Triston Smith

Considerations for numerical modeling of the pulmonary circulation--a review with a focus on pulmonary hypertension.

Both in academic research and in clinical settings, virtual simulation of the cardiovascular system can be used to rapidly assess complex multivariable interactions between blood vessels, blood flow, and the heart. Moreover, metrics that can only be predicted with computational simulations (e.g., mechanical wall stress, oscillatory shear index, etc.) can be used to assess disease progression, for presurgical planning, and for interventional outcomes. Because the pulmonary vasculature is susceptible to a wide range of pathologies that directly impact and are affected by the hemodynamics (e.g., pulmonary hypertension), the ability to develop numerical models of pulmonary blood flow can be invaluable to the clinical scientist. Pulmonary hypertension is a devastating disease that can directly benefit from computational hemodynamics when used for diagnosis and basic research. In the present work, we provide a clinical overview of pulmonary hypertension with a focus on the hemodynamics, current treatments, and their limitations. Even with a rich history in computational modeling of the human circulation, hemodynamics in the pulmonary vasculature remains largely unexplored. Thus, we review the tasks involved in developing a computational model of pulmonary blood flow, namely vasculature reconstruction, meshing, and boundary conditions. We also address how inconsistencies between models can result in drastically different flow solutions and suggest avenues for future research opportunities. In its current state, the interpretation of this modeling technology can be subjective in a research environment and impractical for clinical practice. Therefore, considerations must be taken into account to make modeling reliable and reproducible in a laboratory setting and amenable to the vascular clinic. Finally, we discuss relevant existing models and how they have been used to gain insight into cardiopulmonary physiology and pathology.

Patient-specific computational modeling of blood flow in the pulmonary arterial circulation

Computational fluid dynamics (CFD) modeling of the pulmonary vasculature has the potential to reveal continuum metrics associated with the hemodynamic stress acting on the vascular endothelium. It is widely accepted that the endothelium responds to flow-induced stress by releasing vasoactive substances that can dilate and constrict blood vessels locally. The objectives of this study are to examine the extent of patient specificity required to obtain a significant association of CFD output metrics and clinical measures in models of the pulmonary arterial circulation, and to evaluate the potential correlation of wall shear stress (WSS) with established metrics indicative of right ventricular (RV) afterload in pulmonary hypertension (PH). Right Heart Catheterization (RHC) hemodynamic data and contrast-enhanced computed tomography (CT) imaging were retrospectively acquired for 10 PH patients and processed to simulate blood flow in the pulmonary arteries. While conducting CFD modeling of the reconstructed patient-specific vasculatures, we experimented with three different outflow boundary conditions to investigate the potential for using computationally derived spatially averaged wall shear stress (SAWSS) as a metric of RV afterload. SAWSS was correlated with both pulmonary vascular resistance (PVR) (R(2)=0.77, P<0.05) and arterial compliance (C) (R(2)=0.63, P<0.05), but the extent of the correlation was affected by the degree of patient specificity incorporated in the fluid flow boundary conditions. We found that decreasing the distal PVR alters the flow distribution and changes the local velocity profile in the distal vessels, thereby increasing the local WSS. Nevertheless, implementing generic outflow boundary conditions still resulted in statistically significant SAWSS correlations with respect to both metrics of RV afterload, suggesting that the CFD model could be executed without the need for complex outflow boundary conditions that require invasively obtained patient-specific data. A preliminary study investigating the relationship between outlet diameter and flow distribution in the pulmonary tree offers a potential computationally inexpensive alternative to pressure based outflow boundary conditions.

Acute Myocardial Infarction Associated with Dietary Supplements Containing 1,3-Dimethylamylamine and Citrus aurantium

We describe the case of a previously healthy 22-year-old man who presented with anginal chest pain and was diagnosed with a non-ST-elevation myocardial infarction. For 3 weeks, he had been ingesting the dietary supplements Jack3d® (principal ingredient, 1,3-dimethylamylamine) and Phenorex™ (principal ingredient, Citrus aurantium) daily, before undertaking physical activity. Coronary angiograms revealed a proximal left anterior descending coronary artery thrombus with distal embolization. A combined medical regimen led to resolution of the thrombus. Three months later, the patient was asymptomatic with no evidence of ischemia. The primary ingredients in the sympathomimetic supplements taken by our patient are controversial in the medical community and have been individually associated with adverse cardiac events. There are no safety data on their simultaneous use. We discuss other reports of adverse effects associated with these supplements and recommend that the relevant safety guidelines be revised.

The role of wall shear stress in the assessment of right ventricle hydraulic workload.

