Evaluation of floating impeller phenomena in a Gyro centrifugal pump.

The Gyro centrifugal pump developed as a totally implantable artificial heart was designed with a free impeller, in which the rotational shaft (male bearing) of the impeller was completely separated from the female bearing. For this type of pump, it is very important to keep the proper magnet balance (impeller-magnet and actuator-magnet) in order to prevent thrombus formation and/or bearing wear. When the magnet balance is not proper, the impeller is jerked down into the bottom bearing. On the other hand, if magnet balance is proper, the impeller lifted off the bottom of the pump housing within a certain range of pumping conditions. In this study, this floating phenomenon was investigated in detail. The floating phenomenon was proved by observation of the impeller behavior using a transparent acrylic pump. The impeller floating phenomenon was mapped on a pump performance curve. The impeller floating phenomenon is affected by the magnet-magnet coupling distance and rotational speed of the impeller. In order to keep the proper magnet balance and to maintain the impeller floating phenomenon at the driving condition of right and left pump, the magnet-magnet coupling distance was altered by a spacer which was installed between the pump and actuator. It became clear that the same pump could handle different conditions (right and left ventricular assist), by just changing the thickness of the spacer. When magnet balance is proper, the floating impeller phenomenon occurs automatically in response to the impeller rev. It is called "the dynamic RPM suspension".

[Partial anomalous pulmonary venous connection to the high portion of the superior vena cava associated with ventricular septal defect repaired with williams method using right atrial flap: report of a case].

A 3-year-old boy suffered from the poor body weight gain under the diagnosis of partial anomalous pulmonary venous connection (PAPVC) to the high portion of the superior vena cava (SVC) associated with ventricular septal defect (VSD) and intact atrial septum (IAS). Preoperative cardiac catheterization revealed the pulmonary to systemic flow ratio 2.6 and mean pulmonary arterial pressure of 21 mmHg. He successfully underwent surgical repair with Williams method using right atrial (RA) flap out and VSD patch closure. Postoperative course was uneventful and echocardiography demonstrated no obstruction at the both routes of neo-SVC and neo-right upper pulmonary venous return.

[Aortic valve replacement for the patient with Osler-Rendu-Weber disease].

Osler Rendu-Weber (O-R W) disease (hereditary haemorrhagic telangiectasia) is characterized by an anormality of the peripheral blood vessels which often causes recurrent epistaxis. We presented a case of aortic valve replacement for the patient with O-R-W disease. A 75-year-old woman diagnosed as O-R-W disease with chest pain and dyspnea was admitted. Preoperative transthoratic echocardiography showed severe aortic valve stenosis (AS) with a pressure gradient (from left ventricle to ascending aorta) of 72.5 mmHg. Urgent aortic valve replacement (AVR) was performed after preoperative hormonal (estrogen-progesterone) therapy, that might be effective for bleeding from vascular ectasia. No hemorrhagic tendency was recognized and the postoperative course was uneventful.

Current status on the development of a totally implantable biventricular assist device: the Baylor Gyro BVAD.

OBJECTIVE: The Baylor Gyro BVAD is under development with the final goal of establishing a totally implantable biventricular assist system (BVAD). The aim of this study was to evaluate the safety, reliability, and effectiveness of the device in a long-term in vivo model. METHODS: The BVAD was implanted into eight calves for longer than 4 weeks in a biventricular bypass fashion, with the native heart remaining. Pump performance was assessed with the system's digital data acquisition unit. Postoperatively, anticoagulation was maintained with i.v. heparin perfusion (ACT< or = 250 sec) gradually replaced by coumadin. Treadmill exercise tests were performed daily following a 10-day reconvalescence period after surgery. RESULTS: The animals were kept alive for 37-90 days. The pumps yielded average flows of 5.3 +/- 1.1 l/min and 4.9 +/- 0.7 l/min for the LVAD and RVAD, respectively. Power consumption was 8.2 +/- 2.7 W and 9.6 +/- 4.7 W at 1935 +/- 123 rpm and 2015 +/- 365 rpm, respectively. All cases exhibited low hemolysis; renal and liver function were kept normal throughout the experiments. The animals demonstrated no thromboembolic neurological symptoms and tolerated moderate treadmill exercise. CONCLUSION: The Baylor Gyro BVAD demonstrated effective and reliable in vivo performance with acceptable biocompatibility. Based on these studies, we conclude that the system will be suitable as a long-term totally implantable BVAD for uses intended for longer than two years.

