Electrical superior vena cava isolation using photodynamic therapy in a canine model.

AIMS: With the new era of multi-tip radiofrequency or balloon ablation catheters replacing the point-to-point ablation strategy, we aimed to determine the feasibility of a ring-laser catheter ablation technology to electrically isolate the superior vena cava (SVC) by exploring the advantages of the limitless catheter tip size possibly with the photodynamic therapy (PDT)-mediated ablation. METHODS AND RESULTS: We developed a first-generation prototype of a circular-laser-mapping catheter by fitting a 7 cm plastic optical fibre onto a circular variable-loop Lasso™ mapping catheter. Following SVC venography, both the laser catheter and another ring catheter for monitoring the SVC potentials were placed at the SVC. After the systemic infusion of a photosensitizer (talaporfin sodium), we initiated the irradiation with an output of 1 W in three canines and 0.3 W in four. The creation of electrical isolation as well as occurrence of phrenic nerve injury, sinus node injury, and SVC stenosis were evaluated before, immediately after, and 1 month after the procedure. A PDT-mediated SVC isolation was successfully performed in all seven canines. The isolation was completed with a laser irradiation of 70.4 ± 71.4 J/cm under 30.9 ± 5.0 µg/mL of a photosensitizer without any sinus node injury, phrenic nerve palsy, or SVC stenosis in both the acute and chronic evaluations. The minimum isolation time of 270 s was not correlated with the laser input power or the photosensitizer concentration. CONCLUSION: The electrical SVC isolation was successfully and instantly achieved using the PDT laser-ring catheter without any complications.

Optimal conditions for cardiac catheter ablation using photodynamic therapy.

AIMS: Photodynamic therapy (PDT) is based on non-thermal injury mediated by singlet oxygen species and is used clinically in cancer therapy. In our continuing efforts to apply this technology to cardiac catheter ablation, we clarified the optimal condition for creating PDT-mediated lesions using a laser catheter. METHODS AND RESULTS: In a total of 35 canines, we applied a laser directly to the epicardium of the beating heart during open-chest surgery at 15 min after administration of a photosensitizer, talaporfin sodium. We evaluated the lesion size (depth and width) using hematoxylin-eosin staining under varying conditions as follows: laser output (5, 10, 20 W/cm(2)), irradiation time (0-60 s), photosensitizer concentration (0, 2.5, 5 mg/kg), blood oxygen concentration (103.5 ± 2.1 vs. 548.0 ± 18.4 torr), and contact force applied during irradiations (low: <20 g, high: >20 g). A laser irradiation at 20 W/cm(2) for 60 s under 5 mg/kg (29 µg/mL) of photosensitizer induced a lesion 8.7 ± 0.8 mm deep and 5.2 ± 0.2 mm wide. The lesion size was thus positively correlated to the laser power, irradiation time, and photosensitizer concentration, and was independent of the applied contact force and oxygen concentration. In addition, the concentration of the photosensitizer strongly correlated with the changes in the pulse oximetry data and fluorescence of the backscattering laser, suggesting that a clinically appropriate condition could be estimated in real time. CONCLUSION: Photodynamic therapy-mediated cardiac lesions might be controllable by regulating the photosensitizer concentration, laser output, and irradiation time.

Pericardial endoscopy-guided left atrial appendage ligation: a pilot study in a canine model.

BACKGROUND: Approaches for closing the left atrial appendage (LAA) have been developed for stroke prevention. However, the prevailing maneuvers require an open-chest surgery, intravascular access, or transseptal puncture. We evaluated the feasibility and safety of pericardial endoscopy-guided LAA ligation in a canine model. METHODS AND RESULTS: We used a total of 8 canines and computed tomography was performed before the procedures. After a double percutaneous pericardiocentesis, a transurethral rigid endoscope was inserted into the pericardial space. The ENDOLOOP ligature was advanced to the ostium of the LAA by counter pulling the tip of the LAA with forceps. After confirming the positioning guided by transesophageal echocardiography, the ligature was securely tightened. Acute success was evaluated by transesophageal echocardiography and chronic success was evaluated by blood testing, computed tomography, and transesophageal echocardiography. The LAA ligation was safely achieved in all canines without major complications. One month after the ligation, the ligated LAA was replaced by fibrotic tissue, and both the transesophageal echocardiography and computed tomographic images revealed no residual shunt. There was only a localized adhesion of the pericardium, where the original LAA was located, without the need for antibiotic or steroid administration. The postprocedural internal surface of the ligated LAA was smooth by virtue of intimal growth. Blood tests showed a slight elevation of the inflammatory markers, but this normalized spontaneously. CONCLUSIONS: Pericardial endoscopy-guided LAA ligation could provide an alternative, minimally invasive, and feasible solution for LAA closure that does not require vascular access or a transseptal puncture.

