Takehide Akimoto

HeartMate III: pump design for a centrifugal LVAD with a magnetically levitated rotor.

A long-term, compact left ventricular assist device (LVAD), the HeartMate III, has been designed and fabricated, featuring a centrifugal pump with a magnetically levitated rotor. The pump has been optimized by in vitro testing to achieve a design point of 7 L/min against 135 mm Hg at high hydrodynamic efficiency (30%) and to be capable of up to 10 L/min under such a load. Furthermore, the pump has demonstrated no mechanical failures, low hemolysis (4–10 mg/dl plasma free Hb), and low thrombogenicity during six (40, 27, 59, 42, 27, and 49-day) in vivo bovine studies.

A miniature intraventricular axial flow blood pump that is introduced through the left ventricular apex.

A new intraventricular axial flow blood pump has been designed and developed as an implantable left ventricular assist device (LVAD). The pump consists of a tube housing (10 cm in length and 14 mm in diameter), a three-vane impeller combined with a guide vane, and a DC motor. This pump is introduced into the LV cavity through the LV apex, and the outlet cannula is passed antegrade across the aortic valve. Blood is withdrawn from the LV through the inlet ports at the pump base, and discharged into the ascending aorta. A pump flow of > 8 L/min was obtained against 90 mmHg differential pressure in the mock circulatory system. In an acute dog model, this pump could produce a sufficient output of 200 ml/kg/min. In addition, the pump flow profile demonstrated a pulsatile pattern, although the rotation speed was fixed. This is mainly due to the changes in flow rate during a cardiac cycle--that is, during systole, the flow rate increases to the maximum, while the differential pressure between the LV and the aorta decreases to the minimum. Thus, this simple and compact axial flow blood pump can be a potential LVAD, with prompt accessibility and need for less invasive surgical procedures.

Operation for type A aortic dissection: introduction of retrograde cerebral perfusion

Circulatory support during operation for type A aortic dissection is controversial among many medical centers. In the last 21 years, 100 patients with type A aortic dissection underwent 102 operations including 2 reoperations, and 29 patients showed Marfans syndrome. During operation, no cerebral perfusion technique was used through February 1985 (period I), antegrade cerebral perfusion was applied since March 1985 (period II), and retrograde cerebral perfusion was introduced in November 1990 (period III). Surgical results were compared among these subgroups. Operative mortality was 12.1% in 33 chronic and 57.1% in 7 acute patients in period I, 11.1% in 27 chronic and 54.5% in 11 acute patients in period II, and 6.7% in 15 chronic and 0% in 9 acute patients in period III (period II versus III; p = 0.04). Retrograde cerebral perfusion decreased permanent brain complications. The 5-year actuarial survival was 59.7% in period I and 63.2% in period II (not significant), and the 3-year survival of period III was 91.7%. Actuarial survival of period III was significantly higher than those of periods I and II (p < 0.05). Surgical repair of aortic arch with cerebral perfusion techniques reduced the residual aneurysms. These results show that surgical results of type A aortic dissection in this series improved with the introduction of retrograde cerebral perfusion and extended surgical procedures.

Relationship of blood pressure and pump flow in an implantable centrifugal blood pump during hypertension.

The purpose of this study was to evaluate the real time relationship between pump flow and pump differential pressure (D-P) during experimentally induced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EVAHEART centrifugal blood pump (SunMedical Technology Research Corp., Nagano, Japan) under general anesthesia. Blood pressure (BP) in diastole was increased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, ECG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All data were separated into systole and diastole, and pump flow during HT was compared with normotensive (NT) conditions at respective pump speeds. Diastolic BP was increased to 99.3 ± 4.1 mm Hg from 66.5 ± 4.4mm Hg (p < 0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) even during HT. During NT, the average systolic pump flow volume was 60% of the total pump flow. However, during HT, the average systolic pump flow was 100% of total pump flow volume, although the pump flow volume in systole during HT decreased (33.1 ± 5.7 vs 25.9 ± 4.0 ml/systole, p < 0.01). In diastole, the average flow volume through the pump was 19.6 ± 6.9 ml/diastole during NT and −2.2 ± 11.1 ml/diastole during HT (p < 0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p < 0.001). This study suggests that the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow.