Evaluation of floating impeller phenomena in a gyro centrifugal pump.

The Gyro centrifugal pump, developed as a totally implantable artificial heart, was designed with a free impeller in which the rotational shaft (male bearing) of the impeller was completely separated from the female bearing. For this type of pump, it is very important to keep the proper magnet balance (impeller-magnet and actuator-magnet balance) to prevent thrombus formation or bearing wear. When the magnet balance is not proper, the impeller is jerked down into the bottom bearing. On the other hand, if magnet balance is proper, the impeller is lifted off the bottom of the pump housing within a certain range of pumping conditions. In this study, this floating phenomenon was investigated in detail. The floating phenomenon was proven by observation of the impeller behavior by means of a transparent acrylic pump. The impeller floating phenomenon was mapped on a pump performance curve. The impeller floating phenomenon is affected by the magnet-magnet coupling distance and the rotational speed of the impeller. To keep the proper magnet balance and to maintain the impeller floating phenomenon at the driving conditions of right and left pumps, the magnet-magnet coupling distance was altered by a spacer that was installed between the pump and actuator. It became clear that the same pump could handle different conditions (right and left ventricular assist) by changing the thickness of the spacer. When magnet balance is proper, the floating impeller phenomenon occurs automatically in response to the impeller revolution. This is called "the dynamic revolutions per minute suspension."

[Off-pump versus standard on-pump reoperative coronary artery bypass grafting].

BACKGROUND: Using standard on-pump procedures, repeat coronary artery bypass grafting (re-CABGs) are associated with a higher morbidity and mortality than first-time CABGs. This retrospective study assessed the clinical outcomes of off-pump re-CABG versus on-pump re-CABG. METHODS: From 1983, 2nd CABG and 3rd CABGs were performed in 162 patients at our institute. The early and late results of 142 patients who received standard on-pump re-CABGs and 20 patients who received off-pump re-CABGs were evaluated. The 2 groups were similar in age, sex, preoperative ejection fraction (EF) and number of coronary lesions. However, mean number of distal anastomoses per patient was significantly higher in on-pump (2.0 +/- 0.8) than in off-pump re-CABG (1.4 +/- 0.6) [p = 0.0009]. RESULTS: Hospital mortality tended to be higher in the on-pump group (5.6%) than in the off-pump group (0%) [p = 0.6]. Morbidity in term of total postoperative complications tended to be higher for on-pump (14.1%) than in off-pump (0%) [p = 0.14]. The 5-year survival rate tended to be higher in the off-pump group (100%) than in the on-pump group (80.8 +/- 3.5%) [p = 0.096]. CONCLUSIONS: In selected patients, off-pump re-CABG can be a reliable and safe option. The mid-term survival and event-free survival rates achievable with the off-pump option are encouraging.

Operating point control system for a continuous flow artificial heart: in vitro study.

We proposed and developed a practical and effective servo control system for rotary blood pumps. A rotary blood pump for assisting the failing natural heart should be operated only in physiologically acceptable conditions. The operation of a rotary blood pump is based on the rotational speed of the impeller and pressure head. If the pump flow and the pressure head are set within an acceptable range, the driving condition is deemed normal condition, and this control system maintains the preset operating point by applying proportional and detective control (PD control). If the pump flow or pressure head is outside the acceptable range, the driving condition is determined to be abnormal condition, and this system operates the pump in a recovery fashion. If the driving condition is kept under abnormal conditions of sudden decrease of the flow, the condition is termed a suction condition. The controller releases the pump from the suction condition and later returns it to the normal condition. In this study, we evaluated these servo control modes of the centrifugal pump and confirmed whether the performance of this proposed operating point control system was practical.

