Jose A. Navia

Coronary Venous Retroperfusion: An Old Concept, a New Approach

The potential of the coronary veins for revascularization has been evaluated by many investigators for more than a century. The major hurdle has been the damage of veins during sudden exposure to arterial pressure. The solution to this problem has typically involved the use of intricate and complicated apparatus and devices, which has prevented routine clinical utility in the catheterization laboratory. This review examines this old concept from a new perspective and proposes a novel hypothesis to address previous shortcomings. We speculate on an approach that may serve to eliminate the edema and hemorrhage that result during venous retroperfusion as the pressure is suddenly increased to arterial values. We propose the rationale to increase the venous pressure to arterial values more gradually to allow prearterializations of the veins before full exposure of arterial pressure. Finally, we discuss various possible indications for this selective autoretroperfusion strategy to combat myocardial ischemia in cardiogenic shock patients, ST-elevation myocardial infarct patients, no-option patients, and beyond.

Proper Orientation of the Graft Artery Is Important to Ensure Physiological Flow Direction

Arterial grafts such as right internal mammary artery (RIMA), radial artery (RA) or epigastric artery are being used with increasing frequency as free grafts or as composite grafts with left internal mammary artery (LIMA). Currently, there is no consideration of the orientation of the free artery graft to mimic the in vivo state. Hence, some grafts may be oriented such that the direction of blood flow exerted on the endothelium is reversed relative to the in vivo condition. Previous studies have shown that transient flow reversal lead to atherogenesis. A recent study demonstrated that nitric oxide is significantly reduced during reverse flow and the reduction is mediated through an increase in superoxide production. In light of these data, we suggest that the flow direction is important and recommend the assurance of proper orientation of the free arterial graft. Furthermore, we propose a new surgical procedure to modify the composite LIMA-RA or LIMA-RIMA configuration as a horseshoe or K composite graft to ensure proper orientation of the flow direction relative to the endothelium.

A new method of myocardial revascularization with the radial artery

We present a new method of myocardial revascularization. The radial artery is used in combination with the left internal mammary artery, thereby providing three distal end-to-side anastomoses to the left anterior descending coronary artery and other sites as determined by the coronary artery lesions. Arterial conduits form an anastomotic network between the left internal mammary artery and the radial artery in a horseshoe pattern. Three coronary arteries are revascularized by two arterial conduits in the left coronary system.

Mild anastomotic stenosis in patient-specific CABG model may enhance graft patency: a new hypothesis.

It is well known that flow patterns at the anastomosis of coronary artery bypass graft (CABG) are complex and may affect the long-term patency. Various attempts at optimal designs of anastomosis have not improved long-term patency. Here, we hypothesize that mild anastomotic stenosis (area stenosis of about 40–60%) may be adaptive to enhance the hemodynamic conditions, which may contribute to slower progression of atherosclerosis. We further hypothesize that proximal/distal sites to the stenosis have converse changes that may be a risk factor for the diffuse expansion of atherosclerosis from the site of stenosis. Twelve (12) patient-specific models with various stenotic degrees were extracted from computed tomography images using a validated segmentation software package. A 3-D finite element model was used to compute flow patterns including wall shear stress (WSS) and its spatial and temporal gradients (WSS gradient, WSSG, and oscillatory shear index, OSI). The flow simulations showed that mild anastomotic stenosis significantly increased WSS (>15 dynes⋅cm−2) and decreased OSI (<0.02) to result in a more uniform distribution of hemodynamic parameters inside anastomosis albeit proximal/distal sites to the stenosis have a decrease of WSS (<4 dynes⋅cm−2). These findings have significant implications for graft adaptation and long-term patency.