Effects of the selective KACh channel blocker NTC-801 on atrial fibrillation in a canine model of atrial tachypacing: comparison with class Ic and III drugs.

The present study examines the effects of NTC-801, a highly selective acetylcholine (ACh) receptor-activated potassium (KACh) channel blocker, on atrial fibrillation (AF) in a canine model with electrical remodeling. An experimental substrate for AF was created in dogs via left atrial (LA) tachypacing (400 bpm, 3-5 weeks). NTC-801, dofetilide, and flecainide were intravenously infused for 15 minutes, and the effects on AF inducibility, atrial effective refractory period (ERP), and atrial conduction velocity were examined. The effect of NTC-801 on AF termination was also evaluated. Atrial ERP was shortened and AF inducibility was increased after LA tachypacing. NTC-801 (0.3-3 µg·kg⁻¹·min⁻¹) prolonged atrial ERP irrespective of stimulation frequency and dose-dependently decreased AF inducibility. Dofetilide (5.3 µg·kg⁻¹·min⁻¹) and flecainide (0.13 mg·kg⁻¹·min⁻¹) did not significantly inhibit AF inducibility and minimally affected atrial ERP. Flecainide decreased atrial conduction velocity, whereas NTC-801 and dofetilide did not. NTC-801 (0.1 mg/kg) converted AF to normal sinus rhythm. In summary, NTC-801 exerted more effective antiarrhythmic effects than dofetilide and flecainide in a canine LA-tachypacing AF model. The antiarrhythmic activity of NTC-801 was probably due to prolonging atrial ERP independently of stimulation frequency. These results suggest that NTC-801 could prevent AF more effectively in the setting of atrial electrical remodeling.

Idiopathic ventricular tachycardia cured by radiofrequency application from the distal great cardiac vein and the left coronary cusp.

A 79 year-old male without structural heart disease suffered from drug refractory ventricular tachycardia (VT). VTs and premature ventricular complexes (PVCs) with the same morphology occurred incessantly with a concordant R pattern in chest leads and a tall R in Lead II, III, and aVF. The origin was expected to be near the left epicardial ventricular outflow tract (LVOT), which was termed the left ventricular summit area. Pace-mapping from the LVOT and the left coronary cusp (LCC) did not match well with the QRS morphology of the PVC. A good match was obtained from the distal great cardiac vein (GCV), and radiofrequency (RF) delivery eliminated the PVC and VT. However, the PVC recurred four times upon cessation of RF delivery. By placing an ablation catheter at the LCC, we obtained pace-mapping showing two different types of QRS morphologies; one was an rS pattern in V1, and the other was an R pattern in V1 with a longer stimulus to QRS interval, which was a nearly perfect match to the PVC. RF application to the LCC permanently eliminated PVCs and VTs. Several VTs from the epicardial LVOT can be cured by RF application from both the distal GCV and the LCC.

Electrophysiological properties of the superior vena cava and venoatrial junction in patients with atrial fibrillation: relevance to catheter ablation.