[Severe tricuspid regurgitation late after aortic and mitral double valve replacement; report of a case].

A 59-year-old man had undergone aortic and mitral valve replacement (DVR) for rheumatic aortic and mitral valve stenosis 15 years ago. At that time, echocardiography did not detect tricuspid regurgitation (TR), and catheterization data showed right atrial pressure v wave of 8 mmHg and pulmonary artery pressure of 27/12 (17) mmHg. One year after DVR, hepatomegaly and jugular venous dilatation appeared, and after 5 years edema of both legs became apparent. After 7 years, chest X-ray showed an increase of cardio-thoracic ratio, and for the first time, echocardiography detected mild TR. Fifteen years after DVR, severe general fatigue, shortness of breath and hepatomegaly could not be controlled with medication. Catheterization data showed right atrial pressure v wave of 23 mmHg and pulmonary artery pressure of 28/13 (17) mmHg. Right ventriculography showed progression of severe TR. Tricuspid valve replacement (TVR) was performed using a St. Jude Medical 31 M mechanical valve under natural cooling and heart beating. The tricuspid valve was only slightly thickened and no subvalvular abnormalities were seen other than a severely dilated tricuspid annulus. Postoperative course was uneventful and he was discharged 44 days after the TVR. He is currently doing well 6 years after the TVR. All terms, he did not have pulmonary hypertension or left-side heart problems. We suspect that the cause of TR was not secondary, and was included in the category of isolated TR. If the left heart is completely treated, as in this case, it is important to follow-up for signs of right heart failure, before TR is detected.

Development of the Baylor Gyro permanently implantable centrifugal blood pump as a biventricular assist device.

The Baylor Gyro permanently implantable centrifugal blood pump (Gyro PI pump) has been under development since 1995 at Baylor College of Medicine. Excellent results were achieved as a left ventricular assist device (LVAD) with survival up to 284 days. Based on these results, we are now focusing on the development of a biventricular assist device (BVAD) system, which requires 2 pumps to be implanted simultaneously in the preperitoneal space. Our hypothesis was that the Gyro PI pump would be an appropriate device for an implantable BVAD system. The Gyro PI 700 pump is fabricated from titanium alloy and has a 25 ml priming volume, pump weight of 204 g, height of 45 mm, and pump diameter of 65 mm. This pump can provide 5 L/min against 100 mm Hg at 2,000 rpm. In this study, 6 half-Dexter healthy calves have been used as the experimental model. The right pump was applied between the infundibular of the right ventricle and the main pulmonary artery. The left pump was applied between the apex of the left ventricle and the thoracic descending aorta. As for anticoagulation, heparin was administered at the first postoperative week and then converted to warfarin sodium from the second week after surgery. Both pump flow rates were controlled maintaining a pulmonary arterial flow of less than 160 ml/kg/min for the sake of avoidance of pulmonary congestion. Blood sampling was done to assess visceral organ function, and the data regarding pump performance were collected. After encountering the endpoint, which the study could not keep for any reasons, necropsy and histopathological examinations were performed. The first 2 cases were terminated within 1 week. Deterioration of the pump flow due to suction phenomenon was recognized in both cases. To avoid the suction phenomenon, a flexible conduit attached on the inlet conduit was designed and implanted. After using the flexible inflow conduit, the required power and the rotational speed were reduced. Furthermore, the suction phenomenon was not observed except for 1 case. There was no deterioration regarding visceral organ function, and pulmonary function was maintained within normal range except for 1 case. Even though the experimental animal survived up to 45 days with the flexible inflow conduit, an increase in power consumption due to thrombus formation behind the impeller became a problem. Lower rotational speed, which was probably produced by the effectiveness of the flexible inflow conduit, was speculated to be one of the reasons. And the minimum range of rotational speed was 1,950 rpm in these 6 BVAD cases and the previous 3 cases of LVAD. In conclusion, 6 cases of BVAD implantation were performed as in vivo animal studies and were observed up to 45 days. The flexible inflow conduit was applied in 4 of 6 cases, and it was effective in avoiding a suction phenomenon. The proper rotational speed of the Gyro PI 700 pump was detected from the viewpoint of antithrombogenicity, which is more than 1,950 rpm.

