Physiology of nonpulsatile circulation: acute versus chronic support.

Mammals seem to be able to adapt to nonpulsatile circulation. For chronic support, pressure and flow, not the presence of a pulse, are the major requirements to sustain normal organ function. Pulsatile flow, however, seems to offer advantages over nonpulsatile flow for acute support in maintaining lymphatic flow, decreasing systemic vascular resistance, improving peripheral and pulmonary capillary perfusion, and reversing shock. These advantages may not be seen with chronic support with adaptation to nonpulsatile flow.

Influence of ascending versus descending balloon counterpulsation on bypass graft blood flow.

BACKGROUND: Mechanical circulatory assistance is frequently needed in postcardiotomy patients to support the failing heart. A balloon catheter called SupraCor (ABIOMED Cardiovascular, Inc, Danvers, MA) has been developed and is similar to the existing intraaortic balloon pump with the exception of placement in the ascending versus the descending thoracic aorta. This investigation compared the effects of SupraCor versus standard intraaortic balloon pump on internal mammary artery and venous conduit bypass graft blood flow. METHODS: Porcine total heart bypass was used to anastomose a jugular vein from the ascending aorta to a subsequently ligated left anterior descending coronary artery. The left internal mammary artery was then anastomosed to the jugular vein so each conduit perfused the same coronary vascular bed. An additional right heart bypass preparation allowed precise control of cardiac output and blood pressure, which were maintained constant throughout mechanical circulatory assistance. Electromagnetic flow probes measured flow through each bypass graft and the other conduit was atraumatically occluded. RESULTS: The SupraCor caused a significant increase in both internal mammary artery (+70% from 35 +/- mL/min to 56 +/- 9 mL/min; p = 0.04) and venous bypass graft blood flow (+49% from 66 +/- 12 mL/min to 95 +/- 15 mL/min; p = 0.02) when compared with controls. The intraaortic balloon pump failed to alter internal mammary artery or venous bypass graft flow. CONCLUSIONS: The results demonstrate that counterpulsation with an ascending aortic balloon significantly increases coronary bypass graft flow in both internal mammary artery and venous conduits. In contrast, counterpulsation with a descending aortic balloon did not alter coronary bypass graft flow.

Left ventricular apical cannulation for circulatory support.

Circulatory support is occasionally needed for postcardiotomy low output. The left atrium may not be accessible for inflow cannulation. This article describes cannulation of the left ventricular apex for circulatory support.

Late tamponade with mechanical circulatory support.

BACKGROUND: Circulatory support with mechanical devices often leads to bleeding and tamponade. METHODS: We report a series of three patients that required mechanical circulatory support for postcardiotomy ventricular dysfunction. RESULTS: Late tamponade occurred in each patient with different clinical presentations. Early postoperative bleeding occurred in 2 patients. There was no active bleeding in any of the 3 patients. Transesophageal echocardiography was not helpful in making the diagnosis. CONCLUSION: Late tamponade, which may be the result of hematoma with earlier bleeding, can present as dyspnea, hypoxia, or forms of hemodynamic collapse. Exploratory media sternotomy is required to definitively make the diagnosis and to evacuate the hematoma.

Minimally invasive thoracoscopically assisted coronary artery bypass surgery.