BACKGROUND: Although the superior vena cava (SVC) has been well known to be one of the important foci triggering atrial fibrillation (AF), its electrophysiological characteristics have received little research attention. The aim of this study was to investigate the electrophysiological properties of the SVC and venoatrial junction (VAJ). METHODS: Twenty-five consecutive AF patients without structural heart disease undergoing electrical SVC isolation were included in this study. After pulmonary vein isolation, a circular decapolar catheter and 2 multipolar catheters were emplaced in the VAJ, right atrial appendage (RAA), and SVC, respectively. Burst pacing and single extrastimulus were applied from the RAA and SVC. The atrial and caval potentials on the circular catheter in the VAJ were investigated. RESULTS: Intracaval conduction delay and various degrees of conduction block over the VAJ were observed with burst pacing from both the RAA and SVC. A single extrastimulus from the RAA and SVC with a basic cycle length of 600 milliseconds prolonged the conduction time via the VAJ by 81 ± 49.7 milliseconds and 61 ± 58.7 milliseconds, respectively. The atrial and caval electrograms at the VAJ, which were separated from each other by pacing applications, facilitated mapping of the earliest activation site at the VAJ. CONCLUSIONS: Intracaval conduction delay and decremental conduction property via the VAJ were demonstrated using pacing maneuvers. Pacing applications from the RAA or SVC can help distinguish the atrial and caval potentials and can facilitate mapping of the optimal ablation sites to isolate the SVC.

Nonthermal cardiac catheter ablation using photodynamic therapy.

BACKGROUND: Radiofrequency ablation has limitations, largely related to creation of lesions by heating. Here, we report the first nonthermal ablation by applying photodynamic therapy (PDT) to cardiac tissues using a custom-made deflectable laser catheter. The present study investigated the feasibility of PDT for cavotricuspid isthmus ablation in a canine model. METHODS AND RESULTS: We evaluated the pharmacokinetic profiles of 17 canines after administration of a photosensitizer (talaporfin sodium) by various protocols. We succeeded in maintaining the photosensitizer concentration at a level in excess of the clinically effective dose for humans. Using a 4-polar 7-French deflectable laser catheter, we performed PDT-mediated cavotricuspid isthmus ablation in 8 canines. PDT caused oxidative injury only to the irradiated area and successfully produced a persistent electric conduction block. No acute, gross changes such as edematous degeneration, thrombus formation, steam pops, or traumatic injury were observed after irradiation. Hematoxylin and eosin staining of tissues samples also showed well-preserved endothelial layers. Testing of the blood samples taken before and after the procedure revealed no remarkable changes. Lesion size at 2 weeks after the procedure and the temperature data collected during irradiation were compared between the PDT and irrigated radiofrequency ablation procedures. A ventricular cross-section revealed a solid PDT lesion, which was as deep as a radiofrequency lesion. In addition, endocardial, surficial, and intramural temperature monitoring during the PDT irradiation clearly demonstrated the nonthermal nature of the ablation technique. CONCLUSIONS: Nonthermal PDT-mediated catheter ablation is a potentially novel treatment for cardiac arrhythmias.

Ventricular fibrillation associated with J-wave manifestation following pericarditis after catheter ablation for paroxysmal atrial fibrillation.

We present a patient with ventricular fibrillation (VF) associated with J-wave manifestation following pericarditis after catheter ablation of paroxysmal atrial fibrillation (AF). The premature ventricular contraction induced VF with J-waves in the inferior leads 2 days after the procedure. The patient's juvenile onset of AF and a family history of sudden cardiac death strongly suggested an underlying hereditable channelopathy. The late gadolinium enhancement in the posterior wall, viewed by cardiac magnetic resonance imaging, matched the leads of the J-waves. VF might develop in juvenile onset of AF especially in individuals with a family history of sudden cardiac death.

Ridge-related reentry: a variant of perimitral atrial tachycardia.

