Dilatation of the ascending aorta in patients with congenitally bicuspid aortic valves.

INTRODUCTION: The cause of ascending aortic dilatation occurring in patients with congenitally bicuspid aortic valves was investigated. METHODS: Flow patterns through human aortic roots with congenitally bicuspid aortic valves as well as through porcine constricted aortas were studied in a left heart simulator. Vibration was recorded as a measure of turbulence in the post-stenotic segment. Histological changes in fetal aortas with isolated congenitally bicuspid aortic valves were compared to fetal aortas with congenitally bicuspid aortic valves and hypoplastic left hearts, as well as to normal fetal aortas with tricuspid aortic valves. RESULTS: Congenitally bicuspid aortic valves were anatomically stenotic even in the absence of pressure gradients and without history of relevant symptoms. Histology of the aortic wall in isolated fetal congenitally bicuspid aortic valves was similar to that of fetal aortas with normal tri-leaflet aortic valves, but was abnormal if congenitally bicuspid aortic valves was associated with other cardiovascular anomalies. Flow studies revealed that turbulence and vibration in the post-stenotic aortic segments generated by the stenosis were proportional to the degree of the narrowing. CONCLUSIONS: Congenitally bicuspid aortic valves are inherently stenotic, asymmetrical, generate turbulence and vibration. This not only leads to early failure but also to injury of the ascending aortic wall and ascending aortic dilatation. The more progressive form of ascending aortic dilatation occurs in patients where congenitally bicuspid aortic valves is combined with other inborn anomalies and may require a radical procedure (replacement).

Surgical correction of pectus excavatum. How did we get here? Where are we going?

The currently applied techniques recommended for the repair of pectus excavatum anomalies are discussed, set against a historical review of early clinical studies and surgical interventions. The issues of the future direction pectus excavatum surgery may take are analyzed in detail, with the reviewer expressing reservations in connection with the recent trend to closed repair and concern over the potential for serious complications associated with the application of this technique.

Quality improvement in cardiac critical care.

Our quality improvement program began in 2004 to improve cardiac surgery outcomes. Early tracheal extubation in the cardiovascular intensive unit was utilized as a multidisciplinary driver for the quality improvement program. Continuous improvement in the rate of early extubation to drive multidisciplinary quality improvement in cardiac critical care correlated with decreased mortality, morbidity, and improved operational efficiency. Supportive educational efforts included, but were not limited to, principles of change, trust, competing values, crew resource management, evidence based medicine, and quality improvement.

Can timing of tracheal extubation predict improved outcomes after cardiac surgery?

INTRODUCTION: Early tracheal extubation is a common goal after cardiac surgery. Our study aims to examine whether timing of tracheal extubation predicts improved postoperative outcomes and late survival after cardiac surgery. We also evaluated the optimal timing of extubation and its association with better postoperative outcomes. METHODS: Between 2002 and 2006, 1164 patients underwent early tracheal extubation (<6 hours after surgery) and 1571 had conventional extubation (>6 hours after surgery). Propensity score adjustment and multivariable logistic regression analysis were used to adjust for imbalances in the patients' preoperative characteristics. Receiver operating characteristic curves (ROC) were used to identify the best timing of extubation and improved postoperative outcomes. Cox regression analysis was used to identify whether early extubation is a risk factor for decreased late mortality. RESULTS: Results - Early extubation was associated with lower propensity score-adjusted rate of operative mortality (Odds Ratio =0.55, 95% Confidence Intervals =0.31-0.98, p=0.043). Extubation within 9 hours emerged as the best predictor of improved postoperative morbidity and mortality (sensitivity =85.5%, specificity =52.7%, accuracy =64.5%). Early extubation also predicted decreased late mortality (Hazard Ratio =0.45, 95% Confidence Intervals 0.31-0.67, p<0.001). CONCLUSIONS: Early extubation may predict improved outcomes after cardiac surgery. Extubation within 9 hours after surgery was the best predictor of uncomplicated recovery after cardiac surgery. Those patients intubated longer than 16 hours have a poorer postoperative prognosis. Early extubation predicts prolonged survival up to 16 months after surgery.

