Comparative outcome of bidirectional Glenn shunt in patients with pulmonary vascular resistance > or = 3.5 woods units versus < 3.5 woods units

Intraoperative Flow Study Predicted the Postoperative Pulmonary Artery Pressure in the Bidirectional Glenn Operation

Background:

The aim of this study was to evaluate the predictability of postoperative pulmonary artery pressure (PAP) using intraoperative flow study in patients undergoing bidirectional Glenn operation.

Methods:

Patients who underwent Glenn operation under cardiopulmonary bypass (CPB) were included in the study. During the operation, after the completion of additional procedures under CPB, an intraoperative flow study was performed prior to Glenn anastomosis. After the completion of bidirectional Glenn, the patient was separated from the CPB and PAP was measured. The relationship between this pressure and flow study measurement was analyzed.

Results:

Nine patients who underwent bidirectional Glenn operation with additional procedures under CPB between July 2018 and January 2019 were included in the study. The median PAP was 9 mm Hg (interquartile range [IQR]: 7-10 mm Hg) in the flow study and 10 mm Hg (IQR: 8-11 mm Hg) after CPB, and the median difference between these pressures was 1 mm Hg (IQR: 1-3 mm Hg). There was a strong correlation between these two measurements ( r = 0.732; P = .025).

Conclusion:

The results of this study show that PAP after the Glenn procedure can be estimated using an intraoperative flow study. We believe that this method may be useful in intraoperative decision-making for Glenn operation in single ventricular patients who require extensive pulmonary artery (PA) reconstruction due to limited PA development, branch PA stenosis, or nonconfluent PAs. Also, this method can be used as a sort of intraoperative pulmonary resistance reversibility study in patients with high preoperative pulmonary vascular resistance due to surgically correctable pulmonary venous hypertension.

Elevated Pulmonary Artery Pressure, Not Pulmonary Vascular Resistance, is an Independent Predictor of Short-Term Morbidity Following Bidirectional Cavopulmonary Connection

Single ventricle palliation relies on the pulmonary vasculature accommodating non-pulsatile systemic venous return. Mean pulmonary artery pressure (MPAP) and indexed pulmonary vascular resistance (PVRi) are two measures that impact pulmonary blood flow following bidirectional cavopulmonary connection (BCPC). The purpose of the study was to determine which hemodynamic features are associated with adverse outcomes after BCPC. Pre-operative hemodynamic data and post-operative morbidity and mortality in 250 patients undergoing BCPC at a single center from 2008 to 2014 were reviewed. Patients were then separated into 5 physiologic states based on MPAP, PVRi, and degree of pulmonary to systemic blood flow (Q_p:Q_s). There were 9 (3.6%) deaths, and 49 patients (20%) sustained major morbidity. An ROC curve identified MPAP > 16 mmHg as an inflection point. Pre-BCPC sildenafil and oxygen use, ventricular dysfunction, and MPAP > 16 mmHg (OR 4.1 [95% CI 1.8-9.2]) were independently associated with morbidity. MPAP > 16 mmHg (OR 6.7 [95% CI 1.6-28]) and pre-BCPC oxygen use were associated with hospital mortality. PVRi was not associated with morbidity or mortality. Of the five physiologic states, patients with high MPAP, low PVRi, and low Q_p:Q_s fared the worst, with the highest risk of major morbidity (OR 8.6 [3.0-24.9]) and highest risk of mortality (OR 8.0 [1.5-41.3]) when compared to their reference groups (low MPAP, low PVRi). Elevated MPAP, need for pre-operative oxygen support, sildenafil use, and systemic ventricular systolic dysfunction predict morbidity following BCPC. Specifically, patients with elevated MPAP not due to elevated PVRi or pulmonary blood flow had the highest risk of morbidity and mortality.

