Contributions of Respiration and Heartbeat to the Pulmonary Blood Flow in the Fontan Circulation

A porcine model of postoperative hemi-diaphragmatic paresis to evaluate a unilateral diaphragmatic pacemaker

Unilateral phrenic nerve damage is a dreaded complication in congenital heart surgery. It has deleterious effects in neonates and children with uni-ventricular circulation. Diaphragmatic palsy, caused by phrenic nerve damage, impairs respiratory function, especially in new-borns, because their respiration depends on diaphragmatic contractions. Furthermore, Fontan patients with passive pulmonary perfusion are seriously affected by phrenic nerve injury, because diaphragmatic contraction augments pulmonary blood flow. Diaphragmatic plication is currently employed to ameliorate the negative effects of diaphragmatic palsy on pulmonary perfusion and respiratory mechanics. This procedure attenuates pulmonary compression by the abdominal contents. However, there is no contraction of the plicated diaphragm and consequently no contribution to the pulmonary blood flow. Hence, we developed a porcine model of unilateral diaphragmatic palsy in order to evaluate a diaphragmatic pacemaker. Our illustrated step-by-step description of the model generation enables others to replicate and use our model for future studies. Thereby, it might contribute to investigation and advancement of potential improvements for these patients.

Assessing Single Ventricle Function in the Fontan Circulation using Wave Intensity Analysis

Single ventricle hearts palliated with the Fontan operation present complications later in life as a result of increased venous pressures and abnormal ventricle function. Wave intensity analysis uses measurements of blood velocity and pressure to represent arterial hemodynamics as summations of energy waves. This methodology could potentially be a useful tool in assessment of Fontan patients. The clinical value of wave intensity parameters was utilized to evaluate the functional performance of the single ventricle in Fontan patients. A retrospective analysis of invasive hemodynamic data was retrospectively obtained from routine cardiac catheterization of patients with Fontan circulation (n = 20) and comparison to those with biventricular circulation (n = 10) who presented to the catheterization laboratory for closure of small patent ductus arteriosus (PDAs). Wave intensity analysis and wave energy flux was calculated using aortic pressure waveforms and echocardiography aortic Doppler measurements as previously described. Significant differences were seen in the peak forward compression wave (p = 0.013), early systolic energy flux (p = 0.005) and the systolic and diastolic ratio (p = 0.006) in Fontan patients versus controls. Within the Fontan group, there was a positive correlation (0.54, p = 0.02) between the wave speed and pulmonary vascular resistance. Early systolic energy flux was a potential individual indicator of a Fontan patients heart failure classification (AUC = 0.71). Wave intensity analysis could be a useful tool in screening Fontan patients and predicting clinical outcomes and Fontan failure. Future prospective analyses of Fontan hemodynamics and WIA are needed.

Computational fluid dynamics simulations of flow distribution and graft designs in apicoaortic bypass

OBJECTIVE

Apicoaortic bypass has double outlets and its graft design is similar to that of a left ventricular assist device (LVAD). The left ventricular apex to the descending aorta (LV-DsAo) bypass is widely used in apicoaortic bypass. In contrast, the left ventricular apex to the ascending aorta (LV-AsAo) bypass is standard in LVAD surgery. This study aimed to evaluate the graft designs of apicoaortic bypass and their effects on flow distribution and energy loss (EL).

METHODS

A simulation study using computational fluid dynamics was performed on the geometry and hemodynamics data obtained from a 30-year-old patient who underwent a LV-DsAo bypass. The ratio of the cardiac output (CO) through the ascending aorta (AsAo) and apicoaortic conduit was set at 50:50, 30:70, and 10:90. Regional blood flow (RBF) and EL were calculated for the different distribution ratios. As an alternative to the LV-DsAo bypass, a virtual LV-AsAo bypass surgery was performed, and each parameter was compared with that of the LV-DsAo bypass.

RESULTS

At a distribution ratio of 50:50, the RBF to the head and EL were 16.4% of the total CO and 62.0 mW in the LV-DsAo bypass, and 32.3% and 81.5 mW in the LV-AsAo bypass, respectively. The RBF to the head decreased with the CO through the AsAo in the LV-DsAo bypass, but it was constant in the LV-AsAo bypass. The EL increased inversely with the CO through the AsAo in both graft designs.

CONCLUSION

The regional blood flow distribution was different, but the trend of the EL which increased inversely with the CO through the AsAo was similar between the LV-DsAo and LV-AsAo bypasses.