OBJECTIVE: Minimally invasive techniques have been widely used in other surgical fields including video-assisted thoracic surgery (VATS) in thoracic surgery. These concepts are now being applied to cardiac surgery. The opportunities to make cardiac surgery less invasive include elimination of the median sternotomy incision, elimination of cardiopulmonary bypass and no manipulation of the aorta. MATERIALS AND METHODS: From January 1992 through September 1996, various aspects of minimally invasive cardiac surgery have been examined in the inanimate endoscopic trainer, animal model, human cadaver and in human clinical studies. Techniques of endoscopic sutured anastomosis as well as alternatives to suturing were first perfected in the inanimate trainer. Twenty animals then underwent endoscopic coronary artery bypass using the left internal mammary artery to the left anterior descending with circulatory support from an axial flow pump. Fifty eight minimally invasive coronary artery bypass procedures have been performed in humans using thoracoscopic assistance for internal mammary artery harvest. RESULTS: One hundred fifty endoscopic coronary anastomoses were performed in the inanimate trainer with the endoscopic suturing technique being the preferred method. Time required to perform an anastomosis decreased from greater than 60 min to a mean of 20 min as technique and instruments were developed. In animals, methods of access as well as enabling surgical instruments to allow crossclamp of the aorta and performance of the anastomosis were developed. Fifty-eight humans underwent coronary artery bypass using the left internal mammary artery placed to the left anterior descending under direct vision through a limited anterior thoracotomy on a beating heart. The procedure was successful in 52 patients with conversions required in six patients. Techniques were developed for immobilization for performance of the anastomosis. DISCUSSION: The ability to perform an endoscopic anastomosis still remains the rate limiting step for totally endoscopic coronary artery bypass surgery. The present MIDCAB (minimally invasive direct coronary artery bypass grafting) procedure is a significant advance in cardiac surgery, but still has limitations that make performance of an exact anastomosis still somewhat difficult and applicable only to single-vessel disease. Present efforts are directed toward extending the MIDCAB procedure by various immobilization and circulatory support devices and combining the MIDCAB procedure with catheter techniques for treating more advanced disease.

Temporary mechanical support with the BVS 5000 assist device during treatment of acute myocarditis.

BACKGROUND: Ventricular support with the BVS 5000 (Abiomed) has been used as temporary circulatory assist for the failing heart. Our purpose is to summarize four cases illustrating the role of mechanical unloading in acute myocarditis. METHODS: Four patients aged 16- to 33-year old presented with congestive heart failure 4 to 20 days after a flu-like syndrome. All patients were in severe cardiogenic shock +/- renal and liver dysfunction. Ejection fraction ranged from 5% to 26%. Indications for ventricular assist were failure of maximal medical treatment with > or = two inotropes +/- intra-aortic balloon pump. Myocardial biopsy revealed acute myocarditis in three patients and severe edema in one despite a characteristic clinical course. Two patients received immunotherapy with OKT3. Biventricular assist was used in three patients and left ventricular assist only was used in one. Mean support time was 8.3 days (7 to 11). RESULTS: All patients had recovery of myocardial function and were discharged from the hospital in good condition. CONCLUSION: The BVS 5000 device provides a safe, simple, and effective method to support the circulation during acute myocarditis. We hypothesize that this may facilitate myocardial recovery by decompressing the distended ventricle. Ventricular assist devices should be used early in the presence of hemodynamic deterioration on maximal medical therapy.

Influence of milrinone and norepinephrine on blood flow in canine internal mammary artery grafts.

BACKGROUND: Vasoactive agents are frequently needed in patients undergoing myocardial revascularization. The purpose of this study was to examine blood flow in the internal mammary artery (IMA) during infusion of drugs that are commonly used after myocardial revascularization. METHODS: A canine right heart bypass preparation allowed precise control of cardiac output and blood pressure, which were maintained constant during drug infusion to isolate the effect of the drug on the IMA conduit. The IMA was anastomosed to a ligated left anterior descending coronary artery. Electromagnetic flow probes measured IMA graft flow. RESULTS: Norepinephrine (0.1 microgram.kg-1.min-1) alone and when combined with phentolamine (8:5 ratio) did not alter IMA flow. Milrinone increased IMA flow 33% +/- 9%, from 37 +/- 7 to 49 +/- 10 mL/min. All hemodynamic variables were unchanged. CONCLUSIONS: The results suggest that: (1) norepinephrine did not have a deleterious effect on IMA flow and (2) milrinone may be a useful drug in patients undergoing myocardial revascularization by increasing IMA blood flow.

Atrial cannulation for left ventricular assistance: superiority of the dome approach.

Successful left ventricular support is dependent on adequate inflow drainage. We describe atrial cannulation using the dome of the left atrium, which in our experience has resulted in excellent inflow drainage.

ABIOMED BVS 5000: experience and potential advantages.

