Balancing a single-ventricle circulation: ‘physiology to therapy’

The parallel supply of the pulmonary and systemic circuits complicates the management of single-ventricle lesions. Achieving a balance between the two limbs of the circulation forms the basis of optimizing the systemic oxygen delivery, with the oxygen availability being highly sensitive to alterations in pulmonary/systemic blood flow ratio (Q_p/Q_s). The identification of a ‘balanced’ circulation is challenging wherein various parameters should be evaluated in close conjunction with each other. The prompt identification of circulatory maldistribution should be backed up with a sound management strategy aimed at attaining an equitable systemic and pulmonary perfusion. Any degree of ventricular dysfunction compromises the total output (Q_p + Q_s) supplying the two circuits explaining the role of inodilators in improving the myocardial performance in addition to lowering the systemic vascular resistance and optimizing Q_p/Q_s in setting of a single-ventricle physiology. Moreover, the pulmonary circulation is modulated by a multitude of factors intricately linked to the single-ventricle lesion, including anatomical characteristics unique to the underlying lesion (branch pulmonary arterial and venous stenosis), preoperative interventions, associated aortopulmonary and venovenous collaterals, plastic bronchitis, pulmonary arteriovenous fistulae, underlying ventricular dysfunction,, and many others. The article highlights the physiology, diagnosis, therapeutic optimization of a single-ventricle circulation, and the peculiarities pertaining to the pulmonary circulation of the uni-ventricular lesions.