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PubMedDate not supplied

Optimal timing for application of ventricular assist devices in patients who cannot be weaned from cardiopulmonary bypass. An experimental study.

Missing the moment for application of ventricular assist devices (VAD) may be one of the major causes of multiple organ failure in patients who are to be weaned from cardiopulmonary bypass (CPB) with the aid of VAD. To determine the optimal timing for application of VAD in such patients, we examined the effect of a CPB assist on cardiac functional recovery from severe global ischemia using an experimental canine system. In the present study we created myocardial ischemia by clamping the aorta for 20 minutes (Group I; N = 7) or 45 minutes (Group II; N = 11) under normothermic CPB. The reliability of the method in creating severe cardiac failure was confirmed by testing the levels of adenosine triphosphate (ATP), creatine phosphate (CP), and lactate. After reperfusion of the myocardium, the heart was assisted by a totally vented CPB. The left ventricular end-systolic pressure-volume relationship (Emax), which is a load-independent index of contractility, was obtained every 15 minutes for up to 120 minutes of reperfusion. The Emax revealed that the function of the damaged heart recovers exponentially with time after reperfusion. From curves of the functional recovery of the heart, CPB support appeared to be beneficial for the first 60 minutes after reperfusion, and aided in the recovery of cardiac function in hearts damaged by global myocardial ischemia. However, CPB assist thereafter may not be effective in further improving cardiac function. We therefore concluded that the decision to use VAD should be determined by cardiac function by 60 minutes of reperfusion to avoid prolonging CPB time.

Adenosine Triphosphate↗
PubMedDate not supplied

An electromagnetic pneumatic blood pump driver.

An electromagnetic pneumatic pump driver has been developed with the goals of enhanced mechanical reliability and simplicity of operation. The new driver eliminates failure prone components such as solenoid valves or pressure regulators common to conventional pneumatic drive systems, has only a single moving part, and provides for closed-loop operation in which stroke volume and dP/dT are controlled on each beat in real time. Power is provided by a high force (178 N) electromagnetic linear actuator. This assembly uses a high energy density neodymium-iron-boron permanent magnet, low loss vanadium alloy pole pieces, and an energized moving coil. The nominal stroke length of the actuator is 1.7 cm. During operation, the moving coil always remains within a fixed annular air gap, resulting in a measured force output versus applied power linearity of better than 92% over its stroke range. The coil is directly attached to the free end of a 10 cm diameter, 21 convolution, welded titanium metal bellows that forms the gas containing element of the system. The comparatively low pressure gradients across the bellows in this application result in a predicted life for the bellows in excess of 10(9) cycles. Bellows position and internal pressure are monitored continuously to control the pneumatic output. The linear actuator total excursion and velocity are adjusted on each beat using a closed-loop servo system. This results in a pump driver with no operator required adjustment of drive pressure. Instead, there are user selected settings of stroke volume, operating mode, and fill sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Assisted Circulation↗
PubMed1988

Biomaterial-associated calcification: pathology, mechanisms, and strategies for prevention.

Deposition of calcium-containing apatite mineral occurs widely in association with cardiovascular and noncardiovascular medical devices and biomaterials, is the leading cause of failure of contemporary bioprosthetic heart valves, and limits the functional lifetime of experimental (and potentially clinical) mechanical blood pumps and polymeric heart valves. Calcification of bioprosthetic tissue is primarily intrinsic, related to cuspal connective tissue cells and fragments, and collagen. In contrast, the predominant site of calcific crystals on flexing polymeric surfaces in blood pumps or valve prostheses is extrinsic, associated with adherent cells, thrombus, or pseudointima. Pathologic calcification shares key features with physiologic skeletal mineralization, including crystal initiation through the mediation of cell membranes, usually in the form of extracellular vesicles. This suggests a unified hypothesis for normal and abnormal mineralization. Several approaches are being studied experimentally for the inhibition of bioprosthetic heart valve calcification. Controlled-release diphosphonate therapy, perhaps in conjunction with an anticalcification cuspal pretreatment, appears most effective. Research objectives in biomaterial-associated calcification include (1) development of animal models, (2) determination of initial crystal nucleation events and sites, (3) elucidation of the relative roles of host, implant, and mechanical determinants, and (4) development of approaches for the inhibition of mineralization.

Assisted Circulation↗
PubMedDate not supplied

Bridge to heart transplantation: the Penn State experience.

