Coronary Arteriovenous Fistula (CAVF)

Definition

Coronary arteriovenous fistula (CAVF) is a congenital or acquired anomaly characterized by an abnormal communication between a coronary artery and a cardiac chamber or a great vessel, bypassing the normal myocardial capillary network. This condition results in an arteriovenous shunt, altering coronary hemodynamics and potentially leading to myocardial ischemia, heart failure, or pulmonary hypertension in severe cases.

Embryology and Pathogenesis

Coronary arteriovenous fistulas primarily arise due to failure of regression of embryonic sinusoidal connections between the coronary arteries and the developing cardiac chambers. In most cases, CAVFs are congenital, but they can also be acquired, secondary to thoracic trauma, cardiac surgery, or myocardial infarction.
The coronary arteries most commonly involved are the right coronary artery (50-60%), the left anterior descending artery (30-40%), and, less frequently, the circumflex artery.
The fistula may drain into various structures, with the highest incidence toward the right atrium (40%), the right ventricle (25-30%), and the pulmonary artery (15-20%).

Pathophysiology

The presence of a coronary arteriovenous fistula leads to the phenomenon of coronary steal, where blood preferentially flows through the fistula, a low-resistance pathway, rather than perfusing the myocardial capillary bed. This phenomenon may cause ischemia, especially during physical exertion, reduce coronary flow, and, in severe cases, lead to hemodynamic overload and heart failure.
In some situations, the fistula may result in pulmonary hypertension due to a left-to-right shunt or be associated with an increased risk of endocarditis due to the turbulent flow generated by the abnormal communication.

Clinical Presentation

Many coronary arteriovenous fistulas are asymptomatic, especially if small.
However, in more significant cases, patients may report exertional dyspnea, angina, palpitations, and, in some cases, arrhythmias. On auscultation, a continuous or systolic-diastolic murmur may be detected along the left sternal border, particularly in fistulas with high flow rates.

Diagnosis

The diagnosis of CAVF is primarily based on Doppler echocardiography, which allows the identification of abnormal flow patterns. In some cases, transesophageal echocardiography provides a more detailed visualization, especially of posterior structures. For a more precise characterization of the fistula's anatomy and its connection with the cardiac circulation, coronary CT angiography and cardiac magnetic resonance imaging (CMR) are used. Coronary angiography remains the gold standard for diagnosis and treatment planning.

Treatment

The management of CAVFs depends on size, symptoms, and hemodynamic impact.

• Clinical monitoring: for asymptomatic patients with small fistulas.
• Percutaneous transcatheter closure: the preferred approach for moderate to large fistulas, using coil embolization or vascular occlusion devices.
• Surgical closure: reserved for complex fistulas or those not amenable to percutaneous techniques.

For patients with small, asymptomatic fistulas, the prognosis is excellent. However, untreated large-caliber fistulas may lead to heart failure, myocardial ischemia, ventricular arrhythmias, or sudden death. Early diagnosis and appropriate treatment significantly improve long-term outcomes.

Conclusion

Coronary arteriovenous fistulas are a rare but potentially dangerous anomaly that can impair myocardial perfusion and cardiac function. Early identification and targeted treatment are crucial to preventing complications such as ischemia, heart failure, and pulmonary hypertension. The use of advanced imaging and interventional cardiology techniques has significantly improved the management of these anomalies.

Bibliografia
1. Russo F, et al. "Trattamento percutaneo di fistola coronarica: serve una strategia su misura." Giornale Italiano di Cardiologia, vol. 19, no. 3, 2018, pp. 187-190.
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3. Said SA, et al. "Coronary arteriovenous fistulas: collective review and management of six new cases—changing etiology, presentation, and treatment strategy." Clinical Cardiology, vol. 31, no. 8, 2008, pp. 355-360.
4. Liberthson RR, et al. "Congenital coronary arteriovenous fistula: report of 13 patients, review of the literature and delineation of management." Circulation, vol. 59, no. 5, 1979, pp. 849-854.
5. Urrutia-S CO, et al. "Surgical management of 56 patients with congenital coronary artery fistulas." The Annals of Thoracic Surgery, vol. 35, no. 3, 1983, pp. 300-307.