Fig. 38.1
Schematic view of UVAD placement in single ventricle anatomy after first-stage palliation (Norwood with modified BT shunt) of HLHS. The inflow cannula is inserted in the apex of the single right ventricle and the outflow cannula at the level of the Damus-Kaye-Stansel anastomosis, leaving the shunt open to allow the pulmonary circulation. UVAD univentricular assist device, HLHS hypoplastic left heart syndrome
Fig. 38.2
Schematic view of UVAD placement in single ventricle anatomy after second-stage palliation (Glenn circulation) of HLHS. The inflow cannula is inserted in the apex of the single right ventricle and the outflow cannula at the level of the Damus-Kaye-Stansel anastomosis. UVAD univentricular assist device, HLHS hypoplastic left heart syndrome
A biventricular VAD (BiVAD) configuration can also be used using BH EXCOR for HLHS as shown in ◘ Fig. 38.3. The fundamental requirement is to create a systemic venous reservoir by joining the superior vena cava to the right atrium and thereafter separating the systemic venous from the pulmonary venous drainage. The left-sided VAD is implanted as described above, and the right-sided VAD is inserted with inflow cannula in the new artificial systemic venous atrium and the outflow cannula in the right pulmonary artery. The systemic to pulmonary shunt is finally ligated or disconnected.
Fig. 38.3
Schematic view of BiVAD placement in single ventricle anatomy after first-stage palliation (Norwood with modified BT shunt) of HLHS. The physiology is converted to a biventricular circulation dividing the systemic venous return from the pulmonary venous return. BiVAD biventricular assist device, HLHS hypoplastic left heart syndrome
Additional pulmonary artery obstruction, intracardiac shunts, and both atrioventricular and semilunar valve incompetence must be addressed and repaired at time of VAD implantation.
Patients with failing single ventricle are likely to have multiorgan dysfunction before VAD implantation with minimal response to medical treatment and hemodynamic instability with signs of end-organ dysfunction [1–6]. Invasive ventilation and ECMO support are required in nearly 50% of the cases prior to VAD insertion, respiratory failure being the commonest cause of death on MCS. Veno-venous and aortopulmonary collaterals that cause high pulmonary vascular resistance (PVR) must be closed in the first instance to avoid both chronic lung disease and systemic venous hypertension. Pre-existing renal and liver dysfunction is also associated with poor prognosis. Complications related to excessive bleeding are likely to be encountered in these patients and are due to a combination of multiple previous operations and coagulation abnormalities related to multisystem failure.
A palliated HLHS fails due to ventricular dysfunction, elevated pulmonary resistance, or a combination thereof [1, 3]. Horne and colleagues from Edmonton, Canada, rationalized an approach to VAD decision in univentricular circulation based on mechanisms of failure and patient weight (◘ Fig. 38.4). In the setting of primary ventricular dysfunction and normal PVR, standard UVAD may be adequate. A higher flow is required to cope with the increased load of the systemic single ventricle so that, equal to patient’s body surface area, a larger BH size pump is often required in shunt and Glenn physiology compared to the predicted left VAD size pump in biventricular circulation [2]. Instead, the presence of high PVR, high-end diastolic pressure, or mixed pathophysiological mechanisms may require the addition of a right-sided VAD (“pushing” pump) to adequately push blood in the pulmonary circulation.
Fig. 38.4
Approach to device decision in the univentricular heart based on patient weight and mechanism of failure. CO cardiac output, EDP end-diastolic pressure, PVR pulmonary vascular resistance, CVP central venous pressure, EXCOR Berlin heart EXCOR, VAD ventricular assist device, TAH total artificial heart
When the single ventricle physiology fails at the early stages of the palliation, the small size of the patients (most likely less than 15 kg) limits the VAD option to paracorporeal devices, with BH EXCOR and Levitronix (Thoratec Corporation, Pleasanton, CA) pumps providing pulsatile and continuous flow, respectively (◘ Fig. 38.4). The initial connection of CentriMag pump to the BH EXCOR cannulas is strongly recommended in case of transition from ECMO support, allowing the option of adding an oxygenator in the VAD circuit in case of persistent poor lung function [1–4]. In the acute phase, continuous flow is preferable as it can also allow a better unloading of the systemic ventricle, can occur throughout the entire cardiac cycle, and can consequently provide higher flow than pulsatile pumps at the same filling pressure [1, 3–5]. Furthermore, it can reduce pulmonary venous congestion avoiding pulmonary vein blood flow reversal that occurs with a pulsatile device in the absence of a compliant pulmonary venous atrium [1]. Finally, the anticoagulation management results easier in the setting of continuous VAD flow reducing the thromboembolic risk associated with BH EXCOR.
Two large series worldwide, a single institution experience from Newcastle upon Tyne, UK [2], and a multicenter study from the USA [4], demonstrated the feasibility of bridge to transplantation MCS in single ventricle physiology, using the combination of BH EXCOR, Levitronix, and ECMO. However, the success is limited compared to the congenital biventricular pediatric MCS population, with decreased overall survival to transplantation or VAD explantation. The complex anatomical and physiological nature of single ventricle in infants still remains a challenging proposition. In fact it could be argued that patients undergoing successful transplantation in these cohorts were lucky to have received a donor organ in a relatively short period of time, with none of the survivors mechanically assisted for longer than 21 days. Cerebrovascular events, bleeding, infective and multiorgan failure complications [2, 4, 6], and requirement of ECMO-type circulation post-VAD implantation due to persisent respiratory dysfunction are harbingers of adverse prognostic factors for death during MCS [2].
38.3 VAD for Fontan Failure
The interplay of various cardiovascular factors leading to failure of Fontan circulation is highlighted in ◘ Fig. 38.5 [7]. The Fontan failure is either due to ventricular dysfunction or as a consequence of failure of the Fontan circulation with preserved ventricular function. The principle of management of Fontan failure is to prolong the state of Fontan circulation and make these patients better candidates for heart transplantation. A wide variety of medical, catheter-based, or surgical intervention including MCS (◘ Fig. 38.6) represents the wide spectrum of tools at our disposal to achieve this.
Fig. 38.5
Cardiovascular system components and alterations in failing Fontan circulation. UV univentricular, BV biventricular, LV left ventricle, RV right ventricle, TCPC total cavopulmonary connection, HLHS hypoplastic left heart syndrome, PA pulmonary artery (Reprinted with permission of De Rita et al. [7])
Fig. 38.6
Represents the wide spectrum of tools at our disposal to achieve this (Reprinted with permission of De Rita et al. [7])
As general presumption, the identification of predominant etiology of failure may direct the most suitable approach to mechanically support the circulation (◘ Fig. 38.4). A standard “pulling” left-sided UVAD with ventricle to aorta connection may be adequate to unload the systemic single ventricle and decrease Fontan pressure in case of isolated or combined systolic and diastolic dysfunction [1, 3, 8, 9]. When the elevated systemic venous pressure is mainly a consequence of unusually isolated high PVR without evident pump failure, a single “pushing” right-sided system can be established to support only the pulmonary circulation, with surgical construction of a new venous reservoir joining the venae cavae to allow VAD filling and restitution of blood to the pulmonary arteries via the disconnected Fontan conduit (◘ Fig. 38.7) [10]. The BiVAD configuration is instead reasonable in case of the mixed mechanism of failure where the use of a single “pushing” UVAD might cause pulmonary congestion if a “pulling” system is not used in combination [11].