Operation for type B aortic dissection: Introduction of left heart bypass

Various support techniques for surgical treatment of type B aortic dissection have been used and recommended in many medical centers. In the last 21 years, 55 patients with type B aortic dissection underwent 65 operations including 10 reoperations, and 10 cases showed Marfans syndrome. As circulatory support during operation, venoarterial bypass mainly was used until March 1987 (period I) and low-dose heparinized left heart bypass was applied since April 1987 (period II). Surgical results were compared among subgroups by the Kaplan-Meier actuarial method and Cox-Mantel statistical analysis. After the operation, early mortality was 27.3% in 33 patients in period I and 9.4% in 32 patients in period II (p = 0.06). The incidence of fatal hemorrhagic complications was decreased significantly by using the left heart bypass technique (p < 0.02). The 5-year actuarial survival of type B dissection was 60.6% in period I and 79.2% in period II (p = 0.07). These results suggest that surgical results of type B aortic dissection in this series might be improved with the introduction of left heart bypass and extended surgical procedures.

Influence of previous percutaneous coronary intervention on clinical outcome of coronary artery bypass grafting: a meta-analysis of comparative studies

The prognostic significance of previous percutaneous coronary intervention (PCI) in patients undergoing coronary artery bypass grafting (CABG) is still unclear. Although many studies have reported adverse effects of previous PCI on postoperative mortality in CABG, as yet no meta-analysis has been carried out. We conducted this first meta-analysis to assess whether previous PCI increases postoperative mortality in CABG. MEDLINE and EMBASE were searched for relevant articles up to and including April 2014. Studies published in English satisfying the following criteria were included in the meta-analysis: (i) comparing CABG patients with previous PCI versus without previous PCI; and (ii) reporting hospital mortality. Our search identified 23 comparative studies, including 174 777 patients: 19 179 with previous PCI and 155 598 without previous PCI. Pooled analysis demonstrated that previous PCI had an adverse effect on hospital mortality: odds ratio (OR) 1.187, 95% confidence interval (CI) 1.075-1.312. Furthermore, subgroup analysis stratified by the proportion of multiple previous PCI (i.e. number of patients with multiple previous PCI/number of patients with single or multiple previous PCI) was performed. In the subgroup of studies with the proportion <40%, the adverse effect was not significant: OR 0.897 (95% CI 0.723-1.113); however, in the subgroup of studies with the proportion ≥ 40%, the adverse effect of previous PCI was significant: OR 1.987 (95% CI 1.563-2.526). A meta-regression coefficient was significantly positive for the proportion of patients with a history of multiple PCI (coefficient 0.841; 95% CI 0.457-1.226; P < 0.001). This meta-analysis would argue that as the proportion of patients with multiple previous PCI in the CABG cohort increases, postoperative mortality also increases. This result re-emphasizes the importance of the heart team approach to coronary revascularization.

Postcardiotomy patients treated with mechanical circulatory support: Potential candidates for a bridge to transplantation

Twenty-six patients with postcardiotomy heart failure required mechanical circulatory support in addition to balloon pumping, among 1686 adult cardiac operations at the Heart Institute of Japan. Four types of assisted circulation were undertaken, and the duration ranged from 3 to 312 (mean 50) hours. Ten patients (39%) could not be weaned from circulatory support. Seven cases were lost due to device-related complications or fatal arrhythmias after weaning. The remaining 9 patients (35%) were discharged from the hospital. According to causes of death, an advanced ventricular assist system or bridge bypass was necessary for 10 patients with biventricular failure or ventricular fibrillation. It was concluded that four patients with irreversible cardiac damage and no other organ dysfunction might have been potential candidates for circulatory support as a bridge to transplantation.

Off-pump technique reduces surgical mortality after elective coronary artery bypass grafting in patients with preoperative renal failure