At The Pennsylvania State University, we have performed four bridge-to-heart transplantation procedures in the past year. Two patients were supported with an LVAD, and two patients were supported with a TAH. One patient had a successful transplantation and remains well 10 months after operation; two patients died of sepsis after transplantation. A fourth patient has had a TAH in place for greater than 110 days and is currently awaiting transplantation. The problems that remain to be solved are developing strategies to minimize the risk of infection, defining the indications for use of an LVAD vs a BVAD vs a TAH, developing an effective regimen to prevent thromboembolism, and determining the proper interval for transplantation after the insertion of a mechanical pump as a bridge.

Adult↗
PubMed1988

Follow-up of survivors of mechanical circulatory support.

Improvements in mechanical support for profound circulatory collapse have resulted in increasing survival of these critically ill patients. Since 1980, 27 patients aged 3 days to 69 years (mean 34.9 years) who required mechanical circulatory assistance have been followed up after discharge from the hospital. The refractory cardiogenic shock necessitating mechanical support occurred postoperatively in 22 patients (coronary artery bypass in nine, valve replacement in four, correction of congenital heart defects in nine) and with end-stage cardiomyopathy in five. Fourteen patients were supported with a Pierce-Donachy ventricular assist device (left ventricular assist in seven, right ventricular assist in three, both in four); nine were supported with extracorporeal membrane oxygenation, two with a Medtronic centrifugal left ventricular assist pump, one with biventricular Biomedicus pumps, and one with a Novacor left ventricular assist system. The duration of support ranged from 8 hours to 91 days with a mean of 3.5 days in patients supported for postoperative shock. Major complications occurred in 18 patients (67%), including bleeding that necessitated operative exploration in 14, serious infection in five, renal failure in two, and stroke in two. The five patients with cardiomyopathy underwent cardiac transplantation. The remaining 22 patients who had postoperative cardiogenic shock were weaned from support. There have been four late deaths: two cardiac related at 6 months and two of cancer at 46 and 53 months (one patient was in New York Heart Association class I and the other in class II before death). The remaining 23 survivors have been followed up for 3 to 79 months (mean 29 months) and at last examination 17 (74%) were in class I, two (9%) were in class II, three (13%) were in class III, and one (4%) was in class IV. Eight patients are employed full time, three are retired, four attend school, three are in preschool, one is a housewife, and one is unemployed but free of symptoms. Only four patients have significant cardiac disability, and one of these still works. In conclusion, mechanical circulatory assistance allows adequate support to permit satisfactory long-term survival in patients with refractory cardiogenic shock.

Adult↗
PubMed1988

A portable pneumatic driving unit for a left ventricular assist device.

The authors developed a portable air driving unit for an artificial heart. As the portable energy source of the driver, a commercially available Ni-Cd battery was used. A linear compressor was selected as a portable size compressor. To reduce the number of parts to be assembled, a new type of pneumatic system was employed. In this system, the pressure level was regulated by varying the output flow rate of the compressor instead of using a pressure regulator and large air reservoirs. A one-board microcomputer and pressure sensors were used to control the pressure level. The total weight of the unit is 9.5 Kg. After assembling the components into the portable unit, a blood pump was connected to examine the output characteristics of the system. It was confirmed that the unit could drive the blood pump continuously for more than 2 hours under the following conditions: output flow rate of the blood pump = 5 L/min and output pressure = 100 mmHg.

Assisted Circulation↗
PubMed1987

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)

Animals↗
PubMed1987

Long-term results of ventricular assist pumping in postcardiotomy cardiogenic shock.

Short-term survival of patients who require ventricular assist pumping for postcardiotomy cardiogenic shock has been encouraging and has provided enough survivors to allow evaluation of long-term results. We observed nine survivors, 39 to 69 years of age (mean = 54.6) for 10 to 53 months (mean = 31) after their discharge from the hospital. In three patients, the angiographic ejection fraction was normal before the operation, whereas in six patients it was moderately to severely impaired. All nine patients were in New York Heart Association Functional Class IV before operation. After operation, eight of the nine patients were in Functional Class I or II. In the remaining patient, the ejection fraction fell markedly and the postoperative functional class remained unchanged. Two patients were employed full-time and one, part-time. Five patients were retired but active and had no cardiac disability, although two of the five did have residual partial noncardiac disability. The remaining patient, a housewife, continued to have compensated congestive heart failure but was relieved of angina. During the follow-up period, five of the nine patients died suddenly after 12, 18, 25, 30, and 38 months from causes that included pulmonary embolus and probable arrhythmias. Survivors who have had ventricular assist pumping for postcardiotomy cardiogenic shock have a good chance of resuming active lives. The risk of being a "cardiac cripple" is small, as is the risk of significant noncardiac disability.

Adult↗