Richard Warwick

Ascending aortic curvature as an independent risk factor for type a dissection, and ascending aortic aneurysm formation: a mathematical model

OBJECTIVEnTo develop a mathematical model to demonstrate that ascending aortic curvature is an independent risk factor for type A dissections, in addition to hypertension, bicuspid aortic valve, aneurysm of ascending aorta, and intrinsic aortic tissue abnormalities, like Marfans syndrome.nnnMETHODSnA steady state one-dimensional flow analysis was performed, utilising Newtons third law of motion. Five different clinical scenarios were evaluated: (1) effect of aortic curvature; (2) effect of beta-blockers, (3) effect of patient size, (4) forces on a Marfans aorta, and (5) site of entry flap in aortic dissection.nnnRESULTSnAortic curvature increases the forces exerted on the ascending aorta by a factor of over 10-fold. Aortic curvature can cause patients with a systolic blood pressure of 8 0mmHg to have greater forces exerted on their aorta despite smaller diameters and lower cardiac outputs, than patients with systolic blood pressures of 120 mmHg. In normal diameter aortas, beta-blockers have minimal effect compared with aortic curvature. Aortic curvature may help to explain why normal diameter aortas can dissect, and also that the point of the entry tear may be potentially predictable. Aortic curvature has major effects on the forces exerted on the aorta in patients with Marfans syndrome.nnnCONCLUSIONSnAortic curvature is relatively more important that aortic diameter, blood pressure, cardiac output, beta-blocker use, and patient size with regard to the force acting on the aortic wall. This may explain why some patients with normal diameter ascending aortas with or without Marfans syndrome develop type A dissections and aneurysms. Aortic curvature may also help to explain the site of entry tear in acute type A dissection. Further clinical study is needed to validate this studys finding.

The concept of aortic replacement based on computational fluid dynamic analysis: patient-directed aortic replacement

OBJECTIVESnAortic replacement is based on the aortic diameter in the absence of dissection or connective tissue diseases. Frequently, a number of different aortic-to-prosthetic anastomotic positions are possible depending on patient factors and surgeon preferences. High stress on residual aortic tissue may result in aneurysm formation or aneurysmal dilatation. Utilizing a computational fluid dynamic evaluation, we aimed to define possible optimal operative interventions with regard to the extent of aortic replacement.nnnMETHODSnFor proof of principle, a computational fluid dynamic (CFD) analysis, using Fluent 6.2 (Ansys UK Ltd, Sheffield, UK), was performed on a simplified ascending arch and descending aortic geometry. Wall shear stress in three dimensions was assessed for the standard operations: ascending aortic replacement, arch replacement and proximal descending aortic replacement.nnnRESULTSnHermiarch replacement is superior to isolated ascending aortic replacement with regard to residual stress analysis on tissues (up to a 10-fold reduction). Aortic arch replacement with island implantation of the supra-aortic vessels may potentially result in high stress on the residual aorta (10-fold increase). Aortic arch replacement with individual supra-aortic vessel implantation may result in areas of high stress (10-fold increase) on native vessels if an inadequate length of supra-aortic tissue is not resected, regardless of it being aneurysmal.nnnCONCLUSIONSnComputational fluid dynamic evaluation, which will have to be patient-specific, 3D anatomical and physiological, potentially has enormous implications for operative strategy in aortic replacement surgery. CFD analysis may direct the replacement of normal-diameter aortas in the future.

Mathematical modelling to identify patients who should not undergo left ventricle remodelling surgery

A mathematical model was developed to predict the cardiac output post left ventricle volume reduction surgery (LVVRS) to establish who should not undergo surgery. Two scenarios were evaluated: dilated cardiomyopathy (DCM), and left ventricular wall aneurysm (LVA). In DCM, a left ventricular diastolic volume (LVDV) of 380 ml, ejection fraction (EF) of 15%, and a heart rate of 80, produces a cardiac output of 4.5 l/min. After LVVRS for DCM to reduce the LV volume to 315 ml, the EF is unchanged, but the cardiac output drops by 0.7 l/min. In LV aneurysms, a LVDV of 380 ml, EF of 15%, and a heart rate of 80, produces a cardiac output of 4.5 l/min. After LVVRS for LVA reducing the LV volume to 320 ml, the EF increases to 56%, and the predicted cardiac output doubles. LVVRS is potentially very hazardous in the setting of DCM, confirmed by the international registry report and the Surgical Treatment for Ischemic Heart Failure Trial. However, in the setting of LVA, the surgery can result in marked improvement in cardiac output. The effect on postoperative cardiac output, due to the extent of LV resection can potentially be modelled for preoperatively.