Finite element modeling of the thoracic aorta: including aortic root motion to evaluate the risk of aortic dissection.

OBJECTIVE: We propose that the aortic root motion plays an important role in aortic dissection. METHODS AND RESULTS: A finite element model of the aortic root, arch and branches of the arch was built to assess the influence of aortic root displacement and pressure on the aortic wall stress. The largest stress increase due to aortic root displacement was found at approximately 2 cm above the top of the aortic valve. There, the longitudinal stress increased by 50% to 0.32 MPa when 8.9 mm axial displacement was applied in addition to 120 mmHg luminal pressure. A similar result was observed when the pressure load was increased to 180 mmHg without axial displacement. CONCLUSIONS: Both aortic root displacement and hypertension significantly increase the longitudinal stress in the ascending aorta, which could play a decisive role in the development of various aortic pathologies, including aortic dissection.

A prelude to Fontan.

In the decades preceding the Fontan operation, there was an intensive experimental and clinical quest to bypass the right heart. Whereas right heart bypass was successfully achieved in animal experiments, clinically only partial bypass (superior cava-right pulmonary artery anastomosis) was applied successfully. This intensive experimental and clinical activity provided the background for the Fontan operation.

Acquired deformities of the anterior chest wall.

BACKGROUND: Acquired chest wall deformities are difficult to describe and to classify. We propose the following classification and treatment options. METHODS: We observed 11 patients with acquired deformities (AD) that required surgical correction. RESULTS: AD of the chest can be classified into 4 groups: (1) AD resulting from a pathological process within the thorax (heart enlargement, mediastinal tumors), (2) AD resulting from chest wall disease (rib osteomyelitis or tumors), (3) iatrogenic deformities (following rib graft harvesting, acquired Jeune's syndrome), and (4) post-traumatic deformities. Group 1 requires treatment of the pathological process. Group 2 is guided by oncological or infectious disease principles. Groups 3 and 4 require chest wall reconstruction. Iatrogenic AD usually occur after pectus excavatum repair with rib cartilage extirpation in young patients, which results in a reduced, restricted thorax. Post-traumatic AD often have pathological chest wall mobility owing to pseudo-articulation of injured ribs. CONCLUSIONS: To prevent AD formation and to protect thoracic growth and mobility, costosternal and costochondral junctions should be preserved during cartilage resection. Substernal suturing of the perichondrium should be avoided.

Changes in sternal blood flow after different methods of internal thoracic artery harvesting.

OBJECTIVE: The study was designed to assess the early changes in sternal perfusion after midline sternotomy and different (skeletonized versus semiskeletonized) techniques of internal thoracic artery (ITA) harvesting. METHODS: The experiments were performed in the swine model. After midline sternotomy, ITA harvesting (skeletonized technique) was performed unilaterally in Group I (6 animals). The ITA and the internal thoracic vein (ITV) were harvested (semiskeletonized technique) in Group II (5 animals). The contralateral sternal half served as a control. Using a thermographic camera with a 0.06 degrees C sensitivity, sternal perfusion was assessed 2 and 5 hours after surgery. RESULTS: Midline sternotomy alone did not affect sternal blood flow. A statistically significant ( p < 0.05) reduction in perfusion of the involved sternal half in comparison to the control side was detected at 2 and 5 hours after surgery. The degree of perfusion deficit was not related to the harvesting technique. CONCLUSIONS: Skeletonized and semiskeletonized ITA harvesting techniques caused a similar acute reduction in sternal perfusion during the early postoperative period and this effect lasted for at least 5 hours.

From Hippocrates to Palmaz-Schatz, the history of carotid surgery.

The extracranial carotid artery is the most common site for peripheral vascular procedures. Although the association of carotid disease and neurologic dysfunction was understood by the ancient Greeks, over 1700 years would pass before the relevant anatomy was described. In the 16th and 17th centuries, attempts at treatment of carotid injury and aneurysm by ligation were met with extremely high rates of stroke and death. It is not until the mid 20th century, with the introduction of carotid angiography and improved vascular surgical techniques, that the era of reconstructive carotid surgery begins. We present a synopsis of the history of carotid surgery from ancient times to present day.