Flow profile characteristics in Fontan circulation are associated with the single ventricle dilation and function: principal component analysis study

The Fontan circulation is characterized as a nonpulsatile flow propagation without a pressure-generating ventricle. However, flow through the Fontan circulation still exhibits oscillatory waves as a result of pressure changes generated by the systemic single ventricle. Identification of discrete flow patterns through the Fontan circuit may be important to understand single ventricle performance. Ninety-seven patients with Fontan circulation underwent phase-contrast MRI of the right pulmonary artery, yielding subject-specific flow waveforms. Principal component (PC) analysis was performed on preprocessed flow waveforms. Principal components were then correlated with standard MRI indices of function, volume, and aortopulmonary collateral flow. The first principal component (PC) described systolic versus diastolic-dominant flow through the Fontan circulation, accounting for 31.3% of the variance in all waveforms. The first PC correlated with end-diastolic volume (R = 0.34, P = 0.001), and end-systolic volume (R = 0.30, P = 0.003), cardiac index (R = 0.51, P < 0.001), and the amount of aortopulmonary collateral flow (R = 0.25, P = 0.027)-lower ventricular volumes and a smaller volume of collateral flow-were associated with diastolic-dominant cavopulmonary flow. The second PC accounted for 19.5% of variance and described late diastolic acceleration versus deceleration and correlated with ejection fraction-diastolic deceleration was associated with higher ejection fraction. Principal components describing the diastolic flow variations in pulmonary arteries are related to the single ventricle function and volumes. Particularly, diastolic-dominant flow without late acceleration appears to be related to preserved ventricular volume and function, respectively.NEW & NOTEWORTHY The exact physiological significance of flow oscillations of phasic and temporal flow variations in Fontan circulation is unknown. With the use of principal component analysis, we discovered that flow variations in the right pulmonary artery of Fontan patients are related to the single ventricle function and volumes. Particularly, diastolic-dominant flow without late acceleration appears to be related to more ideal ventricular volume and systolic function, respectively.

Scoliosis Correction with One Ventricle: A Multispecialty Approach

BACKGROUND

Patients with single-ventricle congenital heart disease may present for scoliosis correction. These patients undergo a series of cardiac operations that create a novel circulation that has a significant impact on the management of their spinal surgery.

CASE DESCRIPTION

A 21-year-old man with severe scoliosis presented for posterior T4-L3 spinal fusion. He was born with complex congenital heart disease that resulted in his having a single functioning ventricle. He underwent a series of operations culminating in a Fontan procedure to palliate his heart disease. Both the surgical procedure and the anesthetic plan were modified based on his abnormal physiology, which led to a successful correction with no complications.

CONCLUSIONS

Patients who have undergone a Fontan procedure can successfully undergo a lengthy scoliosis correction, but it requires multidisciplinary planning.

Respiration Dependency of Caval Blood Flow in Patients with Fontan Circulation: Quantification Using 5D Flow MRI

PURPOSE

To measure respiration-dependent blood flow in the total cavopulmonary connection (TCPC) of patients with Fontan circulation by using free-running, fully self-gated five-dimensional (5D) flow MRI.

MATERIALS AND METHODS

From July to November 2018, 10 volunteers (six female volunteers, mean age, 25.1 years ± 4.4 [standard deviation]) and six patients with Fontan circulation (two female patients, mean age, 19.7 years ± 7.5) with a TCPC were examined by using a cardiac- and respiration-resolved three-directional and three-dimensional phase-contrast MRI sequence (hereafter, 5D flow MRI). This prospective study was conducted with approval of the local ethics committee, and written informed consent was obtained from all participants and/or their representative. 5D flow data were acquired during free breathing. Data were reconstructed into 15-20 heart phases and four respiratory phases: end-expiration, inspiration, end-inspiration, and expiration. Respiration-dependent stroke volumes (SVs) and particle traces were analyzed from the caval circulation of volunteers and patients with Fontan circulation. Statistical analysis was performed by using parametric tests and scatterplots.

RESULTS

The respiration dependency of caval blood flow was evaluated in all participants and was significantly elevated in patients with Fontan circulation as compared with volunteers. In patients, SV in the inferior vena cava (IVC) showed variations of 120% between inspiration and expiration (P = .002). The flow distribution in the IVC and superior vena cava among the four respiratory phases was differentiated by 20% (range, 9%-30%) and 4% (range, 0%-13%), respectively.

