Katsuji Fujiwara

Burst Emergence of Intracellular Ca2+ Waves Evokes Arrhythmogenic Oscillatory Depolarization via the Na+–Ca2+ Exchanger Simultaneous Confocal Recording of Membrane Potential and Intracellular Ca2+ in the Heart

Intracellular Ca2+ waves (CaWs) of cardiomyocytes are spontaneous events of Ca2+ release from the sarcoplasmic reticulum that are regarded as an important substrate for triggered arrhythmias and delayed afterdepolarizations. However, little is known regarding whether or how CaWs within the heart actually produce arrhythmogenic membrane oscillation because of the lack of data confirming direct correlation between CaWs and membrane potentials (Vm) in the heart. On the hypothesis that CaWs evoke arrhythmogenic oscillatory depolarization when they emerge synchronously and intensively in the heart, we conducted simultaneous fluorescence recording of intracellular Ca2+ ([Ca2+]i) dynamics and Vm of ventricular myocytes on subepicardial surfaces of Langendorff-perfused rat hearts using in situ dual-view, rapid-scanning confocal microscopy. In intact hearts loaded with fluo4/acetoxymethyl ester and RH237 under perfusion with cytochalasin D at room temperature, individual myocytes exhibited Ca2+ transients and action potentials uniformly on ventricular excitation, whereas low-K+–perfused (2.4 mmol/L) hearts exhibited CaWs sporadically between Ca2+ transients without discernible membrane depolarization. Further [Ca2+]i loading of the heart, produced by rapid pacing and addition of isoproterenol, evoked triggered activity and subsequent oscillatory Vm, which are caused by burst emergence of CaWs in individual myocytes. Such arrhythmogenic membrane oscillation was abolished by ryanodine or the Na+–Ca2+ exchanger inhibitor SEA0400, indicating an essential role of CaWs and resultant Na+–Ca2+ exchanger–mediated depolarization in triggered activity. In summary, we demonstrate a mechanistic link between intracellular CaWs and arrhythmogenic oscillatory depolarizations in the heart. Our findings provide a cellular perspective on abnormal [Ca2+]i handling in the genesis of triggered arrhythmias in the heart.

Generation of reentrant arrhythmias by dominant-negative inhibition of connexin43 in rat cultured myocyte monolayers

AIMS Alteration of connexin43 (Cx43)-mediated intercellular communication is known to promote susceptibility to ventricular tachyarrhythmias. However, the precise mechanism of the altered Cx43 responsible for arrhythmogenesis remains unclear. We sought to understand changes in impulse propagation of ventricular myocytes under dominant-negative (DN) inhibition of Cx43 in the development of arrhythmias. METHODS AND RESULTS Intercellular communication was inhibited in confluent monolayers of neonatal rat cultured myocytes by an adenoviral vector-mediated gene transfer for DNCx43-fused red fluorescence protein (RFP). A high-resolution, macro-zoom fluorescence imaging system was used to visualize both the fluo4- and RFP-fluorescence intensities as measures of Ca2+ transient propagation and distribution of DNCx43 inhibition, respectively, in the myocyte monolayers. DNCx43 inhibition of the monolayers resulted in not only a significant slowing of Ca2+ transient propagation velocity, but also a preferential emergence of spiral-wave reentrant arrhythmias elicited by rapid pacing. Detailed observations on the development of spiral waves revealed that the gene-transferred myocyte monolayers exhibited regional slowing of propagation and subsequent generation of wave break, resulting in reentrant arrhythmias. Furthermore, DNCx43-RFP-transferred monolayers showed higher fluorescence intensity of RFP at the break point than at the surrounding myocardium, indicating a culprit role of DNCx43 inhibition in the genesis of spiral reentry. CONCLUSION The present results indicate that regional heterogeneity in gap-junctional communication promotes, in addition to slowing of conduction velocity, susceptibility to reentrant tachyarrhythmias.

Improvement of depth resolution on photoacoustic imaging using multiphoton absorption

