Centrifugal pumps as left ventricular assist for coronary revascularization on a beating heart

Haemodynamic changes during left anterior descending artery exposure in off-pump coronary artery bypass: comparison between use of moist laparotomy pads and deep pericardial traction sutures for heart displacement

Haemodynamic changes occurring during heart displacement, using moist laparotomy pads placed behind the heart (PAD group, n = 26) or deep pericardial traction sutures (DPS group, n = 25) to facilitate exposure of the left anterior descending artery during off-pump coronary artery bypass surgery, were compared. Haemodynamic variables were assessed before and 10 min after displacement of the heart. The central venous pressure, mean pulmonary artery pressure and pulmonary capillary wedge pressure increased in both groups. After heart displacement in the PAD group, the cardiac index, stroke volume index, mixed venous oxygen saturation, right ventricular ejection fraction and left ventricular stroke work index decreased significantly, and the systemic vascular resistance and pulmonary vascular resistance increased significantly; these parameters remained unchanged in the DPS group. It was concluded that displacement of the heart using moist laparotomy pads caused significant haemodynamic derangement compared with that caused by deep pericardial traction sutures.

Minimally ischemic off-pump coronary artery bypass grafting: active perfusion-assist with nitroglycerin-supplemented blood

During off-pump coronary artery bypass surgery, concern remains about possible myocardial injury associated with the transient occlusion and stabilization of the target vessels. To try to minimize myocardial ischemia and achieve hemodynamic stability, we used a coronary perfusion catheter combined with the perfusion-assisted direct coronary artery bypass system, which enables active and modified coronary perfusion of the target vessel throughout the duration of multiple grafting.

A coronary active perfusion system for off-pump coronary artery bypass: advantage over passive perfusion regarding the physiology of the coronary artery

To avoid myocardial ischemia during off-pump coronary artery bypass, we developed a coronary active perfusion system (CAPS) that perfuses arterial blood to the coronary artery at the diastolic phase of the cardiac cycle by a syringe pump system. We report herein the details and compare CAPS with a passive shunt circuit from the femoral artery (FA shunt), regarding the physiology of the coronary artery. Six pigs were used for this study. After CAPS or FA shunt perfusion was established, coronary flow and coronary pressure were measured. The coronary flows in the native coronary artery, FA shunt perfusion, and CAPS perfusion with syringe pump stroke volume settings ranging from 0.1 to 0.4 ml were 27.2+/-3.0, 4.1+/-1.5, 12.7+/-1.2, 24.8+/-1.9, 33.3+/-1.6, and 42.2+/-1.9 ml/min, respectively. Mean coronary pressures under FA shunt perfusion and CAPS perfusion with stroke settings from 0.1 to 0.4 ml were 23.7+/-4.6, 48.8+/-5.0, 61.3+/-7.5, 70.8+/-5.4, and 82.3+/-5.2 mm Hg, respectively. CAPS had an advantage over the FA shunt regarding coronary flow with safe coronary pressure. Using CAPS, an off-pump coronary artery bypass can be performed safely without myocardial ischemia.

Circulatory support for OPCAB procedures

During off-pump coronary artery bypass grafting (OPCAB) which allows complete revascularization through a median sternotomy, revascularization of the lateral and posterior walls requires the verticalization of the heart, which may cause haemodynamic disturbance. This concern has stimulated the development of circulatory support with mini-pumps. Initially, these pumps were designed for the right side of the heart, which was found to be the main contributor to haemodynamic instability under experimental conditions. The three types of mini-pumps that have been developed so far - two for the right side of the heart and one for both sides - are reviewed as well as a new concept of integrated cardiopulmonary bypass (CPB) circuit with reduced surface and priming volume. However, with increasing experience and improved methods of exposition, OPCAB has become a procedure that can be performed without support in the majority of the cases. Nevertheless, the concept of miniaturization and the possibility to insert these devices through a peripheral access has opened the way to new indications, mainly short-term circulatory support for acute heart failure. This development is welcome in a field where available devices are invasive and plagued with a heavy morbidity.

Preserved myocardial blood flow and oxygen supply-demand balance with active coronary perfusion during simulated off-pump coronary artery bypass grafting

BACKGROUND

During off-pump coronary artery bypass surgery, concern remains about the possible myocardial injury associated with the transient occlusion and stabilization of the target vessels. Although intraluminal shunts are used to avoid ischemia during graft anastomosis, blood flow through the shunts can be affected by upstream pressure and inherent resistance, resulting in reduced blood flow during hypotension or severe proximal stenosis.