BACKGROUND: The ABIOMED BVS 5000 is a two-chambered extracorporeal pulsatile assist device intended for temporary circulatory support. The Food and Drug Administration granted approval for the device for postcardiotomy patients in 1992. METHODS: A worldwide registry is maintained with the BVS 5000. Currently 500 patients have been entered into the registry. The majority of patients were postcardiotomy (53%) and required biventricular assist devices (65%). RESULTS: Postcardiotomy patients have had a 27% discharge rate compared with cardiomyopathy patients with a more than 40% discharge rate. Comparison at Baylor University Medical Center of the ABIOMED BVS 5000 with a nonpulsatile device demonstrated an improved wean rate (60% versus 47%, respectively) as well as discharge rate (27% versus 17%, respectively). CONCLUSIONS: A worldwide registry combined with the experience at Baylor University Medical Center demonstrates the capability of the BVS 5000 to support postcardiotomy patients. The device is safe, simple, and effective. In addition, the pulsatile nature of the circulatory support appears to offer advantages over other systems.

Postcardiotomy shock: clinical evaluation of the BVS 5000 Biventricular Support System.

This prospective trial evaluated the safety and efficacy of a new pulsatile, temporary ventricular assist device, the BVS 5000. Patients were eligible for treatment if they were hemodynamically unstable despite maximal pharmacologic and intraaortic balloon pump therapy, were free of concomitant complications, and were less than 6 hours from the first attempt to separate from cardiopulmonary bypass. Fifty-five postcardiotomy patients were enrolled; 31 met all selection criteria and the remainder failed to meet criteria (n = 15) or were not successfully supported (n = 9). The BVS 5000 effectively restored hemodynamics: Mean arterial pressure increased (77.1 +/- 8.0 mm Hg on-support versus 50.1 +/- 15.3 mm Hg presupport; p = 0.0001). Cardiac index increased (2.3 +/- 0.3 L.min-1.m-2 on-support versus 1.6 +/- 0.6 L.min-1.m-2 presupport; p = 0.0013). Left ventricular filling pressure decreased (11.9 +/- 4.5 mm Hg on-support versus 23.8 +/- 8.7 mm Hg presupport; p = 0.0030). The most frequent complication was bleeding in 42 patients (76%). Of the patients meeting all criteria, 17 (55%) were weaned from support and 9 (29%) were discharged. Survival was significantly influenced by presupport cardiac arrest events. Survival among patients not experiencing arrest was 47%. Eight patients are long-term survivors and were asymptomatic in New York Heart Association class I or II at 1-year follow-up. The BVS 5000 restored hemodynamics, permitted myocardial recovery, and improved survival in a group of patients who would have otherwise died.

Inhibition of human internal mammary artery contractions. An in vitro study of vasodilators.

The internal mammary artery is currently the preferred conduit for myocardial revascularization; however, perioperative vasospasm of the internal mammary artery may limit its use as a bypass graft. The ability of various vasodilators to inhibit internal mammary artery contraction was investigated with the use of discarded segments of human internal mammary artery not used in coronary artery bypass grafting. Ring segments of human internal mammary arteries were suspended on strain gauges in muscle baths containing 37 degrees C Krebs solution for measurement of isometric tension in vitro. Arterial contraction was stimulated by elevating the extracellular potassium concentration to 70 mmol/L or by exposure to a 10 mumol/L concentration of norepinephrine, and inhibition of contraction by vasodilators was measured. The order of potency to inhibit potassium-induced contraction was as follows: nifedipine > verapamil > nitroprusside > papaverine. At maximal effective doses, nifedipine, verapamil, and papaverine almost completely inhibited potassium-induced contraction, whereas nitroprusside inhibited contraction by only 55%. When norepinephrine was used to contract the arteries, a biphasic relaxation curve was seen with nifedipine, but not with other vasodilator drugs. The order of potency to inhibit norepinephrine-induced contraction was as follows: nifedipine > nitroprusside > verapamil > papaverine. Maximal inhibition of norepinephrine contraction by these vasodilators ranged from 68% to 95%. Nitroglycerin, isoproterenol, and adenosine produced little or no inhibition of internal mammary artery contraction caused by potassium or norepinephrine. Although nifedipine was the most potent vasodilator, papaverine produced the greatest maximal inhibition of both potassium- and norepinephrine-induced contraction of human internal mammary artery.