INTRODUCTION: The ridge between the left pulmonary veins (PV) and the left atrial appendage composes part of the lateral mitral isthmus (LMI). Following circumferential PV isolation and LMI linear ablation for the treatment of atrial fibrillation (AF), a critical pathway might develop over the ridge leading to a ridge-related reentry (RRR). METHODS AND RESULTS: Out of 61 patients who underwent circumferential PV isolation appended by LMI ablation, 5 patients developed RRR. The diagnosis of RRR was based on (1) macro-reentrant atrial tachycardia involving the septum, anterior and inferior wall of the left atrium; (2) slow conduction along the ridge; (3) wide-split double potentials in the ventricular aspect of the LMI were identified with the coronary sinus (CS) electrodes. RRR was investigated with electroanatomical mapping and entrainment mapping and catheter ablation was carried out in all patients. The mean cycle length (CL) of RRR was 312 ± 82 milliseconds and the PPIs at the left atrial septum, inferior and anterior wall during RRR were 10 ± 6, 12 ± 8, 9 ± 5 milliseconds longer than the RRR CL. The interval of the double potentials recorded in the CS electrodes crossing the LMI was 164 ± 38 milliseconds during RRR and the PPI on the LMI near the mitral annulus was 57 ± 10 milliseconds longer than the RRR CL. Catheter ablation was performed anatomically by targeting the ridge and successfully terminated RRR. CONCLUSION: After circumferential PV isolation and ablation for LMI in patients with AF, RRR can develop by utilizing the surviving myocardial tissue of the ridge as a critical pathway.

Ventricular fibrillation associated with complete right bundle branch block.

BACKGROUND: A substantial number of patients with idiopathic ventricular fibrillation (IVF) present with no specific electrocardiographic (ECG) findings. OBJECTIVE: To evaluate complete right bundle branch block (RBBB) in patients with IVF. METHODS: Patients with IVF showing complete RBBB were included in the present study. Structural and primary electrical diseases were excluded, and provocation tests were performed to exclude the presence of spastic angina or Brugada syndrome (BrS). The prevalence of complete RBBB and the clinical and ECG parameters were compared either in patients with IVF who did not show RBBB or in the general population and age and sex comparable controls with RBBB. RESULTS: Of 96 patients with IVF, 9 patients were excluded for the presence of BrS. Of 87 patients studied, 10 (11.5%) patients showed complete RBBB. None had structural heart diseases, BrS, or coronary spasms. The mean age was 44 ± 15 years, and 8 of 10 patients were men. Among the ECG parameters, only the QRS duration was different from that of the other patients with IVF who did not show complete RBBB. Ventricular fibrillation recurred in 3:2 in the form of storms, which were well suppressed by isoproterenol. Complete RBBB was found less often in control subjects (1.37%; P < .0001), and the QRS duration was more prolonged in patients with IVF: 139 ± 10ms vs 150 ± 14ms (P = .0061). CONCLUSIONS: Complete RBBB exists more often in patients with IVF than in controls. A prolonged QRS complex suggests a conduction abnormality. Our findings warrant further investigation of the role of RBBB in the development of arrhythmias in patients with IVF.

Three-dimensional imaging and mapping of the right and left phrenic nerves: relevance to interventional cardiovascular therapy.

AIMS: Phrenic nerves (PNs) can be damaged during interventional cardiovascular therapy because of the nerves' proximity to the heart. This study aimed to analyse the anatomy of the PN by performing three-dimensional (3-D) imaging and pace mapping. METHODS AND RESULTS: Forty consecutive patients with atrial fibrillation referred for catheter ablation were enrolled in this study and underwent preoperative cardiovascular computed tomography (CT). In 10 patients with sinus rhythm during tomography, 3-D images of the right and left pericardiophrenic bundles (PBs), consisting of the ipsilateral PN and accompanying vessels, were reconstructed from the CT data. During the electrophysiological study, PN pace mapping was performed from both atria. The course of the PBs generated by CT imaging and the PN pace map generated by the 3-D mapping system were compared. By electrical pacing, the PNs were captured in 40 individuals (100%) from the superior vena cava and the right atrium, and in 17 patients (43%) from the left atrial appendage. Clear 3-D images of PBs were reconstructed in all cases in which CT-reconstruction was performed. The distance between the locations of the right PB generated by CT imaging and those of the right PN-capture sites in the right-sided heart on the mapping system was 8.7 ± 5.8 mm. CONCLUSIONS: The 3-D routes of the bilateral PNs passing near the heart were verified by pace mapping. The preoperatively reconstructed 3-D course of the PB succeeded in locating the PN, which may facilitate the comprehension of PN anatomy to avoid its injury during interventional cardiovascular therapy.