Understanding Stage II Bidirectional Cavopulmonary Shunts

Despite improvements in surgical technique and medical management, single-ventricle lesions remain one of the most challenging congenital heart anomalies to treat, and mortality rates are high. Most infants who have single-ventricle palliation undergo a sequence of surgeries to optimize pulmonary and systemic blood flow. The first surgery to separate pulmonary and systemic blood flow is the bidirectional cavopulmonary shunt. This article describes single-ventricle lesions and gives a basic overview of outcomes and strategies to improve interstage mortality. Preoperative investigations that evaluate stage II candidacy are reviewed along with surgical approaches and postoperative physiology. Although mortality rates are low and decreasing in patients with bidirectional cavopulmonary shunts, morbidity is still a challenge. Nurses must understand the pertinent anatomy and physiology and recognize postoperative complications early in order to reduce morbidity. Postoperative complications, management, outcomes and nursing care are discussed.

Exercise capacity in the Bidirectional Glenn physiology: Coupling cardiac index, ventricular function and oxygen extraction ratio

In Bi-directional Glenn (BDG) physiology, the superior systemic circulation and pulmonary circulation are in series. Consequently, only blood from the superior vena cava is oxygenated in the lungs. Oxygenated blood then travels to the ventricle where it is mixed with blood returning from the lower body. Therefore, incremental changes in oxygen extraction ratio (OER) could compromise exercise tolerance. In this study, the effect of exercise on the hemodynamic and ventricular performance of BDG physiology was investigated using clinical patient data as inputs for a lumped parameter model coupled with oxygenation equations. Changes in cardiac index, Qp/Qs, systemic pressure, oxygen extraction ratio and ventricular/vascular coupling ratio were calculated for three different exercise levels. The patient cohort (n=29) was sub-grouped by age and pulmonary vascular resistance (PVR) at rest. It was observed that the changes in exercise tolerance are significant in both comparisons, but most significant when sub-grouped by PVR at rest. Results showed that patients over 2 years old with high PVR are above or close to the upper tolerable limit of OER (0.32) at baseline. Patients with high PVR at rest had very poor exercise tolerance while patients with low PVR at rest could tolerate low exercise conditions. In general, ventricular function of SV patients is too poor to increase CI and fulfill exercise requirements. The presented mathematical model provides a framework to estimate the hemodynamic performance of BDG patients at different exercise levels according to patient specific data.

Effect of high altitude exposure on the hemodynamics of the bidirectional Glenn physiology: modeling incremented pulmonary vascular resistance and heart rate

The considerable blood mixing in the bidirectional Glenn (BDG) physiology further limits the capacity of the single working ventricle to pump enough oxygenated blood to the circulatory system. This condition is exacerbated under severe conditions such as physical activity or high altitude. In this study, the effect of high altitude exposure on hemodynamics and ventricular function of the BDG physiology is investigated. For this purpose, a mathematical approach based on a lumped parameter model was developed to model the BDG circulation. Catheterization data from 39 BDG patients at stabilized oxygen conditions was used to determine baseline flows and pressures for the model. The effect of high altitude exposure was modeled by increasing the pulmonary vascular resistance (PVR) and heart rate (HR) in increments up to 80% and 40%, respectively. The resulting differences in vascular flows, pressures and ventricular function parameters were analyzed. By simultaneously increasing PVR and HR, significant changes (p <0.05) were observed in cardiac index (11% increase at an 80% PVR and 40% HR increase) and pulmonary flow (26% decrease at an 80% PVR and 40% HR increase). Significant increase in mean systemic pressure (9%) was observed at 80% PVR (40% HR) increase. The results show that the poor ventricular function fails to overcome the increased preload and implied low oxygenation in BDG patients at higher altitudes, especially for those with high baseline PVRs. The presented mathematical model provides a framework to estimate the hemodynamic performance of BDG patients at different PVR increments.

Risk factors for prolonged length of stay after the stage 2 procedure in the single-ventricle reconstruction trial

BACKGROUND

The single-ventricle reconstruction trial randomized patients with single right ventricle lesions to a modified Blalock-Taussig or right ventricle-to-pulmonary artery shunt at the Norwood. This analysis describes outcomes at the stage 2 procedure and factors associated with a longer hospital length of stay (LOS).