Reversal of acute fulminant lymphocytic myocarditis with combined technology of OKT3 monoclonal antibody and mechanical circulatory support.

Reported is a case of acute fulminant lymphocytic myocarditis with profound circulatory compromise that was successfully reversed by treatment with OKT3 monoclonal antibody. The patient was supported with biventricular assist devices while being treated with the monoclonal antibody. The patient had remarkable recovery of ventricular function, which allowed for the removal of the device after 8 days of support. This case shows the success of combined technologies of monoclonal antibody and mechanical circulatory support to treat a potentially fatal disease process.

Calcification of porcine valves: a successful new method of antimineralization.

Despite distinct advantages over mechanical cardiac valve prostheses, the use of bioprosthetic valves remains limited due to poor long-term durability, primarily as a result of tissue calcification. A novel anticalcification process, based on treatment of porcine bioprostheses with a derivative of oleic acid, has been developed by one of us (J.M.G.) (US Patent Number 4,976,733). This process employing 2-aminooleic acid (AOA) was tested in a juvenile sheep model. Terminal studies after a 20-week interval included hemodynamic, radiographic, morphologic, and quantitative tissue calcium analyses. All control valves (n = 4) had thickened, immobile, heavily calcified leaflets, whereas all AOA-treated valves (n = 8) were pliable and free of calcium deposits. Calculated valve orifice areas for controls (0.9 +/- 0.2 cm2) (mean +/- standard error of the mean) was less than for AOA-treated valves (2.0 +/- 0.3 cm2) (p less than 0.05). Radiographic calcification scores were greatly elevated in the control (25.5 +/- 5.6) versus AOA-treated valves (0.5 +/- 0.5) (p less than 0.002). In quantitative mineralization studies, the mean calcium content of the control leaflets was 129 +/- 21 milligrams per gram dry weight cusp tissue versus 7.7 +/- 5.8 mg/g for AOA-treated valves (p less than 0.001). Pathologic examination confirmed heavy calcification in the control leaflets, which was essentially absent in the AOA-treated leaflets. However, cuspal hematomas in areas of structural loosening and surface roughening were noted in AOA-treated valves. This anticalcification process dramatically reduced mineralization of porcine valve prostheses in this model.

Vasodilator drug effects on internal mammary artery and saphenous vein grafts.

The internal mammary artery is a dynamic conduit used for myocardial revascularization in which potential exists for spasm as well as for vasodilation. This study investigated vasodilator drug effects on the mammary artery using nitroprusside and nitroglycerin in vitro to measure the inhibition of contraction of human internal mammary artery and in vivo to examine blood flow through a canine mammary artery. In the in vitro study, ring segments of human internal mammary arteries were suspended on strain gauges in muscle baths containing 37 degrees C Krebs solution for measurement of isometric tension in vitro. Arterial contraction was stimulated with 70 mM potassium and 10 microM norepinephrine, and inhibition of contraction by vasodilators was measured. Nitroprusside was more potent and effective than was nitroglycerin in inhibiting potassium and norepinephrine contraction. The in vivo study utilized a canine (n = 8) right heart bypass preparation that allowed precise control of cardiac output, blood pressure and heart rate, which were maintained constant. The internal mammary artery graft and the saphenous vein graft perfused the same coronary artery bed. Electromagnetic flow probes measured graft flow (with the other graft occluded) before and after 15 min of drug infusion (1 microgram/kg per min). Nitroglycerin significantly increased mammary artery flow 36 +/- 13%, whereas nitroprusside significantly decreased it 12 +/- 2%. Saphenous vein grafts responded differently; graft blood flow decreased with nitroglycerin and increased with nitroprusside. Thus, although nitroprusside was more effective than nitroglycerin in inhibiting mammary artery contraction in vitro, it decreased internal mammary artery graft flow measured in vivo. Nitroglycerin had the opposite effect, increasing mammary graft flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of minoxidil on myocardial hemodynamics, regional blood flow, and morphology in beagle dogs.