Sudden cardiac arrest and syncope triggered by coronary spasm.

BACKGROUND: Patients with coronary spasm generally have a good prognosis, although it can result in sudden cardiac arrest (SCA) and syncope. We hypothesized that the nature of coronary spasm triggering lethal arrhythmias may be different from that which induces angina-only. METHODS: Clinical characteristics were examined in patients who had experienced SCA (n = 18) or syncope (n = 28) triggered by coronary spasm. These characteristics were compared to those of patients who had coronary spastic angina-only (n = 52). RESULTS: SCA and syncope occurred frequently during daytime in 57% and 68%, respectively. Spontaneous ST-segment changes during daytime were recorded more often in patients with SCA (50%) and syncope (39%) than angina-only patients (4%, p < 0.01 for each). Nocturnal angina occurred less frequently in patients with SCA (33%) and syncope (32%) than angina-only patients (83%, p < 0.01 for each). Severe multivessel spasm, daytime ST-segment changes, and younger age were significant predictors of SCA. Daytime ST-segment changes and active smoking were related to syncope. CONCLUSIONS: The circadian variance of coronary spasm triggering SCA or syncope may be different from that inducing typical coronary spastic angina. The coronary spasm should be evaluated for patients with aborted SCA or recurrent syncope of unknown cause, even though the patients have not experienced the typical nocturnal angina.

The effectiveness of rigid pericardial endoscopy for minimally invasive minor surgeries: cell transplantation, epicardial pacemaker lead implantation, and epicardial ablation.

BACKGROUND: The efficacy and safety of rigid pericardial endoscopy as the promising minimally invasive approach to the pericardial space was evaluated. Techniques for cell transplantation, epicardial pacemaker lead implantation, and epicardial ablation were developed. METHODS: Two swine and 5 canines were studied to evaluate the safety and efficacy of rigid pericardial endoscopy. After a double pericardiocentesis, a transurethral rigid endoscope was inserted into the pericardial space. The technique to obtain a clear visual field was examined, and acute complications such as hemodynamic changes and the effects on intra-pericardial pressure were evaluated. Using custom-made needles, pacemaker leads, and forceps, the applications for cell transplantation, epicardial pacemaker lead implantation, and epicardial ablation were also evaluated. RESULTS: The use of air, the detention of a stiff guide wire in the pericardial space, and the stretching of the pericardium with the rigid endoscope were all useful to obtain a clear visual field. A side-lying position also aided observation of the posterior side of the heart. As a cell transplantation methodology, we developed an ultrasonography-guided needle, which allows for the safe visualization of transplantation without major complications. Pacemaker leads were safely and properly implanted, which provides a better outcome for cardiac resynchronizing therapy. Furthermore, the success of clear visualization of the pulmonary veins enabled us to perform epicardial ablation. CONCLUSIONS: Rigid pericardial endoscopy holds promise as a safe method for minimally invasive cell transplantation, epicardial pacemaker lead implantation, and epicardial ablation by allowing clear visualization of the pericardial space.

Electrical isolation of the superior vena cava using upstream phrenic pacing to avoid phrenic nerve injury.

BACKGROUND: Phrenic nerve (PN) injury is a potential complication that can occur during superior vena cava (SVC) isolation to cure atrial fibrillation (AF). Avoiding radiofrequency (RF) energy delivery is the safer alternative but may result in failed isolation. High-output PN pacing above the ablation site (upstream PN pacing) to confirm whether the PN is intact is a promising technique to avoid PN injury. This study was conducted to elucidate the safety of delivering RF energy at the site of capture of the right PN using upstream high-output pacing during electrical SVC isolation. METHODS: SVC isolation was conducted in 41 drug-resistant AF patients. When high-output pacing (25 mA) from the distal tip of the ablation catheter captured the PN at the right atrial-SVC junction, upstream PN pacing (cycle length: 1000-1500 ms) was applied during RF delivery. The application of RF energy was stopped upon the failure or weakness of diaphragmatic twitching. The feasibility of SVC isolation using upstream PN pacing was investigated. RESULTS: In all 41 patients, SVC isolation was successfully achieved. RF energy was delivered at the PN capture site in 26 patients (154 ± 138 second, 18 ± 5 W), and upstream PN pacing was successfully applied in all of the patients. Out of 46 SVC isolations, including five repeated sessions, PN injury occurred in one patient, who recovered spontaneously within 2 weeks. CONCLUSIONS: Upstream PN pacing may be effective for the safe completion of SVC isolation and to reduce the severity of PN injury.