METHODS

We examined the association of shunt type with stage 2 hospital outcomes. Cox regression and bootstrapping were used to evaluate risk factors for longer LOS. We also examined characteristics associated with in-hospital death.

RESULTS

There were 393 subjects in the analytic cohort. Median stage 2 procedure hospital LOS (8 days; interquartile range [IQR], 6-14 days), hospital mortality (4.3%), transplantation (0.8%), median ventilator time (2 days; IQR, 1-3 days), median intensive care unit LOS (4 days; IQR, 3-7 days), number of additional cardiac procedures or complications, and serious adverse events did not differ by shunt type. Longer LOS was associated (R(2) = 0.26) with center, longer post-Norwood LOS (hazard ratio [HR], 1.93 per log day; P < .001), nonelective timing of the stage 2 procedure (HR, 1.78; P < .001), and pulmonary artery (PA) stenosis (HR, 1.56; P < .001). By univariate analysis, nonelective stage 2 (65% vs 32%; P = .009), moderate or greater atrioventricular valve (AVV) regurgitation (75% vs 24%; P < .001), and AVV repair (53% vs 9%; P < .001) were among the risk factors associated with in-hospital death.

CONCLUSIONS

Norwood LOS, PA stenoses, and nonelective stage 2 procedure, but not shunt type, are independently associated with longer LOS. Nonelective stage 2 procedure, moderate or greater AVV regurgitation, and need for AVV repair are among the risk factors for death.

Preoperative pulmonary hemodynamics and assessment of operability: is there a pulmonary vascular resistance that precludes cardiac operation?

Preoperative pulmonary vascular disease remains an important risk factor for death or right-heart failure in selected children undergoing two-ventricle repair, single-ventricle palliation, or heart transplantation. Preoperative criteria for poor outcome after operation remain unclear. The purpose of this review is to critically assess both the historic and current data and make recommendations where appropriate. An extensive literature search was undertaken in October 2009. Data were analyzed by an expert multidisciplinary team and recommendations were made by consensus. PubMed was searched in October 2009. Data were analyzed and recommendations were made by consensus of a multidisciplinary team. In patients with suspected pulmonary vascular disease anticipating a two-ventricle repair, although preoperative testing via cardiac catheterization with vasodilators is reasonable, the preoperative parameters and the precise values of these parameters that best correlate with early and late outcome remain unclear. Further investigation is warranted in selected populations, such as the growing group of children with congenital heart disease complicated by chronic lung disease of prematurity, and in the developing world where patients may be more likely to present late with advanced pulmonary vascular disease. In patients with a functional single ventricle, there is growing evidence that mean pulmonary artery pressure of >15 mm Hg may be associated with both early and late mortality after the Fontan operation. The relationship of preoperative pulmonary hemodynamics to early and late morbidity remains to be defined. There most likely is a level of preoperative pulmonary vascular disease that puts an individual patient at increased risk for death or severe cyanosis after a bidirectional cavopulmonary anastomosis. It remains unclear, however, how to best assess this risk preoperatively. The limitations in obtaining an accurate assessment of pulmonary vascular disease in the complex single ventricle are discussed. In children awaiting cardiac transplantation with elevated pulmonary vascular disease of >6 U.m and/or transpulmonary gradient of >15 mm Hg, heart transplantation is deemed feasible in most transplant centers if the administration of inotropes or vasodilators can decrease the pulmonary vascular disease to <6 U.m or transpulmonary gradient to <15 mm Hg. In patients with preoperative pulmonary vascular disease, there may be contributing factors to the pulmonary vascular disease, such as the specifics of the cardiac lesion (atrioventricular valve regurgitation, low cardiac output), parenchymal and/or airway issues, and/or individual genetic predisposition. Amelioration of any reversible factors before operation and optimization of their management in the preoperative and postoperative period are recommended.