[A case report of primary cardiac leiomyosarcoma].

A 26-year-old woman presenting symptoms of rapid progressive heart failure consulted with our hospital. Two-dimensional echocardiography showed a large mass in the left atrium (LA) and severe pulmonary hypertension. Emergent operation was performed because of hemodynamic reason and the risk of embolism. The tumor (7 x 6 x 3 cm) which was lobulated and had a smooth surface was arising from posterior wall of LA extending into the ostium of right lower pulmonary vein. The portion of tumor located was excised. The defect was reconstructed by bovine pericardium. Postoperative histopathological diagnosis was leiomyosarcoma. Hemodynamics recovered after surgical treatment and there were no problems for 5 months. However, tumor recurrence in LA and pulmonary metastasis was found 5.5 months after surgery. The patient died two weeks later by progressive heart failure. Primary cardiac leiomyosarcoma is extremely rare. The current world literature is reviewed with respect to this rare tumor.

[A tube retractor for cardiac surgery].

A retractor exclusively used to retract the tubes in cardiac surgery which needs cardiopulmonary bypass was developed. The half-cylinder-shaped end, the lightly curved handle and the flat and triangular grip enable easy and effective grasp of the tubes. This new instrument facilitates operative procedures by effectively retracting the tubes which persistently obstruct the operative field, in such a case of placement of a retrograde cardioplegia tube via the right atrium.

[Recovery of left ventricular function after mitral valve replacement for chronic mitral regurgitation: optimal timing of operation according to long-term recovery].

OBJECTIVES: Surgical outcome for mitral regurgitation has significantly improved in recent years, so consideration of the optimal operative timing to achieve long-term quality of life for the patients has become more important. Preoperative indices that predict postoperative left ventricular function are very important for decision of the operative timing. To reassess the optimal operative timing for mitral regurgitation, long-term recovery of the postoperative left ventricular function was correlated with preoperative left ventricular end-systolic volume index(LVESVI). METHODS: One hundred eighty-two patients with mitral regurgitation underwent standard mitral valve replacement between January 1973 and June 1993. The patients were divided into 3 groups according to the preoperative LVESVI: Group I (LVESVI > or = 100 ml/m2) included 23 patients, Group II (60 < or = LVESVI < 100 ml/m2) 81 patients and Group III (LVESVI < 60 ml/m2) 78 patients. Two-dimensional echocardiography was performed to measure left ventricular diastolic dimension, systolic dimension, fractional shortening, end-systolic wall stress and mass index before operation(pre), and 1 month(early) and 3 years(late) after the operation. RESULTS: Left ventricular diastolic dimension in each group decreased in the early period, but Group I returned to the abnormal range in the late period. Left ventricular systolic dimension in Groups I and II was at the upper limit of the normal range in the early period and returned to the abnormal range in the late period, but Group III remained within the normal range throughout the study. Fractional shortening in all groups decreased to the abnormal range in the early period, but only Group III returned to the normal range in the late period. End-systolic wall stress in Group I tended to increase, but Group II had no change, and Group III returned to the normal range during the early and late periods. Mass index in Groups I and II remained within the abnormal range, but Group III returned to the normal range in the late period. CONCLUSIONS: Long-term recovery of the left ventricular function in Group I showed a continuous deterioration due to irreversible change of the left ventricular myocardium and Group II showed no significant change. In contrast, Group III demonstrated a significant improvement after standard mitral valve replacement. Patients with preoperative LVESVI of more than 100 ml/m2 have already lost the optimal timing for surgical treatment of mitral regurgitation.