Objectives Most randomized controlled trials of off‐pump versus on‐pump coronary artery bypass grafting (CABG) have included limited numbers of patients with preoperative renal failure. This study was performed to evaluate the association between the clinical benefit of the off‐pump technique and chronic kidney disease stage. Methods We analyzed 38,051 patients with chronic kidney disease who underwent primary nonemergent isolated CABG from 2013 to 2015 as reported in the Japan Cardiovascular Surgery Database‐Adult section. These patients were stratified into 4 categories according to their estimated glomerular filtration rate (eGFR) of 60 to 90, 30 to 59, and <30 mL/min/1.73 m2, and hemodialysis‐dependent. The clinical outcomes were compared between patients undergoing off‐pump and on‐pump CABG in each stratum using inverse probability of treatment weighting. Results In total, 23,634 (62.1%) patients were intended for off‐pump CABG. In patients with mildly reduced renal function (eGFR 60–89 mL/min/1.73 m2), there was no significant risk reduction effect of off‐pump CABG for surgical mortality. Conversely, in patients with moderate or severe renal disease (eGFR <60 mL/min/1.73 m2), off‐pump CABG was associated with a significantly lower incidence of surgical death (odds ratio with 95% confidence interval: eGFR 30–59 mL/min/1.73 m2, 0.66 [0.51–0.84]; eGFR <30 mL/min/1.73 m2, 0.51 [0.37–0.72]; and hemodialysis‐dependent, 0.68 [0.51–0.90]). In addition, in patients with severe renal disease (eGFR of <30), off‐pump CABG was associated with a significantly lower incidence of de novo dialysis. Conclusions The off‐pump technique significantly reduced surgical mortality in patients with moderate or severe preoperative renal dysfunction.

The Relationship between Tension and Length of the Aortic Adventitia Resected from the Aortic Wall of Acute Aortic Dissection.

OBJECTIVE To our knowledge, no previous study has described the measurement of the tensile strength of the human aortic adventitia. In the present study, we examined the relationship between the tension and length of the aortic adventitia resected from the aortic wall of patients with acute aortic dissection. METHODS We obtained rectangular specimens from the aortic adventitia that was resected in patients with acute aortic dissection during surgery. The specimens were placed on a tension meter (Digital Force Gauge FGS-10, SHIMPO, Kyoto, Japan) within 15 min after resection and stretched until they were pulled apart, and the tension and length were recorded. RESULTS We obtained 18 specimens during surgery from 11 cases of acute aortic dissection. When the specimen was being pulled apart, the mean tension recorded was 10.2 ± 4.9 N/cm specimen width, whereas the mean elongated length recorded was 4.2 ± 1.1 mm/cm specimen length. DISCUSSION We determined that the aortic adventitia is elastic and expandable up to 140% of its original length. This indicates that dilation of the aorta to >4.2 cm in diameter may result in a rupture if the original aortic diameter prior to dissection was 3 cm. (English translation of J Jpn Coll Angiol 2013; 53: 77-81).

Distal thoracic aorta hemodynamics during exercise with continuous flow left ventricular assist system

Objectives: Continuous flow left ventricular assist systems (LVAS) are being discussed as a destination therapy. LVAS patients will have expanded activity of daily life, including exercise. In this study, we analyzed the effects of exercise on blood flow in the distal thoracic aorta of LVAD implanted animals. Methods: Five calves with a continuous flow LVAS exercised on treadmill at two different pump flow rates (PFR), 60 ‐ 80% (high PFR) and 25 ‐ 30% (low PFR) of pulmonary artery flow rate. Pump, pulmonary artery and descending thoracic aorta flow waves were recorded before, during and after exercise. Systolic and diastolic flow volume in each cardiac cycle in pump and descending thoracic aorta flow was calculated. Results: (1) Average flow rates ‐ Pulmonary artery and descending thoracic aorta flow rates increased with heart rate during exercise and there was no difference between groups. (2) Pump flow wave ‐ Pump regurgitation increased temporally during exercise at both PFRs, but sustained incidences of regurgitation after exercise were only observed at low PFR. Systolic and diastolic pump flow volume decreased during exercise at both PFRs, but systolic volume increased and diastolic volume decreased significantly after exercise at low PFR. (3) Descending thoracic aorta flow wave ‐ At high PFR, systolic volume of descending thoracic aorta increased but diastolic flow volume decreased during exercise. At low PFR, both systolic and diastolic volume of the descending thoracic aorta decreased during exercise, but systolic volume increased and diastolic volume decreased after exercise. Systolic volume of the descending thoracic aorta in low PFR was significantly greater and diastolic volume was less than those in high PFR during and after exercise. Conclusion: Exercise temporarily increases pump regurgitation with continuous flow LVAS support. Average flow rate of the descending thoracic aorta was maintained by compensation from increased heart rate, although the diastolic flow of the descending thoracic aorta decreased after exercise at the lower pump flow rate. Further study will be needed to evaluate whether or not this flow decrease causes hemodynamic and/or an oxygen delivery mismatch to peripheral tissue. q 2003 Elsevier B.V. All rights reserved.