Motor current waveforms as an index for evaluation of native cardiac function during left ventricular support with a centrifugal blood pump.

Control of ventricular assist devices (VADs) for native heart preservation should be attempted, and it could be one strategy for dealing with the shortage of donors in the future. In the application of a nonpulsatile blood pump for ventricular assistance from its apex to the aorta, the bypass flow and hence motor current of the pumps change in response to the ventricular pressure change. Utilizing these intrinsic characteristics of the continuous flow pumps, this study investigated whether or not motor current could be used as an index for continuous monitoring of native cardiac function. In Study 1, a centrifugal blood pump (CFP) VAD was installed between the apex and descending aorta of a mock circulatory loop. In this model, a baseline with a preload of 10 mm Hg, afterload of 40 mm Hg, and left ventricular (LV) systolic pressure of 40 mm Hg was used. The pump rpm were fixed at 1,300, 1,500, and 1,700, and LV systolic pressure was increased up to 140 mm Hg by a step of 20 mm Hg while observing the changes in LV pressure, motor current, pump flow, and aortic pressure. In Study 2, in vivo experiments were performed using 5 sheep. A left heart bypass model was created using a centrifugal pump from the ventricular apex to the descending aorta. The LV pressure was varied through administration of dopamine while observing the changes in LV pressure, pump flow, motor current, and aortic pressure at 1,500 and 1,700 rpm. An excellent correlation was observed both in vitro and in vivo studies in the relationship between motor current and LV pressure. In Study 1, the correlation coefficients were 0.77, 0.92, and 0.99 for 1,300, 1,500, and 1,700 rpm, respectively. In Study 2, they were 0.90 (Animal 1), 0.82 (Animal 2), 0.89 (Animal 3), 0.93 (Animal 4), and 0.70 (Animal 5) respectively for 1,500 rpm, and 0.94 (Animal 2), 0.85 (Animal 3), 0.94 (Animal 4), and 0.89 (Animal 5) respectively, for 1,700 rpm. The relationship between motor current and pump flow and LV pressure showed an unstable correlation in an in vivo study. These results suggest that motor current amplitude monitoring could be useful as an index for the control of VADs for native heart preservation.

Control strategy for rotary blood pumps.

The control strategy for ventricular support with a centrifugal blood pump was examined in this study. The control parameter was the pump rpm that determines pump flow. Optimum control of pump rpm that reflects the body's demand is important for long-term, effective, and safe circulatory support. Moreover, continuous, reliable monitoring of ventricular function will help successfully wean the patients from the ventricular assist device (VAD). The control strategy in this study includes determination of the target pump rpm that can provide the flow required by the body, fine-rpm-tuning to minimize deleterious effects such as suction in the ventricle, and assessment of ventricular function for successful weaning from VADs. To determine the target pump rpm, we proposed to use the relation between the native heart rate and cardiac output, and the relation between the pump rpm and centrifugal pump output. For fine-tuning of the pump rpm, the motor current waveform was used. We computed the power spectral density of the motor current waveform and calculated the ratio of the fundamental to the higher order components. When this ratio was larger than approximately 0.2, we assumed there would be a suction effect in the ventricle. As for assessment of ventricular function, we used the amplitude of the motor current waveform. The control system implemented using a DSP functioned properly in the mock circulatory loop as well as in acute animal experiments. The motor current also showed a good correlation with the ventricular pressure in acute animal experiments.

Changes in patterns of left ventricular hypertrophy after aortic valve replacement for aortic stenosis and regurgitation with St. Jude Medical cardiac valves.

In this study, we analyzed the extent and pattern of regression of left ventricular (LV) hypertrophy after aortic valve replacement in patients with aortic stenosis (AS) and compared the results with those of another group of patients with aortic regurgitation (AR). Seventy patients who underwent isolated aortic valve replacement were divided into 2 groups. Group 1 was comprised of 29 patients who underwent aortic valve replacement for aortic stenosis, and Group 2 of 41 patients who underwent aortic valve replacement for aortic regurgitation. A third group of 10 healthy subjects served as a healthy control group. Echocardiographic studies were done before the operation and 5 years postoperatively. At follow-up, a significant reduction in the left ventricular mass was found in both groups, but it remained significantly greater than in the healthy control group. The ratio of LV wall thickness to radius (th/r) in Group 1 decreased significantly, and at follow-up it was within the normal value. In Group 2, the th/r ratio increased, and at follow-up it was within the normal value. After aortic valve replacement, the wall thickness remained significantly greater than normal for patients with AS, and the chamber radius remained significantly greater than normal for patients with AR. For these reasons, LV hypertrophy still existed in both groups at postoperative follow-up. The actuarial survival rate was 85.3% at 16 years for Group 1 and 83.4% at 18 years for Group 2. There was no significant difference in the long-term survival rates between the 2 groups. Actuarial freedom from valve-related events was 91.9% at 16 years for Group 1 and 82% at 18 years for Group 2. There was no significant difference in the valve-related event free curves between groups. After 5 years of follow-up, th/r reached normal for both groups, indicating remodeling of the LV geometry after aortic valve replacement.

