A case of hypervirulent K1-ST23 Klebsiella pneumoniae endocarditis and papillary muscle rupture secondary to multiple site abscesses.

Hypervirulent Klebsiella pneumoniae (hvKP) causes multisite infections and abscesses. However, endocarditis is a rare presentation of hvKP infection. Herein, we report a case of K. pneumoniae native valve infective endocarditis secondary to community-acquired liver and prostate abscesses. The patient developed papillary muscle rupture, leading to mitral regurgitation, and underwent emergent mitral valve replacement. The diagnosis of endocarditis was confirmed microbiologically and histologically. The causative strain belonged to the hypermucoid K1 capsular genotype and possessed the rmpA gene. The genome sequence was deposited in GenBank under the accession number JAQZBZ000000000.

[Aortic Root Replacement with Homograft].

Infectious endocarditis is a severe infectious disease in cardiovascular surgery fields. Appropriate antibiotics administration is the principle of treatment, while surgical intervention is required when there is intensive tissue destruction, refractory infection, or high risk of embolism. Usually, surgical risks of infectious endocarditis are rather high as preoperative general condition is often poor. Homografts, which have excellent anti-infective properties, become one of the graft options for infectious endocarditis. Fortunately, we are able to use homografs without so much obstacles thanks to the presence of a tissue bank in our hospital. We will report our strategy and clinical courses of aortic root replacement using homograft for infective endocarditis.

Perigraft seroma after total aortic arch replacement using Triplex graft.

A 42-year-old gentleman underwent total aortic arch replacement with Triplex graft (Terumo corporation, Tokyo, Japan) for acute type A dissection. Sixteen months later, a computed tomography revealed a rapidly enlarging low-density area around the graft, with no contrast enhancement. The area was compressing the mediastinal structures, such as the superior vena cava and right pulmonary artery. Suspecting lymphorrhea or perigraft seroma (PGS), surgical drainage was performed. Although fluid accumulation around the graft was cloudy and yellowish, Gram stain was negative. A fatty preparation was administered from the nasogastric tube, demonstrating no leakage of chyle. Intraoperative lymphangiography with indocyanine green also showed no lymphatic leak. Therefore, PGS was suspected. Fibrin glue was applied to the graft and the surgery was completed. PGS drainage after arch replacement, especially with Triplex graft, is extremely rare. We discuss the strategies of diagnosis and treatment for this uncommon complication after aortic surgery.

Association between left ventricular ejection fraction and mortality after Bentall procedure.

Root infection or dissection involving coronary artery frequently necessitates an emergent Bentall procedure, with low left ventricular ejection fraction (LVEF). In contrast, concerning an elective Bentall for aneurysm, surgeons should balance the risk and benefit of surgery, especially in low LVEF cases. We investigated the association between preoperative LVEF and outcomes after Bentall. We analyzed 98 patients undergoing Bentall between April 2000 and March 2020. The patients were stratified into three groups: (a) 65 with LVEF ≥ 60%, (b) 21 with LVEF 45 to < 60%, and (c) 12 with LVEF < 45%. Baseline characteristics, survivals, and major adverse cardiovascular events (MACE) were compared. To assess potential non-linear relationship between LVEF and mortality, cubic spline analysis was conducted. Median age was similar (a vs b vs c, 52 vs 50 vs 44). In all groups, elective root aneurysm was 50-60%, indicating the rest were complicated and sick. Operative mortality was the highest in group c (4.6% vs 9.5% vs 16.7%, p = 0.294). Survival and MACE-free rate were the worst in group c, though their 10-year survival was 40%. LVEF was an independent risk for mortality, and cubic spline analysis showed potential non-linear association between LVEF and mortality. Although LVEF is an independent predictor of mortality after Bentall, long-term survival was occasionally achieved in low LVEF cases. While surgeons should carefully balance the risk of low LVEF and the benefit of surgery in elective cases, we should perform a non-elective procedure as needed, even if LVEF is low.

Continuous measurement of surface electrical potentials from transplanted cardiomyocyte tissue derived from human-induced pluripotent stem cells under physiological conditions in vivo.

Recording the electrical potentials of bioengineered cardiac tissue after transplantation would help to monitor the maturation of the tissue and detect adverse events such as arrhythmia. However, a few studies have reported the measurement of myocardial tissue potentials in vivo under physiological conditions. In this study, human-induced pluripotent stem cell-derived cardiomyocyte (hiPSCM) sheets were stacked and ectopically transplanted into the subcutaneous tissue of rats for culture in vivo. Three months after transplantation, a flexible nanomesh sensor was implanted onto the hiPSCM tissue to record its surface electrical potentials under physiological conditions, i.e., without the need for anesthetic agents that might adversely affect cardiomyocyte function. The nanomesh sensor was able to record electrical potentials in non-sedated, ambulating animals for up to 48 h. When compared with recordings made with conventional needle electrodes in anesthetized animals, the waveforms obtained with the nanomesh sensor showed less dispersion of waveform interval and waveform duration. However, waveform amplitude tended to show greater dispersion for the nanomesh sensor than for the needle electrodes, possibly due to motion artifacts produced by movements of the animal or local tissue changes in response to surgical implantation of the sensor. The implantable nanomesh sensor utilized in this study potentially could be used for long-term monitoring of bioengineered myocardial tissue in vivo under physiological conditions.