Commercial imaging systems, such as computed tomography and magnetic resonance imaging, are frequently used powerful tools for observing structures deep within the human body. However, they cannot precisely visualized several-tens micrometer-sized structures for lack of spatial resolution. In this presentation, we propose photoacoustic imaging using multiphoton absorption technique to generate ultrasonic waves as a means of improving depth resolution. Since the multiphoton absorption occurs at only the focus point and the employed infrared pulses deeply penetrate living tissues, it enables us to extract characteristic features of structures embedded in the living tissue. When nanosecond pulses from a 1064-nm Nd:YAG laser were focused on Rhodamine B/chloroform solution (absorption peak: 540 nm), the peak intensity of the generated photoacoustic signal was proportional to the square of the input pulse energy. This result shows that the photoacoustic signals can be induced by the two-photon absorption of infrared nanosecond pulse laser and also can be detected by a commercial low-frequency MHz transducer. Furthermore, in order to evaluate the depth resolution of multiphoton-photoacoustic imaging, we investigated the dependence of photoacoustic signal on depth position using a 1-mm-thick phantom in a water bath. We found that the depth resolution of two-photon photoacoustic imaging (1064 nm) is greater than that of one-photon photoacoustic imaging (532 nm). We conclude that evolving multiphoton-photoacoustic imaging technology renders feasible the investigation of biomedical phenomena at the deep layer in living tissue.

Incomplete Atrioventricular Septal Defect With Hypoplastic Left Ventricle and Left Atrioventricular Valve Stenosis

A 2-month-old male infant with incomplete atrioventricular septal defect associated with a hypoplastic left ventricle and left atrioventricular valve stenosis successfully underwent biventricular repair. Echocardiography showed marked dilatation in the right ventricle and a diminutive left ventricle. However, the left ventricular chamber occupied the apex. Left atrioventricular valve stenosis was due to a solitary papillary muscle. Cardiac catheterization showed pulmonary/systemic flow ratio of 3.61, left ventricular end-diastolic volume of 63% of normal, and right ventricular end-diastolic volume of 324% of normal. During surgical repair, the solitary papillary muscle was divided longitudinally and the ostium primum was closed with a bovine pericardium. Postoperative left ventricular function was appropriate. Even when the preoperative end-diastolic left ventricular volume is small, if the left ventricle chamber is at the apex, then the left ventricular performance can be expected to be appropriate to tolerate the volume load after ostium primum closure.

Repair of partial anomalous pulmonary venous connection with a minimal atriotomy

We present an alternative surgical technique for the repair of a partial anomalous pulmonary venous connection to the higher segment of the superior vena cava. Although the atriotomy is limited in this technique, a sufficiently large systemic venous chamber overlapping to the outside of the superior vena cava can be created.

Complete augmentation of diffuse narrowing of the aorta with Williams syndrome by using an overturn approach

One-staged complete augmentation of diffuse narrowing of the aorta extending from the ascending aorta (AAo) to the descending aorta (DAo) with Williams syndrome is extremely difficult because of the lack of a good surgical approach. For the treatment of diffuse aortic stenosis, we report an innovative surgical technique involving unifocalization of the neck branch arteries and complete aortic augmentation by using an overturn approach.

Oblique plication for repair of the atrialized ventricle and tricuspid incompetence of Ebstein’s anomaly

An 8-year-old girl who weighed 42 kg presented Ebsteins anomaly with severe tricuspid incompetence, and mild systemic cyanosis during exercise. A new reconstructive procedure for this complex anomaly was used. Oblique transference of the displaced posterior leaflet was performed, which resulted in plication of the atrialized ventricle and reduction in the tricuspid annular diameter. This procedure requires neither detachment nor closure of the tricuspid valve.

New “right side median” approach for postoperative re-coarctation of the aorta

Anatomic repair of postoperative recurrent coarctation of the aorta is surgically difficult using the conventional lateral approach. Therefore, we have developed a new approach to the stenotic aorta through a median sternotomy, involving division of the superior vena cava and left caudal displacement of the heart. This approach facilitates extensive dissection and mobilization of the descending aorta in the posterior mediastinum behind the heart and also facilitates direct anastomosis of the aortic arch and the descending aorta after resection of the stenosis. This approach is useful for anatomic repair of postoperative recurrent coarctation of the aorta and other posterior mediastinal procedures.

A Successful Case of Sutureless Pulmonary Artery Plasty Using Autologous Tissue for Severe Pulmonary Stenosis after a Rastelli Operation.

症例は7年前に当院でラステリ手術(Carpentier-Edwards 14mm弁付きグラフト)および左肺動脈形成術を受けた心室中隔欠損および肺動脈閉鎖の11歳男児.術後7年目の心臓カテーテル検査にてグラフトの狭窄と左肺動脈高度狭窄を認めた.左肺動脈は最狭部2mmしかなかったが,周囲を十分に剥離し,内膜を切開することにより10mmの肺動脈口径を確保し,周囲の癒着組織に縫合線をおき,ePTFE弁付きウシ心膜パッチを縫着した.術後経過は良好.術後3-D CTにて9mmの左肺動脈の開存を確認した.高度に狭窄した肺動脈であっても十分な剥離ののち周囲癒着組織を利用した形成術が有効であった.