Study of blood charring precursor states using backscattering at 663 nm from blood and optical window boundary.

BACKGROUND AND OBJECTIVE: Contact laser irradiation is generally used in therapeutic laser procedures such as plastic surgery and laser catheter lead removal. However, it may induce blood charring on the surface of the optical window in blood circumstance so that the laser beam might be blocked. Various charring detection methods have been proposed, but they detect charring only after charring has occurred. This study investigates the transient behavior of red blood cells (RBCs) prior to the charring on the surface of an optical window during red laser irradiation in blood circumstance. MATERIALS AND METHODS: The backscattering light power was continuously measured to investigate the transient behavior of a 1-mm-thick porcine blood model (hematocrit: 40%) during continuous laser irradiation (center wavelength: 663 nm; irradiance: 81 W/cm(2)). A rabbit blood model was microscopically observed after irradiation. The absorption coefficient (µ(a)) and the reduced scattering coefficient (µ'(s)) were measured using a double integrating sphere setup and the inverse adding-doubling method. The backscattering light power was continuously measured in vivo during contact laser irradiation via a laser catheter in a porcine heart cavity. RESULTS: The results reveal that it may be possible to detect a precursory state of charring from a time course of the backscattering light power. µ(a) increased monotonically by 15% until charring occurred. µ'(s) decreased by 10% followed a broad peak until charring occurred. These changes in the optical property correspond to changes in the morphology of RBCs. Changes in the backscattering light power measured in vivo were similar to those measured ex vivo. CONCLUSIONS: The transient optical changes in blood prior to charring may be caused by changes in the morphology of RBCs on the optical window surface. Backscattering light power measurements may be a practical method to detect the precursor state of charring.

Disease characterization using LQTS-specific induced pluripotent stem cells.

AIMS: Long QT syndrome (LQTS) is an inheritable and life-threatening disease; however, it is often difficult to determine disease characteristics in sporadic cases with novel mutations, and more precise analysis is necessary for the successful development of evidence-based clinical therapies. This study thus sought to better characterize ion channel cardiac disorders using induced pluripotent stem cells (iPSCs). METHODS AND RESULTS: We reprogrammed somatic cells from a patient with sporadic LQTS and from controls, and differentiated them into cardiomyocytes through embryoid body (EB) formation. Electrophysiological analysis of the LQTS-iPSC-derived EBs using a multi-electrode array (MEA) system revealed a markedly prolonged field potential duration (FPD). The IKr blocker E4031 significantly prolonged FPD in control- and LQTS-iPSC-derived EBs and induced frequent severe arrhythmia only in LQTS-iPSC-derived EBs. The IKs blocker chromanol 293B did not prolong FPD in the LQTS-iPSC-derived EBs, but significantly prolonged FPD in the control EBs, suggesting the involvement of IKs disturbance in the patient. Patch-clamp analysis and immunostaining confirmed a dominant-negative role for 1893delC in IKs channels due to a trafficking deficiency in iPSC-derived cardiomyocytes and human embryonic kidney (HEK) cells. CONCLUSIONS: This study demonstrated that iPSCs could be useful to characterize LQTS disease as well as drug responses in the LQTS patient with a novel mutation. Such analyses may in turn lead to future progress in personalized medicine.

Autoimmunity against M2muscarinic acetylcholine receptor induces myocarditis and leads to a dilated cardiomyopathy-like phenotype.