Evaluation of cardiac function during left ventricular assist by a centrifugal blood pump.

In this study, the effects on varying cardiac function during a left ventricular (LV) bypass from the apex to the descending aorta using a centrifugal blood pump were evaluated by analyzing the left ventricular pressure and the motor current of the centrifugal pump in a mock circulatory loop. Failing heart models (preload 15 mm Hg, afterload 40 mm Hg) and normal heart models (preload 5 mm Hg, afterload 100 mm Hg) were simulated by adjusting the contractility of the latex rubber left ventricle. In Study 1, the bypass flow rate, left ventricular pressure, aortic pressure, and motor current levels were measured in each model as the centrifugal pump rpm were increased from 1,000 to 1,500 to 2,000. In Study 2, the pump rpm were fixed at 1,300, 1,500, and 1,700, and at each rpm, the left ventricular peak pressure was increased from 40 to 140 mm Hg by steps of 20 mm Hg. The same measurements as in Study 1 were performed. In Study 1, the bypass flow rate and mean aortic pressure both increased with the increase in pump rpm while the mean left ventricular pressure decreased. In Study 2, a fairly good correlation between the left ventricular pressure and the motor current of the centrifugal pump was obtained. These results suggest that cardiac function as indicated by left ventricular pressure may be estimated from a motor current analysis of the centrifugal blood pump during left heart bypass.

Evaluation of an implantable motor-driven left ventricular assist device.

A console based implantable motor-driven left ventricular assist device (LVAD) was developed and tested. Ten sheep weighing 42-73 kg (mean, 54.4 kg) were used as the experimental animals. Four animals survived 5-12 h (mean, 9.5 h). The mean pump flow was 1.63 L/min, ranging from 0.8 to 2.5 L/min. The cause of termination was respiratory failure in 3 animals, bleeding in 2, ventricular fibrillation in 2, vent tube obstruction in 1, thrombus formation in 1, and mechanical failure of the driving console in 1. Following the in vivo studies, the computer regulated controller was tested in a mock circulatory system. The LVAD provided 5.34 L/min of maximum output against a mean afterload of 80 mm Hg with a filling pressure of 15 mm Hg when the pump rate was 80 bpm in the fixed rate mode. With an increase in the pump afterload from 80 to 140 mm Hg, the total system efficiency varied from 7.81 to 8.34% when the pump preload was 15 mm Hg. An ultracompact, completely implantable electromechanical VAD has been under development. This device should fit in a 60 kg adult. As the next step, we are preparing to implant this ultracompact implantable VAD with an electronic controller in an animal model with better results being expected.

Left ventricular mass regression after implantation of St. Jude Medical cardiac valves in small aortic roots.

In this study, we analyzed the extent of regression of left ventricular hypertrophy in patients who received small St. Jude Medical (SJM) aortic valves and compared the results with those of another group receiving larger valves. Eighty-eight patients received either 19 or 21 mm valves (Group 1, 25 patients) or either 23 or 25 mm valves (Group 2, 53 patients). Echocardiographic studies were done before the operation and 5 years postoperatively. At follow-up a significant reduction in the left ventricular mass was found for both patient groups (p < 0.0001). Doppler echocardiography derived pressure gradients for both groups were obtained during the follow-up period. As expected, the patients in Group 1 had higher peak pressure gradients than did those in Group 2. However, there was no significant difference between the 2 groups or any significant correlations between peak pressure gradients and body surface area (BSA). Actuarial survival was 84.7% at 15 years for Group 1 and 85.9% at 17 years for Group 2. Actuarial freedom from valve related events was 91.4% at 15 years for Group 1 and 82.7% at 17 years for Group 2. There was no significant difference in survival or valve related event free curves between the 2 groups. After implantations of SJM valves in small aortic roots, significant left ventricular mass regression was obtained, and the results were comparable to those for valves of other sizes. The long-term performance of aortic valve replacement with small valves was satisfactory as judged by improvement in the functional class of patients and survival statistics, the durability of the prosthesis, and valve related morbidity comparable to that of valves of other sizes.