Effect of thrombus on abdominal aortic aneurysm wall dilation and stress.

AIM: Our goal is to understand how a mural thrombus may influence the pressure transmitted to and the dilation experienced by the abdominal aortic aneurysm (AAA) wall. METHODS: Two intact AAAs with mural thrombus were removed from patients and pressurized to 100 mmHg. The pressure was measured using a micro-tip needle transducer inserted in the aneurysm wall and advanced through the thrombus. In 1 patient with AAA, similar measurements were made in vivo. Also, in vitro, in the two aneurysms the dilation as a function of pressure was measured using the markers on the surface before and after the thrombus was removed. RESULTS: Both, in vitro and in vivo, in the presence of the thrombus the pressure transmitted to the aneurysm wall was 91+/-10% of luminal pressure and at 6 mm from the wall it was 96+/-5%. The aneurysm dilated more in the pressure range of 0-40 mmHg (2-8%) than in the range of 40-100 mmHg (0.4-1.8%). Upon removal of the thrombus these dilations increased significantly to 4-15% and 0.9-3.3%, respectively. Overall, the strains (dilation) in the circumferential and longitudinal directions were similar before the thrombus was removed. CONCLUSIONS: Even though the thrombus allows the transmission of luminal pressure to the aneurysm wall, it may prevent the aneurysm from rupture by diminishing the strain on the wall. Consistent with this, a mechanical model of the thrombus proposed is "a thrombus as a fibrous network adherent to the aneurysm wall".

Mechanical stress as cause of aortic valve disease. Presentation of a new aortic root prosthesis.

We present an overview of studies on the aortic valve and propose that mechanical stress is a main causative factor in the degenerative valvular disease. In the normal aortic valve, the leaflets have a smooth surface, free of wrinkles and creases, throughout the opening process. This smooth leaflet surface during motion is achieved by the "pull and release" movement of the commissures, which occurs because of the compliance of the aortic root. When the aortic root is stiffened, either by artificial means or by the loss of elasticity due to aging, the leaflet dynamics change significantly. The leaflets develop a significant number of creases and wrinkles during the opening process. In the bileaflet valve, the leaflets develop similar creasing and wrinkling during the opening process. This happens mainly due to the less-than-ideal design of the bileaflet valve and in spite of the compliant aortic root. When the aortic valve is spared using a noncompliant tube graft, a similar phenomenon of leaflet creasing occurs. Because the creasing produces high stresses from bending and buckling, it is damaging to the leaflet tissue and can lead to degenerative and calcific valvular disease. Based on these observations a new aortic root prosthesis with compliant sinuses has been designed for the valve sparing operation.

Mechanical properties of abdominal aortic aneurysm wall.

There is a need to understand why and where the abdominal aortic aneurysm may rupture. Our goal therefore is to investigate whether the mechanical properties are different in different regions of the aneurysm. Aorta samples from five freshly excised whole aneurysms, > or = 5 cm in diameter, from five patients, average age 71 +/- 10 years, were subjected to uniaxial testing. We report the wall thickness, yield stress and strain, and parameters that describe nonlinear stress-strain curves for the anterior, lateral and posterior regions of the aneurysm. The posterior region was thicker than the anterior region (2.73 +/- 0.46 mm versus 2.09 +/- 0.51 mm). The stress-strain curves were described by sigma = a epsilon(b), where sigma is true stress and epsilon is engineering strain. In the circumferential direction, the wall stiffness increased from posterior to anterior to lateral. In the longitudinal direction, the lateral and anterior regions showed greater wall stiffness than the posterior region. The wall stiffness was greater in the circumferential than longitudinal direction. The anterior region was the weakest, especially in the longitudinal direction (yield stress sigmaY = 0.38 +/- 0.18 N mm(-2)). For a less complex model the aneurysmal wall could be considered orthotropic with sigma = 12.89epsilon(2.92) and 4.95epsilon(2.84) in the circumferential and longitudinal directions. For the isotropic model, sigma =7.89epsilon(2.88). In conclusion, different regions of the aneurysm have different yield stress, yield strains, and other mechanical properties, and this must be considered in understanding where the rupture might occur.