[Late results of SJM and CM valves in bentall procedure].

Recently, Bentall procedure is commonly performed for annuloaortic ectasia with aortic regurgitation or dissecting aneurysm. And the operative results are improving. In this study, we evaluated results of the St. Jude Medical (SJM) and Carbomedics (CM) valves which were used in this procedure. From 1979 to 1994, 87 SJM valves and 22 CM valves were implanted in the aortic position of Bentall procedure. Total follow-up was 528.6 years in the SJM group and 56.5 years in the CM group. According to the Kaplan-Meier actuarial method and the Cox-Mantel statistical analysis, actuarial survival, thromboembolism free rate, reoperation free rate, event free rate were not different between the SJM and CM groups. These results suggest that, current selection of the SJM and CM valves would be acceptable in Bentall procedure.

[Efficacy of terminal warm blood cardioplegia in combination with Bretschneider-HTK solution for myocardial protection].

Many reports indicated that terminal warm blood cardioplegia (TWBC) was useful for reduction of the reperfusion injury in cardiac operations. We introduced Bretschneider-HTK solution (B-HTK) from April 1992, and combined use of the TWBC and the B-HTK was performed from May 1996. The purpose of this study was to evaluate clinical efficacy of the TWBC in combination with B-HTK for myocardial protection. In patient with valve operations from May 1995 to May 1997, clinical results were compared between the B-HTK with TWBC group (34 patients) and the B-HTK alone group (37 patients). Between two groups, there was no significant difference in patient characteristics, preoperative NYHA class, cardiopulmonary bypass time, aortic cross clamp time, minimum rectal temperature, rewarming and circulatory support time, incidence of IABP and blood concentration of max CPK, max GOT. Furthermore, the cardiac index in 1 postoperative day showed some trend to be higher in the combined TWBC group than that in the B-HTK alone group. But there was no significant difference between two groups in the LV shortening fraction at 14 postoperative day. Incidence of DC defibrillation was significantly lower in the combined TWBC group than that in the B-HTK alone group. These results suggested that combination of the TWBC might be useful for reduction of the reperfusion injury following myocardial protection with B-HTK solution.

[Aortic valve replacement with the Toronto stentless porcine valve in a patient with clipping for cerebral arterial aneurysm].

A 48-year-old man, who had a cerebral arterial aneurysm, was admitted in our institution for operation of aortic valve stenosis. At first, he underwent clipping for cerebral arterial aneurysm under precise management of his hemodynamic condition. After the clipping operation, we performed aortic valve replacement with the Toronto stentless porcine valve because no anticoagulant therapy was ideal for patient with cerebrovascular disease and larger effective orifice area was preferable for stenotic aortic annulus. By means of echocardiography, mean pressure gradient of the aoric valve decreased from 42 mmHg to 22 mmHg after the valve operation. He was discharged from the hospital on the 23rd postoperative day, and he has been doing well without thromboembolic events and bleeding complications for five postoperative months. This experience suggest that the Toronto stentless porcine valve might be one of the valve of choice for patients with aortic valve disease and cerebrovascular disease.

[Simultaneous tricuspid valve operation in patients undergoing aortic and mitral double valve replacement].

In triple valvular surgery, AVR+MVR+TVR or TVP, there are some problems around operation, because patients impaired cardiac function after a long history of the disease and some of them are reoperation cases. The sixty-five patients operated from May in 1980 to June in 1993 were examined. They were divided into two groups, group P and group R, depending upon procedure of tricuspid position. Group P consisted of 51 patients and group R of 14 patients. There were 22 (34%) reoperations. In group P, organic changes in tricuspid valve were mild, however in group R, there were commissural fusion in 8 patients, destruction of leaflet due to infectious endocarditis in one patient, and marked tricuspid annular dilatation in five patients. There was one early death in group R, no early death in group P. Actuarial survival rate at the 10th postoperative year was good as 81.6% in group P and 85.7% in group R. There were no significant differences in operative mortality and actuarial survival between group P and R.

