A coronary artery fistula is an abnormal connection between a coronary artery and a cardiac chamber (“coronary cameral fistula”) or another vessel (“coronary arteriovenous fistula”) such as a systemic vein, pulmonary vein, or pulmonary artery. About 90% of fistulae terminate on the right side of the heart, most commonly connecting to the right ventricle followed by the right atrium, pulmonary artery, coronary sinus, left atrium, and left ventricle. These abnormal connections may consist of single or multiple points of entry, a plexiform communication, or a side-to-side opening. Around 60% of fistulae originate from the right coronary artery or a branch thereof, and 40% come from the left coronary artery, circumflex, or more distal left sided branches. Approximately one in five patients with a coronary artery fistula have additional congenital heart disease, including pulmonary atresia with intact ventricular septum, tetralogy of Fallot, transposition of the great arteries, ventricular septal defect, atrial septal defect, bicuspid aortic valve, and coarctation of the aorta. Rarely, a fistula may be acquired following myocardial resection (e.g. for relief of right ventricular outflow tract obstruction), cardiac biopsy, ablation, tumor, trauma, or myocardial infarction.
Fistulae occur in about 2 in 1000 people in the general population, and comprise approximately 0.2-0.4% of congenital heart disease. There is no race or gender predominance.
Fistulae are thought to represent the persistence of coronary sinusoids or incomplete reabsorption of myocardial trabeculations.
Clinical presentation of a coronary artery fistula depends on size and the point of termination. Many small fistulae are often incidentally identified on imaging obtained for other indications and remain asymptomatic. Large fistulae may result in enough of a volume load to cause chamber enlargement or heart failure symptoms as early as infancy. Less significant fistulae may present with a murmur, dyspnea, fatigue, or angina in adolescence or, more typically, adulthood. Other potential long term complications include premature coronary artery disease, endocarditis within the fistula, fistula rupture causing hemopericardium, and pulmonary hypertension. For hemodynamically significant fistulae, both transcatheter occlusion and surgical ligation are considered. Patients may have residual flow or chronic coronary microvascular dysfunction following intervention and thus require long-term follow up.
The hemodynamic impact of a fistula stems from 1) distal coronary insufficiency, and 2) shunt, volume load, or runoff that varies depending on the receiving chamber or vessel.
Regarding the former, a coronary “steal” phenomenon whereby myocardium distal to the fistula is deprived of oxygen is most evident during times of increased myocardial demand such as exercise, and may be exacerbated in adults with coexisting coronary artery disease. Angina can be a presenting symptom but critical ischemia is rare.
Regarding the latter, fistulae that drain into the right heart and pulmonary artery behave like other left-to-right shunts, with progressive chamber dilation and the potential for increased pulmonary blood flow and eventual development of pulmonary hypertension. Fistulae draining into the left atrium behave similarly to mitral regurgitation, with progressive left heart dilation and heart failure symptoms. Those draining into the left ventricle share the physiology of other runoff lesions such as aortic regurgitation or PDA.
Goals of the echocardiography exam
In 2D echo, a dilated proximal coronary artery may be the first clue to the presence of a fistula. The fistula itself is rarely visualized in 2D unless it is quite large, but color Doppler may reveal abnormal diastolic flow. In addition to identifying the presence and potential course of a fistula and evaluating chamber enlargement, the goals of echo include:
Identifying the origin of each major coronary artery (LAD, circumflex, right)
Identifying the proximal course of each major coronary artery
Demonstrating direction of flow in each major coronary artery by color Doppler
Evaluating global and regional LV function
Evaluating for mitral regurgitation
Identifying associated defects
Often, if an echo raises concern for a fistula, a CT, MRI, or coronary angiography may be pursued for definitive imaging.
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