[Long-term follow-up of patients with small St. Jude aortic valve prostheses].

Thirty-five patients received small sized 19 or 21 mm valves (group I) and 53 patients received 23 or 25 mm valves (group II). At follow-up a significant reduction in the left ventricular mass was found for both patient groups (p < 0.0001). The patients in group I had higher peak pressure gradients than did those in group II. However, there was no significant difference between the two groups, or any significant correlation between peak pressure gradients and body surface area. Actuarial survival was 84.7% at 15 years for group I and 85.9% at 17 years for group II. Actuarial freedom from valve-related events was 91.4% at 15 years for group I and 82.7% at 17 years for group II. There was no significant difference in survival or valve-related event free curves between the two groups. After implantation of small SIM valves, significant left ventricular mass regression was obtained and the results were comparable to those for valves of other sizes. The long-term performance of aortic valve replacement with small valves was satisfactory as judged by improvement in the functional class of patients, survival statistics, the durability of the prosthesis, and valve related morbidity comparable to that of valves of other sizes.

[Long-term results of emergency coronary artery bypass grafting].

During a 20-year period, 364 patients underwent coronary artery bypass grafting (CABG) for the treatment of ischemic heart disease. Among these patients, 28 underwent emergency surgery. The reasons for performing emergency CABG were unstable angina in 15 patients, impending myocardial infarction in 12 patients, and congestive heart failure in 1 patient. Eleven patients died postoperatively. Eight variables were examined by univariate analysis for their influence on the occurrence of a hospital death. IABP and acute coronary occlusion were found to be predictors of hospital death and previous myocardial infarction was a predictor of hospital survival. Seventeen patients were followed up for 12 years. There was no cardiac death and actuarial survival at 12 years was 63%. The 14 survivors are now in NYHA functional class I or II. Although the operative mortality rate is high after emergency CABG, the patient's prognosis is good.

Long-term results of emergency coronary artery bypass grafting.

During a 20-year period, 364 patients underwent coronary artery bypass grafting (CABG) for the treatment of ischemic heart disease. Among these patients, 28 underwent emergency surgery. The reasons for performing emergency CABG were unstable angina in 15 patients, impending myocardial infarction in 12 patients and congestive heart failure in 1 patient. Eleven patients died postoperatively. Eight variables were examined by univariate analysis for their influence on the occurrence of a hospital death. Lack of a history of myocardial infarction, intraaortic balloon pumping (IABP) and acute coronary occlusion were all found to be predictors of hospital death. Seventeen patients were followed up for 12 years. There was no cardiac death and actuarial survival at 12 years was 63%. The 14 survivors are now in NYHA functional class I or II. Although the operative mortality rate is high after emergency CABG, a fair prognosis can be expected if the patients survive surgery.

[A case of swallowed fish bone-induced esophageal perforation and mediastinitis treated with pedicled omental graft].

We experienced a case of 47-year-old man who suffered swallowed fish bone-induced esophageal perforation with purulent mediastinitis and underwent direct suture closure of the perforation and reinforcement with a pedicled parietal pleura four days after the onset. Postoperative esophageal suture insufficiency was occured and reoperation was performed two months after the first operation. The esophageal fistula was plugged with a pedicled omental graft successfully. The postoperative course of the patient was uneventful and he discharged 45 days after the second operation. A reinforcement by pedicled omental graft for esophageal rupture accompanied with mediastinitis was considered to be a useful procedure.

In vitro and in vivo testing of an implantable motor-driven left ventricular assist device.

A totally implantable motor-driven left ventricular assist device (LVAD) has been developed and tested. The performance of this LVAD was tested in a mock circulatory system. This pump provided 8 L/min of output against a mean afterload of 120 mm Hg with a filling pressure of 20 mm Hg when the pump was operated in the fill/empty mode. The right and left pumps were tested in a mock loop. The right pump afterload was kept in the range from 23-32 mm Hg. With increase in the left pump afterload, the pump power output varied from 1.64 to 2.37 W. The instantaneous motor power input varied from 22.6 to 30.6 W with the total system efficiency ranging from 6.7 to 9.4%. To date, 4 in vivo studies have been conducted for up to 12 h. Two animals survived 12 and 10 h, respectively. Termination was due to bleeding in 1 animal, vent tube obstruction in 1, and respiratory failure in 2. All animals died of technical failure. Another experiment is to be undertaken, and a newly designed cannula is now being manufactured.