Studies were made of the effects of two doses of minoxidil (3 mg/kg), given 24 hours apart, on cardiovascular hemodynamics, regional myocardial blood flow, and cardiac morphology in beagle dogs. Minoxidil caused increases in mean right atrial and left ventricular end-diastolic pressure. Systemic and pulmonary vascular resistance were reduced; cardiac output was increased. Left ventricular stroke work and the systolic pressure time index were unchanged by monoxidil administration. The diastolic pressure time index and ratio of diastolic/systolic pressure time index were decreased by minoxidil. Regional myocardial blood flow, measured with radioactive microspheres, increased in all regions of the heart except to the left ventricular papillary muscles. Minoxidil increased blood flow to left ventricular subendocardial tissue; however, this increase was significantly less than that observed in corresponding areas of subepicardial tissue, thus reducing the subendocardial/subepicardial tissue blood flow ratio. These results suggest that minoxidil is an effective peripheral vasodilator but may result in inadequate subendocardial perfusion. Morphologic studies disclosed two types of minoxidil-induced cardiac lesions: left ventricular papillary muscle necroses, and hemorrhagic lesions which were most prominent in right atrium and were associated with inflammation, intramural hemorrhage, and fibrinoid necrosis of small arteries. The papillary muscle necrosis were attributed to hypoxia. The atrial lesions were not of ischemic or hypoxic origin, because minoxidil did not decrease blood flow to atrial tissue. It is suggested that the atrial lesions are related to excessive vasodilation.

Simultaneous repair of severe pectus excavatum and aortic valve replacement following previous open-heart surgery.

A 60-year-old man with a severe degree of pectus excavatum and previous coronary artery surgery required aortic valve replacement. At operation the sternal wires were found to be densely adherent to the aortic wall. We describe the surgical technique, which was carried out uneventfully.

Circulatory support for right ventricular dysfunction.

New modes of circulatory support for right ventricular dysfunction have recently been described. The present study compared the effectiveness of pulmonary artery balloon counterpulsation with a right ventricular assist device for support of surgically induced right ventricular dysfunction. Right ventricular hypertrophy was created in 16 neonatal lambs by pulmonary artery banding. Right ventricular dysfunction was produced in all animals by performing a right ventriculotomy and maintaining the pulmonary artery band. Four unassisted animals developed severe acute right heart failure and died. Six sheep had pulmonary artery balloon counterpulsation with a Dacron graft anastomosed to the proximal pulmonary artery as a reservoir for a 40 ml intra-aortic balloon after the onset of heart failure. The remaining six sheep had a pneumatically activated ventricular assist device inserted between the proximal pulmonary artery and the right ventricular apex. Periods of circulatory support with the balloon pump and the assist device on and off were compared. Decreases in right atrial pressure were observed with both balloon counterpulsation and right ventricular assistance: 14 +/- 1 to 11 +/- 1 mm Hg, p less than 0.0001, versus 19 +/- 2 to 12 +/- 2 mm Hg, p less than 0.0002, respectively. Cardiac output increased with both balloon counterpulsation and ventricular assistance: 1.45 +/- 0.16 to 2.03 +/- 0.13 L/min, p less than 0.001, versus 0.72 +/- 0.15 to 2.24 +/- 0.23 L/min, p less than 0.0002, respectively. Aortic systolic pressure increased in both support groups: 78 +/- 7 to 99 +/- 6 mm Hg, p less than 0.0004, versus 53 +/- 9 to 85 +/- 9 mm Hg, p less than 0.0001, respectively. Ventricular assistance produced greater changes in the right atrial pressure (39% +/- 6% versus 17% +/- 3%, p less than 0.01), cardiac output (153% +/- 39% versus 54% +/- 11%, p less than 0.05), and aortic systolic pressure (85% +/- 13% versus 39% +/- 9%, p less than 0.01). The insertion of a right ventricular assist device caused a significant increment in right ventricular dysfunction. These data, obtained with the devices in place but not operating, showed significantly increased right atrial and right ventricular end-diastolic pressures and approximately 50% less cardiac output than with the pulmonary artery balloon counterpulsation system. The results demonstrate that both modes of circulatory support were effective in reversing surgically induced right ventricular failure.(ABSTRACT TRUNCATED AT 400 WORDS)