Long-term support by left ventricular assist device for arrhythmogenic right ventricular cardiomyopathy.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a heart muscle disorder characterized by right ventricular enlargement, right heart failure (HF), and ventricular arrhythmias which lead to sudden death especially in young adults. Current recommendations for management of patients with ARVC are antiarrhythmic medications, catheter ablation, and implantable cardioverter defibrillator therapy to prevent sudden cardiac death. However, despite these treatments, few patients suffer from recurrent ventricular arrhythmias or HF unresponsive to conventional management. Heart transplantation (HTx) is a preferred treatment for these cases, but because of a persistent donor heart shortage in Japan, ventricular assist device (VAD) support has become an important option for a management of the end-stage ARVC. Previous articles reported 4 cases of a successful management by left ventricular assist device (LVAD), but the longest interval of LVAD support was only 333 days. We present 3 cases of ARVC patients who were successfully managed by LVAD implantation for more than a year. These 3 cases are unconventional examples of ARVC patients, considering the nature of the disease. The novelty of these cases should be taken in the context of the extremely long waiting period for HTx in Japan.

Cell Sheet-Based Vascularized Myocardial Tissue Fabrication.

BACKGROUND: The development of regenerative medicine in recent years has been remarkable as tissue engineering technology and stem cell research have advanced. The ultimate goal of regenerative medicine is to fabricate human organs artificially. If fabricated organs can be transplanted medically, it will be the innovative treatment of diseases for which only donor organ transplantation is the definitive therapeutic method at present. SUMMARY: Our group has reported successful fabrication of thick functional myocardial tissue in vivo and in vitro by using cell sheet engineering technology which requires no scaffolds. Thick myocardial tissue can be fabricated by stacking cardiomyocyte sheets on the vascular bed every 24 h, so that a vascular network can be formed within the myocardial graft. We call this procedure a multi-step transplantation procedure. After human-induced pluripotent stem cells were discovered and human cardiomyocytes became available, a thick, macroscopically pulsate human myocardial tissue was successfully constructed by using a multi-step transplantation procedure. Furthermore, our group succeeded in fabricating functional human myocardial tissue which can generate pressure. Here, we present our way of fabricating human myocardial tissue by means of cell sheet engineering technology. Key Messages: Our group succeeded in fabricating thick, functional human myocardium which can generate pulse pressure. However, there are still a few problems to be solved until clinically functional human cardiac tissue or a whole heart can be fabricated. Research on myocardial regeneration progresses at such a pace that we believe the products of this research will save many lives in the near future.

Three-dimensional functional human myocardial tissues fabricated from induced pluripotent stem cells.

The most radical treatment currently available for severe heart failure is heart transplantation; however, the number of donor hearts is limited. A better approach is to make human cardiac tissues. We developed an original cell sheet-based tissue-engineering technology to fabricate human cardiac tissue by layering myocardial cell sheets. Human induced pluripotent stem (iPS) cells were differentiated into cardiomyocytes to fabricate cardiomyocyte sheets. Initially, three-layer human iPS cardiomyocyte (hiPSCM) sheets were transplanted on subcutaneous tissues of nude rats. Next, to fabricate thicker tissue, three-layer sheets were transplanted on one day, then additional three-layer sheets were transplanted onto them the following day, after the first sheets were vascularized. On day 3, the final three-layer sheets were again transplanted, creating a nine-layer graft (multi-step transplantation procedure). In the last step, six-layer sheets were transplanted on fat tissues of the inguinal portion, which were subsequently resected together with the femoral arteries and veins to make transplantable grafts with connectable vessels. They were then transplanted ectopically to the neck portion of other rats by anastomosing vessels with the host's jugular arteries and veins. Transplanted three-layer hiPSCMs were beating and, histologically, showed a cardiac muscle-like structure with vascular systems. Moreover, transplanted hiPSCMs proliferated and matured in vivo. Significantly thicker tissues were fabricated by a multi-step transplantation procedure. The ectopically transplanted graft survived and continued to beat. We succeeded in fabricating functional human cardiac tissue with cell sheet technology. Transplanting this cardiac tissue may become a new treatment option for severe heart failure. Copyright © 2015 John Wiley & Sons, Ltd.

Left ventricular pseudoaneurysm after surgery for infective endocarditis.

A 46-year-old man had undergone aortic valve replacement for aortic regurgitation due to active infective endocarditis in 2006. He had been followed by transthoracic echocardiography revealing results within normal limits except for a subannular depressed scar. In 2010, a giant left ventricular pseudoaneurysm was detected on three-dimensional computed tomography. We performed surgery for patch closure of the pseudoaneurysm and redo aortic valve replacement.

Aortic pseudoaneurysm due to graft infection after invasive thymoma resection.

A 69-year-old woman with invasive thymoma underwent chemoradiotherapy followed by surgical resection, including extended thymectomy, right upper lobectomy, and innominate vein and superior vena cava reconstruction with a polytetrafluoroethylene graft. Computed tomography on the 27th postoperative day revealed mediastinitis and right hemothorax; open debridement and evacuation were performed. Vacuum-assisted closure was initiated to heal the median incision. The wound gradually cleared, and the vacuum was terminated on the 150th postoperative day. On the 155th postoperative day, the patient suffered a sudden hemorrhage from the anterior thoracic wall. Computed tomography revealed a ruptured ascending aortic pseudoaneurysm surrounding the graft.