Long-term survival of non-smokers undergoing coronary artery bypass surgery

OBJECTIVESnWe sought to investigate long-term survival of non-smokers undergoing coronary artery bypass surgery (CABG).nnnMETHODSnA prospective database of consecutive patients was retrospectively analysed and cross correlated with the UK strategic tracking service to evaluate survival after primary CABG. Univariate, multivariate and a propensity analyses were performed.nnnRESULTSnWe analysed 13 337 primary CABG procedures. Median follow-up was 7 years. Kaplan-Meier survival curves demonstrate that non-smokers have a significantly improved long-term survival compared with ex- and current smokers, P < 0.0001. Cox regression analysis identified smoking status, age, diabetes, ejection fraction (EF), body mass index, cerebrovascular disease, dialysis, left internal mammary artery (LIMA) non-usage, postoperative creatinine kinase muscle-brain isoenzyme (CKMB), radial artery usage, preoperative rhythm, forced vital capacity (FVC) and logistic EuroSCORE as significant risk factors determining long-term survival. Propensity matching resulted in 3575 non-smokers being matched 1:1, with ex-smokers. After matching, univariate analysis demonstrated the significantly worse long-term survival of ex-smokers compared with non-smokers, P < 0.0001. Cox regression analysis identified smoking status, age, postoperative CKMB, cerebrovascular disease, dialysis, diabetes, EF, FVC, LIMA non-usage, radial artery used, sinus rhythm and logistic EuroSCORE as significant risk factors determining long-term survival. Survival by smoking status plotted at the mean of the covariates, prepropensity matching, demonstrated that non-smokers had a significantly better long-term survival than ex-smokers, P < 0.0001; however, after propensity matching, non-smokers under 65 years of age had a significantly worse long-term survival compared with ex-smokers, P < 0.0001.nnnCONCLUSIONSnNon-smokers under the age of 65 years of age have significantly worse long-term survival compared with ex-smokers after risk factor adjustment. We speculate that this is because ex-smokers have had the causative factor, smoking, removed, but non-smokers have not.

Pneumonectomy in the seventh decade in a patient with a congenital uncorrected ventricular septal defect.

We describe the successful treatment of a patient in his seventh decade with a congenital uncorrected ventricular septal defect (VSD), moderate aortic stenosis and carcinoma of the lung, who underwent a successful pneumonectomy. Preoperative and intraoperative assessment of pulmonary artery pressure are essential to manage this combination of cardiac and thoracic pathologies. After pneumonectomy, echocardiography can be difficult. Magnetic resonance imaging (MRI) is useful to assess intra-cardiac defects in this situation.

Re: Bronchiolo-alveolar lung cancer: occurrence, surgical treatment and survival.

Furak et al. [1] provide interesting data on bronchioloalveolar (BAC) lung cancer: occurrence, surgical treatment and survival; however, their pathological classification [2,3] as to what constitutes a BAC is not the current World Health Organization (WHO) definition [4]. Furak et al. defined BAC as an adenocarcinoma if more than 50% of the adenocarcinoma had a BAC component. The WHO classifies an adenocarcinoma with a BAC component as ‘adenocarcinoma mixed type with predominant bronchioloalveolar pattern’, regardless of the percentage of the BAC component. Most tumours described as BAC in the past would now be in this category. The present definition of BAC is much morerestrictive thananypreviouslyusedbymanypathologists.

The right gastroepiploic artery: an independent risk for leak post oesophageal resection.

Numerous different operations exist for the treatment of oesophageal cancer, Ivor-Lewis, McKeown, and left thoracophrenotomy* being the most common. All rely on the stomach being utilised as a replacement conduit in the chest. To achieve this, the left gastric artery, a variable amount of the lesser curve (depending on individual surgeon preferences) and the short gastric arteries are divided. This enables the stomach to be swung up into the chest, relying on the gastroduodenal artery and then the right gastroepiploic artery to supply the fundus where the anastomosis takes place. Atheroma and size variability (diameter 2.0–3.5 mm, results in 9.4 times difference in flow by Poiseuilles law) of the right gastroepiploic artery is known from cardiac surgery where it is utilised as a bypass graft.1 This could potentially limit the blood supply at the anastomosis, increasing the chances of a leak postoperatively. n n[*Thoracophrenotomy = Thoracotomy and division of diaphragm.]

Letter by Poullis and Warwick Regarding Article, “Paradoxical Low-Flow, Low-Gradient Severe Aortic Stenosis Despite Preserved Ejection Fraction Is Associated With Higher Afterload and Reduced Survival”

To the Editor:nnIn their article, Hachicha et al1 raise a number of key points that merit further questioning. Despite the direct relevance of their findings to everyday clinical practice, it is our opinion that their use of the terms paradoxical low-flow and higher afterload may be flawed.nnThe gradient across a stenotic valve can be estimated using the Bernoulli equation (4V2). The velocity across a stenosis equals flow divided by …