Pulmonary hypertension (PH) is a devastating disease affecting approximately 15–50 people per million, with a higher incidence in women. PH mortality is mostly attributed to right ventricle (RV) failure, which results from RV hypotrophy due to an overburdened hydraulic workload. The objective of this study is to correlate wall shear stress (WSS) with hemodynamic metrics that are generally accepted as clinical indicators of RV workload and are well correlated with disease outcome. Retrospective right heart catheterization data for 20 PH patients were analyzed to derive pulmonary vascular resistance (PVR), arterial compliance (C), and an index of wave reflections (Γ). Patient-specific contrast-enhanced computed tomography chest images were used to reconstruct the individual pulmonary arterial trees up to the seventh generation. Computational fluid dynamics analyses simulating blood flow at peak systole were conducted for each vascular model to calculate WSS distributions on the endothelial surface of the pulmonary arteries. WSS was found to be decreased proportionally with elevated PVR and reduced C. Spatially averaged WSS (SAWSS) was positively correlated with PVR (R 2 = 0.66), C (R 2 = 0.73), and Γ (R 2 = 0.5) and also showed promising preliminary correlations with RV geometric characteristics. Evaluating WSS at random cross sections in the proximal vasculature (main, right, and left pulmonary arteries), the type of data that can be acquired from phase-contrast magnetic resonance imaging, did not reveal the same correlations. In conclusion, we found that WSS has the potential to be a viable and clinically useful noninvasive metric of PH disease progression and RV health. Future work should be focused on evaluating whether SAWSS has prognostic value in the management of PH and whether it can be used as a rapid reactivity assessment tool, which would aid in selection of appropriate therapies.

An unusual etiology of infective endocarditis: Enterobacter cloacae

Gram-negative microorganisms are rarely implicated in causing infective endocarditis (IE). Although the traditionally identified risk factor for Gram-negative endocarditis has been intravenous drug abuse, recent studies have revealed that healthcare contact and the presence of prosthetic cardiac devices are primary risk factors for IE secondary to non-HACEK Gram-negative bacteria. We present a case of Enterobacter endocarditis in a patient with no prior history of valvular heart disease, implanted endovascular device, or intravenous drug abuse. The patient was treated successfully with carbapenem monotherapy. We have reviewed 43 cases of Enterobacter endocarditis reported in the literature to date. Clinical summary and management of IE secondary to Enterobacter based on all the published cases is outlined.

Prolonged duration of transbrachial intra-aortic balloon pump as bridge to heart transplantation

We describe a case demonstrating the quality of life (QOL) benefit and safety of using a transbrachial approach for insertion of an intra-aortic balloon pump (IABP) in a patient awaiting cardiac transplantation. A 68-year-old man with ischaemic cardiomyopathy was admitted to our cardiac intensive care unit to await the availability of a suitable donor organ for orthotopic heart transplant. An IABP was needed for haemodynamic support due to cardiogenic shock. Since the patient did not want to be committed to lying supine in bed for multiple days, as would have been the case had the IABP been placed using the conventional femoral route, we inserted a 7.5 Fr ‘sheathless’ IABP via the transbrachial approach. The patients haemodynamics improved and the device was left in place for 240 h without vascular compromise. He was subsequently successfully transplanted and is doing well on follow-up.

Exclusion of Giant Coronary Artery Aneurysm with Covered Stent Combinedwith Coil Embolization of Vessel Outflow

Background: Coronary artery aneurysms (CAA) are rare abnormal dilatation of the coronary arteries. They are termed giant if their diameter exceeds the reference vessel diameter by more than 4 times or if they are more than 8 mm in diameter. If not treated, they have a tendency to rupture, thrombose or embolize. There is however no definite therapy for CAA. Various therapies suggested in the management of aneurysms include surgical resection, covered stent implantation or coil embolization. Methods: We describe a case of coiling of a potential collateral vessel feeding the giant coronary aneurysm retrogradely and covered stenting of main branch to exclude the aneurysm. Results: Transcatheter embolization was successfully done. No late complications were seen during 1 year CT angiography. Conclusion: Dual stent and coil embolization is safe and effective for vessel outflow during the treatment of giant coronary artery aneurysm. Further long term outcomes will have to be determined through serial CT angiographies.

Type I Kounis syndrome variant: A case report and literature review

Kounis syndrome defined as the occurrence of acute coronary syndrome in the setting of allergic reaction due to mast cells activation and inflammatory mediators release that induces coronary vasospasm, plaque erosion, or even stent thrombosis. A 25-year-old postpartum female with asthma and recurrent episodes of chest pain was admitted with ST-segment elevation myocardial infarction in the setting of coronary artery spasms. The patient was started on calcium channel blockers and nitrite-based medication with no improvement. She was noted to have eosinophilia and initiation of corticosteroid-based regimen lead to resolution of chest pain episodes and normalization of eosinophilia. Kounis syndrome should be considered in young patients with chest pain. Coronary vasodilators are considered as the first-line of treatment. The use of corticosteroids has been described in the literature in severe or refractory cases.

THE EFFECT OF OBSTRUCTIVE SLEEP APNEA ON IN-HOSPITAL MORTALITY IN PATIENTS WITH ACUTE PULMONARY EMBOLISM

Obstructive sleep apnea (OSA) and pulmonary emboli (PE) have both been independently associated with increased mortality. While acute PE can frequently lead to catastrophic short-term outcomes, its concomitant effect with OSA on mortality has not been clearly identified. We hypothesized that

The influence of pulmonary hemodynamics on right ventricular function in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a degenerative disease that can lead to substantial morphometric remodeling of the pulmonary arteries. Previous studies have revealed coupling relationships between right ventricular (RV) function and pulmonary arterial hemodynamics. The objective of this study was to utilize computational fluid dynamics (CFD) to estimate spatially averaged Wall Shear Stress (WSS) for patients with PH and explore correlations between hemodynamics metrics and RV function.© 2013 ASME