[Open heart surgery without blood transfusion for complete atrioventricular septal defect associated with tetralogy of Fallot].

Open heart surgery without blood transfusion was successfully performed in two patients with complete atrioventricular septal defect associated with tetralogy of Fallot. The postoperative hemodynamics and respiratory status were uneventful in both patients (central venous pressure after ICU admission: 13.7 cmH2O and 11.5 cmH2O, intubation time after surgery: 9 hours and 11 hours). Autologous blood donation immediately after induction of anesthesia and minimization of bypass circuit were effective methods for open heart surgery without blood transfusion, particularly in cyanotic patients requiring prolonged cardiopulmonary bypass for intracardiac repair.

Effect of additional intraaortic balloon support during weaning from a left ventricular assist system.

A safe and reliable method of weaning from a left ventricular assist system (LVAS) is necessary for successful circulatory support in patients with marginal heart failure. The purpose of this study is to assess the effect of additional intraaortic balloon (IAB) support during weaning from an LVAS by means of the LV pressure-volume relationship. A pneumatic LVAS with a sac-type blood pump was implanted in six adult mongrel dogs weighing 14 to 20 kg. All dogs had a drainage cannula placed in the left atrium and an outflow conduit in the ascending aorta. Hemodynamic parameters, pulmonary arterial flow, and pump output were monitored. An IAB was inserted through the groin. A conductance catheter and microtip manometer were inserted into the LV cavity. As a combination driving mode, LVAS ejection in the early diastolic phase and IAB inflation in the late diastolic phase were applied. After evaluation of baseline LV function, the pressure-volume relationship was repeatedly measured during change of driving modes as isolated LVAS, LVAS + IAB (1:1), LVAS + IAB (2:1), and isolated IAB supports. Finally, LV failure was introduced by stepwise ligation of left coronary arteries, and the LV pressure-volume relationship was measured in each driving mode. Under normal conditions, the pressure-volume loop showed no significant change among the four driving modes. In contrast, the LV pressure-volume relationship significantly improved according to the degree of additional IAB support on LVAS assistance under the condition of LV failure. These results suggest that additional IAB support might improve LV energy during weaning from an LVAS.

[Successful surgical repair of atrial septal defect associated with mitral regurgitation and tricuspid regurgitation].

A 63-year-old woman with atrial septal defect, mitral regurgitation, and tricuspid regurgitation underwent mitral valvuloplasty with 30 mm Carpentier ring, patch closure of atrial septal defect and tricuspid annuloplasty with 36 mm Carpentier ring. She was doing well now. In this case, preoperative catheterization showed left-to-right shunt ratio of 32% and right-to-left shunt ratio of 51%. The existence of right-to-left shunt was considered to be related to the grade of tricuspid regurgitation. It is concluded that in these cases, surgical repair should be recommended before the onset of severe progressive heart failure.

[Saphenous vein to saphenous vein bypass grafting in four redo CABG patients].

In four redo CABG patients, new saphenous vein grafts were anastomosed to the angiographically normal part of the old, and partially narrowed or occluded saphenous vein grafts in an end-to-side fashion. Inner surface of the old saphenous vein was confirmed to be smooth and free of atherosclerotic change during anastomosis. Postoperative course was uneventful and angiography demonstrated the good patency of new saphenous vein grafts in all patients. Although this technique is not acceptable if the old saphenous vein graft shows extensive atherosclerotic change, this method may be a useful alternative in case of limited saphenous vein graft disease in terms of less difficulty and operation time.