Patients with dilated cardiomyopathy (DCM) often have autoantibodies against cardiac antigens including the M(2) muscarinic acetylcholine receptor (M(2)R). To elucidate the role of autoimmunity against M(2)R in disease development, we induced an immune response against M(2)R by adoptive transfer into Rag2(-/-) mice of splenocytes from M(2)R(-/-) mice immunized with a recombinant M(2)R protein. T lymphocytes transiently infiltrated the heart in recipient mice followed by morphological changes in cardiomyocytes. These mice produced IgG antibodies against M(2)R, which bound to cardiomyocytes in vivo and decreased the amplitude of calcium signals in isolated rat cardiomyocytes in vitro. Recipient mice showed increased heart weights associated with increased intraventricular diameter, decreased systolic function, and increased action potential duration, which are characteristics of DCM. Our results suggest that myocarditis and DCM associated with the presence of anti-M(2)R antibodies are autoimmune diseases with a risk of progressing to the terminal stage. Our mouse model will be useful in the analysis of the molecular mechanisms of disease progression and the development of new therapies for DCM.

Myocardial electrical conduction block induced by photosensitization reaction in exposed porcine hearts in vivo.

BACKGROUND AND OBJECTIVE: This study proposes photosensitization reaction for non-thermal cardiac ablation in arrhythmia therapy. Acute and chronic phase experiments were conducted in exposed porcine hearts to demonstrate the photosensitization reaction-induced myocardial electrical conduction block in vivo. STUDY DESIGN/MATERIALS AND METHODS: The porcine left atrial appendage was exposed under an open-chest procedure. Then, a water-soluble chlorin photosensitizer, NPe6, was injected into the pigs intravenously at 5 or 10 mg/kg. About 15 or 30 minutes after the injection, a 663-nm continuous-wave diode laser was irradiated on the surface of the atrial appendage through a silica optical fiber. The laser energy was delivered to the tissue point by point at an energy density of 50-208 J/cm(2). RESULTS: Acute and chronic tissue damages as a result of the photosensitization reaction were determined by electrophysiology and histology, respectively. The change in the myocardial conduction time between two electrodes was measured immediately after the completion of the 35-mm irradiation line between the electrodes. The conduction delay of 35.5 milliseconds might be due to the change in the conduction pathway induced by transmural acute conduction block with the photosensitization reaction. The tissue temperature increase in the irradiated area was approximately 12.8°C. Azan-staining revealed about 1-mm transmural fibrosis of the atrial appendage at 2 weeks after the irradiation (50 J/cm(2)). CONCLUSIONS: The results suggest that the photosensitization reaction might induce acute and chronic myocardial electrical conduction block. Cardiac ablation with the photosensitization reaction might be a non-temperature-mediated methodology for arrhythmia therapy.

Treatment of human mesenchymal stem cells with angiotensin receptor blocker improved efficiency of cardiomyogenic transdifferentiation and improved cardiac function via angiogenesis.

To improve the modest efficacy of mesenchymal stem cell (MSC) transplantation, the treatment of human MSCs with angiotensin receptor blockers (ARBs) was investigated. MSCs were cultured with or without the medium containing 3 µmol/l of ARBs before cardiomyogenic induction. After cardiomyogenic induction in vitro, cardiomyogenic transdifferentiation efficiency (CTE) was calculated by immunocytochemistry using anticardiac troponin-I antibody. In the nude rat chronic myocardial infarction model, we injected MSCs pretreated with candesartan (A-BM; n = 18) or injected MSCs without pretreatment of candesartan (BM; n = 25), each having survived for 2 weeks. The left ventricular function, as measured by echocardiogram, was compared with cardiomyogenic transdifferentiation in vivo, as determined by immunohistochemistry. Pretreatment with ARBs significantly increased the CTE in vitro (10.1 ± 0.8 n = 12 vs. 4.6 ± 0.3% n = 25, p < .05). Transplantation of candesartan-pretreated MSCs significantly improved the change in left ventricular ejection fraction (BM; -7.2 ± 2.0 vs. A-BM; 3.3 ± 2.3%). Immunohistochemistry revealed significant improvement of cardiomyogenic transdifferentiation in A-BM in vivo (BM; 0 ± 0 vs. A-BM; 0.014 ± 0.006%). Transplantation of ARB-pretreated MSCs significantly improved cardiac function and can be a promising cardiac stem cell source from which to expect cardiomyogenesis.