Stroke Propensity Is Increased under Atrial Fibrillation Hemodynamics: A Simulation Study

Atrial fibrillation (AF) is the most common sustained dysfunction in heart rhythm clinically and has been identified as an independent risk factor for stroke through formation and embolization of thrombi. AF is associated with reduced cardiac output and short and irregular cardiac cycle length. Although the effect of AF on cardiac hemodynamic parameters has been reported, it remains unclear how the hemodynamic perturbations affect the potential embolization of blood clots to the brain that can cause stroke. To understand stroke propensity in AF, we performed computer simulations to describe trajectories of blood clots subject to the aortic flow conditions that represent normal heart rhythm and AF. Quantitative assessment of stroke propensity by blood clot embolism was carried out for a range of clot properties (e.g., 2–6 mm in diameter and 0–0.8 m/s ejection speed) under normal and AF flow conditions. The simulations demonstrate that the trajectory of clot is significantly affected by clot properties as well as hemodynamic waveforms which lead to significant variations in stroke propensity. The predicted maximum difference in stroke propensity in the left common carotid artery was shown to be about 60% between the normal and AF flow conditions examined. The results suggest that the reduced cardiac output and cycle length induced by AF can significantly increase the incidence of carotid embolism. The present simulations motivate further studies on patient-specific risk assessment of stroke in AF.

Fluid-structure interaction in aortic cross-clamping: Implications for vessel injury

Vascular cross-clamping is applied in many cardiovascular surgeries such as coronary bypass, aorta repair and valve procedures. Experimental studies have found that clamping of various degrees caused damage to arteries. This study examines the effects of popular clamps on vessel wall. Models of the aorta and clamp were created in Computer Assisted Design and Finite Element Analysis packages. The vessel wall was considered as a non-linear anisotropic material while the fluid was simulated as Newtonian with pulsatile flow. The clamp was applied through displacement time function. Fully coupled two-way solid-fluid interaction models were developed. It was found that the clamp design significantly affected the stresses in vessel wall. The clamp with a protrusion feature increased the overall Von Mises stress by about 60% and the compressive stress by more than 200%. Interestingly, when the protrusion clamp was applied, the Von Mises stress at the lumen (endothelium) side of artery wall was about twice that of the outer wall. This ratio was much higher than that of the plate-like clamp which was about 1.3. The flow reversal process was demonstrated during clamping. Vibrations, flow and wall shear stress oscillations were detected immediately before total vessel occlusion. The commonly used protrusion clamp increased stresses in vessel wall, especially the compressive stress. This design also significantly increased the stresses on endothelium, detrimental to vessel health. The present findings are relevant to surgical clamp design as well as the transient mechanical loading on the endothelium and potential injury. The deformation and stress analysis may provide valuable insights into the mode of tissue injury during cross-clamping.

A transatrial pericardial access: lead placement as proof of concept

A safe, easy, and quick access into the pericardial space may provide a window for diagnostics and therapeutics to the heart. The objective of this study was to provide proof of concept for an engagement and access catheter that allows access to the pericardial space percutaneously. A multilumen catheter was developed to allow navigation and suction fixation to the right atrial appendage/wall in a normal swine model. Advancement through the multilumen catheter using a second catheter with a distal needle tip allows access to the pericardial space without pericardial puncture and advancement of a standard guide wire into the space. Navigation into the pericardial space was undertaken by fluoroscopy alone and was accomplished in 10 swine (5 acute and 5 chronic). As a specific application of this pericardial access method, a pacing lead was implanted on the epicardial surface. Five chronic swine experiments were conducted with successful pacing engagement verified by lead impedance and pacing threshold and sensing. Lead impedance exceeded 1,000 Omega preengagement and dropped by an average of 200 Omega upon implant (769 +/- 498 Omega). Pacing thresholds at 0.4 ms ranged from approximately 0.5 to 2.1 V acutely (1.03 +/- 0.92 V). No cardiac effusion or tamponade was observed in any of the acute or chronic studies. The ability to engage, maintain, and retract the right atrial appendage/wall and to engage an epicardial lead was successfully demonstrated. These findings support the feasibility of safe access into the pericardial space in a normal swine model and warrant further investigations for clinical translation.

