Heart dominance is described by which coronary artery branch gives off the posterior descending artery and supplies the inferior wall, and is characterized as left, right, or codominant. The posterior descending artery (PDA) is also known as the posterior interventricular artery because it runs along the posterior interventricular sulcus to the apex of the heart. It is at the apex where it meets the left anterior descending artery that is traveling along the anterior surface of the heart. The posterior descending artery is responsible for supplying the posterior third of the interventricular septum, including the posterior and inferior wall of the left ventricle. The vessel most commonly originates from either the right coronary artery (right dominant), left circumflex artery (left dominant), or both (codominant). There have been physiologic variants described in case reports such as an origin from the left anterior descending artery, referred to as “superdominant.” Estimates are that 70 to 80% of the population is right heart dominant with the posterior descending artery originating from the right coronary artery. Approximately 5 to 10% of the population is left heart dominant with the PDA originating from the left circumflex artery, and about 10 to 20% is codominant with the PDA supplied by both the left circumflex artery and right coronary artery. Small branches from the dominant artery perfuse the atrioventricular node. Theoretically, decreased perfusion to the atrioventricular node may result in dysfunction, adding further significance to the cardiac dominance of the patient.
The posterior descending artery, as with any coronary artery, is subject to possible stenosis or occlusion secondary to atheromatous plaque accumulation or thrombosis. The result of stenosis to the posterior descending artery would be decreased perfusion or even infarction of the posterior third of the interventricular septum, depending on the severity. Therefore, the location of the possible infarction or reduced perfusion is dependent on the cardiac dominance of the individual. For example, a patient that is left heart dominant and suffering from severe stenosis of the proximal left main coronary artery may suffer infarction of the posterior interventricular septum. However, this would not be true in a patient with codominant coronary circulation. A stenotic lesion to the proximal left main coronary artery would result in decreased perfusion to the posterior interventricular septum, but it would still receive blood via the right coronary artery, reducing the risk of an infarct.
In right dominant coronary circulation, the posterior descending artery serves as a collateral vessel to the basal left anterior descending artery through septal perforators, which would mean that a patient with proximal left anterior descending coronary artery stenosis has the additional benefit of possibly receiving supply from the right coronary artery if he or she is right heart dominant. This collateral circulation may be enough to bypass the blockage in the left anterior descending artery to provide enough oxygenated blood to allow the cardiac muscle to survive and recover.
Cardiac dominance plays an essential role in cardiac surgery, particularly coronary artery bypass grafting. Determination of cardiac dominance is through cardiac catheterization which involves insertion of a catheter into the ostium of the left main coronary artery, and the right coronary and injection of radiocontrast dye to allow visualization of coronary arteries. In coronary artery bypass grafting procedure, precise knowledge of patient-specific coronary anatomy is crucial; this is because the surgeon must identify which vessels are suitable to receive the distal anastomosis of the venous graft. For occlusion of the right or left coronary artery, the posterior descending artery may be the choice if suitable dependent on its patency. The venous conduit is then sutured into a portion of the right coronary artery that is distal to the occlusion.
There have been a large number of studies conducted to determine the significance of cardiac dominance on patient outcome and pathology. One study revealed that patients with left coronary dominance have a reduced prognosis in surgical myocardial revascularization. The exact reason remains undetermined, but speculation is that there is an association with collateral circulation seen in right heart dominant patients that is absent in left heart dominant subjects.
Left heart dominance was described to be a high-risk feature for percutaneous coronary intervention as well. Left heart dominant patients undergoing percutaneous coronary intervention have higher in-hospital mortality and more likely to present with symptoms of heart failure, cardiogenic shock, or cardiac arrest.
Left heart dominance in patients undergoing aortic valve replacement for severe aortic stenosis was also shown to be an independent risk factor. There appears to be an increased prevalence of left heart dominance in patients undergoing aortic valve replacement and that the left main coronary artery is significantly shorter than those seen in right heart dominant patients; this may be evidence of a developmental relationship seen in left heart dominant patients between the left main coronary artery and aortic valve. In one study, patients with left dominant coronary circulation were determined to suffer a significantly higher rate of perioperative myocardial infarction compared to right heart dominant or codominant patients.
These studies and trials highlight the significance of determining dominance in coronary artery anatomy within multiple aspects of treating cardiac pathology. The increased risk seems to correlate with left heart dominant circulation, but more research has to be done to determine if different strategies need to be implemented to ensure better outcomes.