CONCLUSION

Hemodynamic parameters (volume flow and blood flow distribution) throughout the cardiac and respiratory cycle can be measured using a single scan, potentially providing further insights into the Fontan circulation.© RSNA, 2019Supplemental material is available for this article.

Extubation in the Operating Room After Fontan Procedure: Does It Make a Difference?

Early extubation appears to have beneficial effects on the Fontan circulation. The goal of this study was to assess the impact of extubation on the operating table in comparison with extubation during the first hours after Fontan operation (FO) on the early postoperative course. Between 2013 and 2016, 114 children with a single ventricle heart malformations (mean age, 3.8 ± 2.3 years) underwent FO: 60 patients were extubated in the operating room (ORE) and 54 in the intensive care unit (ICUE) in the median time of 195 min (range 30-515 min) after procedure. Pre-, peri-, and postoperative records were retrospectively analyzed. The hospital survival rate was 100%. One patient from the ORE group needed an immediate reintubation because of laryngospasm. The ORE group showed lower heart rate (106.5 vs. 120.3 bpm; p < 0.001) and lower central venous pressure (10.4 vs. 11.4 mmHg; p = 0.001) than patients in the ICUE group within the first 24 h after FO, as well as higher systolic blood pressure within 7 h after operation (88.6 ± 2.5 vs. 85.6 ± 2.6 mmHg; p = 0.036). The ORE children manifested significantly less pleural effusions during 48 h after FO (38.0 vs. 49.5 ml/kg; p = 0.004), received less intravenous fluid administration within 24 h after FO (54.1 vs. 73.8 ml/kg; p = 0.019), less inotropic support (9.8 vs. 12.8 h of dopamine; p = 0.033), and less antibiotics (4.7 vs. 5.8 days; p = 0.037). ICUE children manifested metabolic acidosis more frequently than the ORE group 3-4 h after FO (p < 0.05). Immediate extubation after FO in comparison with extubation in the ICU appears to be associated with improved hemodynamics and reduced application of therapeutic interventions in the postoperative course.

Efficacy of Sports Club Activities on Exercise Tolerance Among Japanese Middle and High School Children and Adolescents After Fontan Procedure

The exercise tolerance of Fontan patients is poorer than that of healthy people. Some previous studies reported that exercise tolerance can be improved in this population by cardiac rehabilitation. This study aimed to determine the factors associated with peak oxygen uptake (VO2) and to subsequently clarify the correlation between participation in sports club activities and variables related to exercise tolerance. Cardiopulmonary exercise tests were performed by 115 Fontan patients aged between 6 and 20 years. The patients completed questionnaires on their daily physical activities including participation in extracurricular sports clubs in middle (junior high school) and high school. Peak VO2 had a significant negative correlation with age and a positive correlation with hemoglobin, stroke volume, and resting tidal volume in the entire study group. Additionally, the sports club participants who were middle and high school students had significantly higher peak VO2 and resting tidal volume. Exercise habits including participation in sports club activities may promote exercise tolerance by improving respiratory function in Fontan adolescents.

New imaging tools in cardiovascular medicine: computational fluid dynamics and 4D flow MRI

Blood flow imaging is a novel technology in cardiovascular medicine and surgery. Today, two types of blood flow imaging tools are available: measurement-based flow visualization including 4D flow MRI (or 3D cine phase-contrast magnetic resonance imaging), or echocardiography flow visualization software, and computer flow simulation modeling based on computational fluid dynamics (CFD). MRI and echocardiography flow visualization provide measured blood flow but have limitations in temporal and spatial resolution, whereas CFD flow calculates the flow according to assumptions instead of flow measurement, and it has sufficiently fine resolution up to the computer memory limit, and it enables even virtual surgery when combined with computer graphics. Blood flow imaging provides profound insight into the pathophysiology of cardiovascular diseases, because it quantifies and visualizes mechanical stress on the vessel walls or heart ventricle. Wall shear stress (WSS) is a stress on the endothelial wall caused by the near wall blood flow, and it is thought to be a predictor of atherosclerosis progression in coronary or aortic diseases. Flow energy loss (EL) is the loss of blood flow energy caused by viscous friction of turbulent diseased flow, and it is expected to be a predictor of ventricular workload on various heart diseases including heart valve disease, cardiomyopathy, and congenital heart diseases. Blood flow imaging can provide useful information for developing predictive medicine in cardiovascular diseases, and may lead to breakthroughs in cardiovascular surgery, especially in the decision-making process.