Wall stress studies of abdominal aortic aneurysm in a clinical model.

To estimate when an abdominal aortic aneurysm (AAA) may rupture, it is necessary to understand the forces responsible for this event. We investigated the wall stresses in an AAA in a clinical model. Using CT scans of the AAA, the diameter and wall thickness were measured and the model of the aneurysm was created. The wall stresses were determined using a finite element analysis in which the aorta was considered isotropic with linear material properties and was loaded with a pressure of 120 mmHg. The AAA was eccentric with a length of 10.5 cm, a diameter of 2.5 to 5.9 cm, and a wall thickness of 1.0 to 2.0 mm. The aneurysm had specific areas of high stress. On the inner surface the highest stress was 0.4 N/mm2 and occurred along two circumferentially oriented belts--one at the bulb and the other just below. The stress was longitudinal at the anterior region of the bulb and circumferential elsewhere, suggesting that a rupture caused by this stress will result in a circumferential tear at the anterior portion of the bulb and a longitudinal tear elsewhere. In the mid-surface the highest stress was 0.37 N/mm2 and occurred at two locations: the posterior region of the bulb and anteriorly just below. The stress was circumferential, suggesting that the rupture caused by this stress will produce a longitudinal tear. The location and orientation of the maximum stress were influenced more by the tethering force than by the wall thickness, luminal pressure, or wall stiffness. In conclusion, the rupture of an AAA is most likely to occur on the inner surface at the bulb. Such analytical approaches could lead to a better understanding of the aneurysm rupture and may be instrumental in planning surgical interventions.

A new aortic root prosthesis with compliant sinuses for valve-sparing operations.

BACKGROUND: We designed and tested a novel aortic root prosthesis with compliant sinuses for valve-sparing operations. METHODS: In eight human aortic roots, the aorta was trimmed 2 mm above the leaflet attachment. The aortic portion of the graft was made by scalloping the Dacron tube. Three sinuses were made individually after turning z-folds in the fabric 90 degrees. Three rectangular pieces were cut and purse strings sewn in each to form the sinuses. The graft was sutured to the aortic root and studied in a left heart simulator. The leaflet motion was recorded (500 frames/second), commissural movement was measured with ultrasound, and the shape of the root was determined from a mold. Seven intact aortic roots were also studied. RESULTS: In the aortic graft roots, the valves were competent and leaflets opened rapidly into a circular orifice, not touching the sinus wall. Commissural diameter increased by 22% when pressure increased from 0 to 80 mm Hg, and increased by a further 6.6% when pressure increased to 120 mm Hg. The sinuses had a teardrop shape. CONCLUSIONS: The dynamics of the aortic graft root and the leaflets were comparable to that of the intact aortic root. This prosthesis is being introduced in clinical practice.

The influence of patient strength, aerobic capacity and body composition upon outcomes after coronary artery bypass grafting.

BACKGROUND: Physical activity, physical fitness and body habitus of patients may be important predictors of outcomes after cardiac surgery. This study sought to quantify physical fitness and determine whether components of fitness enhance the prediction of outcomes in a group of patients undergoing coronary artery bypass grafting. METHODS: A group of 200 patients were evaluated prior to coronary artery bypass surgery. A Veterans Specific Activity Questionnaire (VSAQ) measured aerobic capacity. A grip dynamometer assessed strength. Skin-fold thickness was used to calculate percent body fat and lean body mass index. Patients were divided into low risk (0-2.5%) and high risk (>2.5%) groups based on the STS National Cardiac Surgery Database prediction of operative mortality. RESULTS: Patients with both a high percent body fat and a low VSAQ were at higher risk for at least one serious complication (p<0.05) and a longer postoperative length of stay (p<0.05). CONCLUSION: This study suggests: 1) An index of physical fitness can be obtained preoperatively in cardiac surgical patients; 2) This information aids in the prediction of operative risk.