Novel gastric sleeve magnetic implant: safety and efficacy in rats

BACKGROUND The prevalence of obesity is growing worldwide and has reached epidemic proportions. Vertical sleeve gastrectomy, which requires irreversible removal of gastric tissue, is considered an effective weight loss treatment of severe obesity. The aim of the present study was to evaluate the feasibility of a reversible gastric sleeve magnetic implant that mimics the vertical sleeve gastrectomy without the gastrectomy for weight loss in a group of normal and obese rats. METHODS A group of Zucker fatty rats either underwent surgical implantation or a sham operation and were followed up for 6 weeks. Also, a group of Wistar rats underwent surgical implantation for 6 weeks, followed by surgical implant removal at 6 weeks, and recovery for an additional 4 weeks. Food intake and body weight were monitored after surgery to determine the efficacy of the device. A histologic examination for all rats was made to evaluate the change in the gastric wall in response to gastric sleeve magnetic implantation. RESULTS The implanted Zucker fatty and Wistar rats showed a statistically significant decrease in food intake and weight gain rate compared with the sham-operated rats (approximately 3%/wk of body weight loss in the treated group). Moreover, the decrease in the weight gain rate was sustained for 4 weeks after removal of the magnetic implant. The histologic evidence revealed an inflammatory mononuclear cell infiltration and mild fibrosis and hyperplasia of blood vessels, as expected for any implant. No significant structural damage, tissue ischemia, hemorrhage, or necrosis was found in the gastric wall. CONCLUSION Our results have shown that the device is feasible in rats, results in effective weight loss, and can be easily removed. These findings, along with the lack of the need for resection of the native stomach, provide a compelling basis for additional development of the device in large animal models.

Thrombus deflector stent for stroke prevention: A simulation study

Atrial fibrillation (AF) is a dysfunction of heart rhythm and represents an increased predisposition to ischemic stroke in AF patients. It has been shown that the AF-induced hemodynamic conditions may contribute to the increased embolic propensity through the carotid arteries. We simulated a stroke-prevention device with a unique strut structure to deflect the trajectory of a blood clot to the carotid artery. We identified the important determinants of functionality in a device design using computational fluid dynamics simulations. Quantitative assessment of deflection efficacy over various clot dimensions was carried out for the device with different strut configurations under AF flow conditions. The simulations demonstrate that the trajectory of a clot destined to the left common carotid artery (LCCA) can be deflected by a strut-structured device at the LCCA inlet with virtually no change in flow resistance. The deflection efficacy of the device is dependent on the clot properties and strut designs of the device. A configuration of 0.75 mm thick and 0.75 mm distant struts with 50% of surface convexity were found to provide maximum deflection efficacy (e.g., 36% greater deflection efficacy than a flat filter) among the strut structures considered. The results suggest that a deflector stent implanted in the aortic branch may be an effective stroke-prevention device. The present simulations motivate pre-clinical animal studies as well as further studies on patient-specific design of the device that maximize the deflection efficacy while minimizing device safety issues.

In vitro performance of the novel coronary sinus AutoRetroPerfusion Cannula.

Myocardial salvage through coronary sinus intervention has been documented. The AutoRetroPerfusion Cannula is a novel device that is able to perfuse the coronary bed retrogradely through the coronary sinus with arterial blood generated from a peripheral artery with no need for a pump. The cannula consists of a distal end that, once secured in the coronary sinus, opens an umbrella-like membrane to create pressure in the coronary sinus, and at the same time has small channels directed backwards to the right atrium to provide pressure relief. The cannula is introduced from the axillary vein under local anesthesia and the proximal end, which consists of a graft, is anastomosed to the axillary artery to start autoperfusion once the distal end is secured in the coronary sinus and the occluding membrane is open. The AutoRetroPerfusion Cannula was tested in the in vitro mock loop under 50–120 mm Hg of proximal pressure and 50, 100, and 150 ml/min of total flow in the cannula. We were able to achieve the nominal design point of 40–80 mm Hg of distal pressure and 50–150 ml/min of distal flow by adjusting the number, diameter, and length of the small backwards channels.