METHODS

In anesthetized dogs regional myocardial blood flow (microspheres), oxygen consumption, lactate extraction, and systolic shortening (sonomicrometry) were measured in the myocardium served by the left anterior descending coronary artery with native perfusion after interposition of a 2.25-mm shunt (> or = 90% of left anterior descending diameter) and during active coronary perfusion with a constant flow pump. Measurements were made under normotension and hypotension produced by partial caval occlusion to reduce arterial pressure by 50%.

RESULTS

Interposition of the shunt reduced blood flow by 67.8%, regional oxygen delivery by 59.8%, and systolic shortening by 45.6% relative to baseline, but lactate extraction (31.0% vs 31.2%) and oxygen supply-consumption (O(2)S/myocardial oxygen consumption ratio, 2.7 +/- 0.5 vs 2.6 +/- 0.5) were comparable with baseline values. Hypotension further decreased these physiologic values and was associated with local lactate production (-67.4% extraction) and decreased O(2)S/myocardial oxygen consumption ratio (1.3 +/- 0.1). Active coronary perfusion was associated with regional blood flow, oxygen delivery, systolic shortening, and lactate extraction comparable with baseline values. In contrast to the shunt, active perfusion maintained myocardial flow, oxygen delivery, and lactate extraction during hypotension and normalized the O(2)S/myocardial oxygen consumption ratio, although systolic shortening decreased as a result of ventricular unloading.

CONCLUSION

Intraluminal shunts may impede oxygen delivery to the target myocardium, which precipitates regional ischemia during transient hypotension. Active coronary perfusion provides adequate oxygen supply independent of systemic blood pressure.

Hemocompatibility of a coaxial pump catheter for less invasive heart surgery

Off-pump coronary artery bypass (OPCAB) requires heart manipulation during exposure of the lateral and posterior walls of the heart, which may cause hemodynamic instability, mainly through right ventricular dysfunction. A coaxial atrial cannula connected to a minicentrifugal pump was developed to bypass the right heart. This study was designed to test the hemocompatibility of this pump ongoing for 6 h. In five calves (bodyweight, 70.3+/-4.2 kg), the pump was inserted and set to its maximal motor speed of 7000 rpm. Blood samples were taken for blood gas analyses, hematology and chemistry on an hourly basis. ANOVA was used for statistical analysis. During the 6-h run, hematocrit and red blood cell count were stable (p=0.77 and 0.87, respectively). Platelet count was not significantly altered (p=0.55). LDH was stable (p=0.61) and plasma free hemoglobin remained below 100 mg/l throughout the experiment. Adequate tissue perfusion was maintained as reflected by the stable mixed venous oxygen saturation (baseline, 72.5+/-2%, and 6 h, 65.6+/-3.4%) and no defect of any pump system was detected during this 6-h testing. This right heart minipump appears to have a minimal impact on red cells and platelets when set at its maximal speed for 6 h, underlining the hematological safety of the system.

Development of the MEDOS/HIA DeltaStream extracorporeal rotary blood pump

The DeltaStream blood pump has been developed for extracorporeal circulation with one focus on potential integration into simplified bypass systems (SBS). Its small size and an embedded electric motor are the basic pump properties. A variation of the impeller design has been performed to optimize hydraulic and hematologic characteristics. A simple impeller design was developed which allows flow and pressure generation for cardiopulmonary bypass applications. The option of a pulsatile flow mode for ventricular assist device applications also was demonstrated in vitro. Impeller washout holes were implemented to improve nonthrombogenicity. The pump was investigated for potential thermal hazards for blood caused by the integrated electric motor. It could be demonstrated that there is no thermal risk associated with this design. Durability tests were performed to assess the lifetime of the pump especially with regard to the incorporated polymeric seal. Seal lifetimes of up to 28 days were achieved using different blood substitutes. In animal tests using either the pump as a single device or in an SBS setup, biocompatibility, low hemolysis, and nonthrombogenicity were demonstrated. In summary, the DeltaStream pump shows great potential for different extracorporeal perfusion applications. Besides heart-lung machine and SBS applications, ventricular assist and extracorporeal membrane oxygenation up to several days also appear promising as potential applications.

