula. PET-CT was performed in a different academic center. PET-CT is considered a superior diagnostic modality as it provides data on the metabolic status of the myocardial tissue.

Research results

The patients involved in this study had a variety of clinical presentations, including limited posterior non-ST-elevation myocardial infarction (MI), angina pectoris and chest pain (n = 6), dyspnea upon exertion (n = 3), and an asymptomatic presentation with abnormal resting electrocardiogram (n = 1). One patient presented with palpitation, ischemic cerebrovascular accident, paroxysmal atrial fibrillation and non-sustained ventricular tachycardia. Another patient presented with exercise-induced non-sustained ventricular tachycardia. Previous MI was reported in two patients. The physical examination was unremarkable in seven patients. Apical systolic murmur was heard in one patient, and systolic ejection murmur was heard in the second intercostal space in three other patients. Although continuous cardiac murmur is usually present in patients with CAF, no continuous murmur was heard in the current group of patients. In this case series, the body mass index of subjects ranged between 21.1 to 33.4 kg/m², with four patients classified as normal weight, five as overweight and two as obese. The electrocardiogram demonstrated sinus rhythm in 10 patients and permanent atrial fibrillation in one patient. Echocardiography revealed dilated coronary sinus in one patient. None of the patients showed pulmonary hypertension, with normal results for right ventricular systolic pressure. There were 10 single-sided and one double-sided fistulas. All fistulas were of the coronary vascular type, terminating into the pulmonary artery (n = 11) or coronary sinus (n = 1), and originating from the LAD (n = 8), right coronary artery (RCA, n = 2) or left circumflex coronary artery (LCx, n = 2). In regard to the characteristics of the fistula (origin, pathway and termination), the origin and pathway of the fistulous vessels was plural in most fistulas (8/12, 67% and 9/12, 75%, respectively). Multiplicity was common among the different fistula components (22/36, 61%). In contrast, single (7/12, 58%) termination of the fistulous vessels was more common than multiple (5/12, 42%) termination of fistulous vessels. The termination was equally distributed between single (6/12, 50%) and multiple (6/12, 50%) fistulous vessels. Multiplicity was common among the different fistula components (23/36, 64%). Tortuosity of the pathway was found in eight fistulas (8/12, 67%). A dilated RCA was found in one patient, and large and small aneurysmal formation was present in two patients. The presence of tortuosity and multiplicity of the fistulous tract meant that percutaneous intervention would be very challenging. In patient 2, who had symptomatic significant CAD, SL of the fistula was performed in combination with coronary artery bypass grafting. The characteristics of the fistula components in this patient were multiple origin and termination with multiple-tortuous pathways, which meant the percutaneous approach could not be used. In four patients (patients 4, 7, 8 and 11), PET-CT showed no flow restrictions. Thus, CMM could be implemented, avoiding the need for fistula closure either transcutaneous or surgically. The adenosine stress/rest ¹³N-ammonia PET-CT performed in five subjects demonstrated homogenous distribution of perfusion in two patients, and no perfusion defects in two patients. One patient showed diffuse, reversible reduction in perfusion in the apical and antero-septal regions, and also partly in the basal anterior segment. In another patient, perfusion of the left anterior descending coronary artery (LAD) area was slightly lower than the inferior segment, but it was equal to the lateral wall. Normal perfusion with reduced left ventricular ejection fraction (rest 33%, stress 39%) was probably underestimated in one patient. In these five patients, the mean global stress/rest ratio was 2.9 (range 2.33-3.90). The mean regional stress/rest ratio was 3.0 for the LAD (range 2.35-4.50), 2.9 for the RCA (range 2.49-3.60) and 2.8 for the LCx (range 2.36-3.20). Blood flow through the LAD was slightly higher than through the RCA and LCx. Absolute flow quantification revealed normal myocardial perfusion with high flow in the LCx, which was the fistula-related vessel, compared to the flow of the RCA and the LAD, indicating successful PTE closure procedure of the fistulous vessel. On the other hand, semi-quantitative analysis revealed normal perfusion in two patients and a reduction in diffuse perfusion in the other two patients.

Research conclusions

The hemodynamic characteristics of incidentally found CAFs are of great importance to guide decision-making for whether to treat patients or perform periodic monitoring. Pharmacological adenosine stress/rest ¹³N-ammonia PET-CT in patients with incidentally found congenital CAFs provided adequate and clear information regarding the hemodynamic burden of the fistula in this small patient population. For better diagnosis of incidentally found congenital CAFs, pharmacological adenosine stress/rest ¹³N-ammonia PET-CT should be performed as part of the diagnostic imaging work-up. However, this needs to be confirmed in a large, prospective, international study or registry. In the current study, pharmacological adenosine stress/rest ¹³N-ammonia PET-CT was performed in a limited number of adult patients with incidentally found congenital CAFs. This test is achievable in patients with congenital CAFs. That pharmacological adenosine stress-rest ¹³N-ammonia PET-CT in incidentally found congenital CAFs is currently, in this patient population, can provide adequate and clear answer regarding the hemodynamic burden of the fistula and guiding the clinical decision making. For patients with CAFs, multiple imaging modalities are required to assess the anatomical morphology, hemodynamic significance and behavior of the fistula in order to assist in the choice of therapeutic strategy. Angiographic characterization of the individual fistula components (origin, pathway and termination) may help guide the selection of closure technique, either percutaneously or surgically.

Research perspectives

Further studies on a larger number of patients with congenital CAFs (small or large, symptomatic or asymptomatic, treated or untreated) are required to determine the prospective incidence and other characteristics, such as history and long-term outcomes. In 2018-2019, we are planning to initiate an international registry on CAFs (Euro-CAF Survey) to address the diagnostic and therapeutic issues.