Coronary artery bypass grafting using a miniature right ventricular support system

Cardiopulmonary bypass (CPB) with cardioplegic myocardial preservation has long been the gold standard for surgical care of coronary artery disease. More recently, alternatives to the conventional approach of CPB-myocardial revascularization have been developed. Epicardial stabilizing devices have been used to immobilize areas of the beating heart to provide a stable surface for some coronary anastomoses. These approaches are often limited to anterior aspects of the heart because revascularization of posterior and lateral vessels often requires the heart to be manipulated or contorted. Excessive manipulation can lead to hemodynamic compromise as a result of partially obstructing pulmonary blood flow. A miniature extracorporeal system has been developed that uses right ventricular support and allows for epicardial surgical procedures to be conducted on a beating heart without standard CPB. The extracorporeal system consists of a coaxial atrial cannula that is connected to a miniature centrifugal pump. Blood is drained from the right atrium, passes through the miniature centrifugal pump and is delivered through the cannula's inner reinfusion lumen into the pulmonary artery. The entire circuit volume is approximately 30 ml. The system is positioned on the sterile operative field. The pump is controlled by a console positioned adjacent to the patient. The centrifugal pump is capable of delivering blood flow at rates of 1-6 l/min. This extracorporeal system may be of benefit in maintaining adequate cardiac output during epicardial beating heart surgery.

Analysis of hemodynamic changes during beating heart surgical procedures

BACKGROUND

Coronary artery bypass grafting on the beating heart causes significant hemodynamic compromise during displacement of the heart. The precise mechanisms causing altered hemodynamics have not been clearly understood. The purpose of this study was to define the hemodynamic changes caused by displacing the heart in patients undergoing beating heart surgical procedures.

METHODS

Forty-four patients (35 men, 9 women; mean age, 64.5 +/- 9.6 years) underwent off-pump coronary artery bypass grafting. The hemodynamic variables were collected before and after positioning the heart for anastomosis of the left anterior descending, circumflex, and posterior descending coronary arteries.

RESULTS

There was a significant increase in right ventricular end-diastolic pressure during positioning for all vessels, and in left ventricular end-diastolic pressure during positioning for the left anterior descending and circumflex coronary arteries. Positioning for the circumflex artery showed the largest increase of left and right ventricular end-diastolic pressure, resulting in the greatest hemodynamic compromise.

CONCLUSIONS

In the clinical setting of diseased human hearts, there is a biventricular contribution to altered hemodynamics. The increase of right ventricular end-diastolic pressure in all positions suggests that the major cause of hemodynamic changes is disturbed diastolic filling of the right ventricle, especially by direct ventricular compression.

Right heart circulatory support facilities coronary artery bypass without cardiopulmonary bypass

BACKGROUND

Revascularization of the posterior wall often causes hemodynamic instability in beating heart coronary artery bypass (CAB). Our previous clinical studies have shown that tilting the heart primarily alters right-heart hemodynamics. The purpose of this study was to evaluate right-heart support in clinical cases.

METHODS

Seventeen patients underwent beating heart CAB with right-heart support. The right-heart support system (A-Med Systems, West Sacramento, CA) consisted of a coaxial cannula placed through the right atrium and the tip of the cannula positioned in main pulmonary artery. Blood was removed from the right atrium and returned to the main pulmonary artery.

RESULTS

Elective beating heart CAB was accomplished successfully in 17 patients with right-heart support. Anastomoses performed were left anterior descending coronary artery (11), diagonal (3), circumflex (5), obtuse marginal artery (11), and right coronary artery (10). Right-heart support between 1 and 3 L/min improved hemodynamics especially in the circumflex position. No device-related patient incidents occurred, nor were there incidents of infection or air embolism. All 17 patients were discharged to their homes.

CONCLUSIONS

The right-heart support system was safe without complications. Exposure of the posterior wall was possible in all cases without hemodynamic compromise.

Hemodynamic changes and right heart support during vertical displacement of the beating heart

BACKGROUND

Hemodynamic instability during heart displacement in off-pump multivessel coronary artery bypass grafting might be related to right heart dysfunction. The Enabler (HemoDynamics Systems Ltd, Upper Yoqneam, Israel) is a cannula pump that expels blood from the right atrium into the pulmonary artery. We studied the hemodynamic changes and the role of the enabler during heart displacement.

METHODS

Nine anesthetized sheep were assessed for hemodynamic changes during 90-degree heart displacement with or without Enabler support. Hemodynamic parameters included cardiac output, systemic arterial blood pressures, and left and right heart filling pressures.

RESULTS

Heart displacement caused a significant decrease in cardiac output and systemic blood pressure (46%+/-5%, p = 0.001; and 20%+/-5%, p = 0.009, respectively), with a concomitant 137%+/-24% (p = 0.003) increase in central venous pressure. No significant change in left atrial pressure was observed. Activation of the Enabler caused a significant increase in cardiac output and systemic blood pressure (67%+/-15%, p = 0.01; and 17%+/-7%, p = 0.04, respectively), as well as a decrease in central venous pressure by 49%+/-8% (p = 0.0001).

CONCLUSIONS

Heart displacement causes hemodynamic instability mainly by right heart dysfunction. The Enabler significantly stabilized circulation during vertical displacement of the beating heart.