Namsik Yoon

Beneficial effects of an angiotensin‑II receptor blocker on structural atrial reverse‑remodeling in a rat model of ischemic heart failure

The remodeling of gap junctions may affect their conduction properties and contribute to the maintenance of atrial fibrillation. The significance of the role of angiotensin-II receptor blockers (ARBs) in upstream therapy is not clear. This study was performed to investigate the effects of ARBs on atrial remodeling in a heart failure model. A model of heart failure was established or sham surgery performed in 24 Sprague-Dawley male rats. The rats were divided into sham, heart failure and heart failure-ARB groups. In the ARB group, 30 mg/kg of losartan was administered each day for 4 weeks. Echocardiography was performed at the baseline and 4 weeks following the surgery. An atrial fibrillation induction study and histological and immunohistochemical evaluation were performed 4 weeks after surgery. The increase in the left atrial diameter of the heart failure-ARB group was smaller than that of the heart failure group (P=0.028). The atrial fibrillation inducibility and duration of induced atrial fibrillation were not different between the heart failure and heart failure-ARB groups. Masson’s trichrome staining revealed less fibrosis in the heart failure-ARB group compared with the heart failure group. Immunohistochemical staining and western blot analysis for connexin 43 showed a lower expression level in the heart failure-ARB group compared with that in the heart failure group. In a rat model of ischemic heart failure the ARB losartan had structural and histological atrial reverse-remodeling effects. However, its role as an electrical stabilizer requires further study.

Mechanisms Underlying Epicardial Radiofrequency Ablation to Suppress Arrhythmogenesis in Experimental Models of Brugada Syndrome

OBJECTIVES This study sought to test the hypothesis that elimination of sites of abnormal repolarization, via epicardial RFA, suppresses the electrocardiographic and arrhythmic manifestations of BrS. BACKGROUND Brugada syndrome (BrS) is associated with ventricular tachycardia and ventricular fibrillation leading to sudden cardiac death. Nademanee et al. reported that radiofrequency ablation (RFA) of right ventricular outflow tract epicardium significantly reduced the electrocardiogram and arrhythmic manifestations of BrS. These authors concluded that low-voltage fractionated electrogram activity and late potentials are caused by conduction delay within the right ventricular outflow tract and that the ameliorative effect of RFA is caused by elimination of this substrate. Szel et al. recently demonstrated that the abnormal electrogram activity is associated with repolarization defects rather than depolarization or conduction defects. METHODS Action potentials (AP), electrograms, and pseudoelectrocardiogram were simultaneously recorded from coronary-perfused canine right ventricular wedge preparations. Two pharmacological models were used to mimic BrS genotype: combination of INa blocker ajmaline (1 to 10 μM) and IK-ATP agonist pinacidil (1 to 5 μM); or combination of Ito agonist NS5806 (4 to 10 μM) and ICa blocker verapamil (0.5 to 2 μM). After stable induction of abnormal electrograms and arrhythmic activity, the preparation was mapped and epicardial RFA was applied. RESULTS Fractionated low-voltage electrical activity was observed in right ventricular epicardium but not endocardium as a consequence of heterogeneities in the appearance of the second upstroke of the epicardial AP. Discrete late potentials developed as a result of delay of the second upstroke of the AP and of concealed phase 2 re-entry. Epicardial RFA of these abnormalities normalized Brugada pattern and abolished arrhythmic activity, regardless of the pharmacological model used. CONCLUSIONS Our results suggest that epicardial RFA exerts its ameliorative effect in the setting of BrS by destroying the cells with the most prominent AP notch, thus eliminating sites of abnormal repolarization and the substrate for ventricular tachycardia ventricular fibrillation.

Radiodensity on serial chest X-rays for the diagnosis of foreign body aspiration in children

ObjectivesTo evaluate the utility of measuring lung radiodensity from chest X-ray for the diagnosis of foreign body aspirationMethodsRecords of 59 children with foreign body aspiration were retrospectively reviewed. Lung radiodensity and radiodensity ratio (right/left lung radio density) before and after foreign body removal were measured. Radiodensity was calculated as the relative score compared with the tenth thoracic vertebra body (100 points) and the background (0 point). The change of radiodensity ratio (difference in radiodensity ratio of the second X-ray from that of first X-ray) was compared between 22 patients (foreign body group) and 22 normal subjects (control group).ResultsIn the group of foreign body in the left bronchus, the mean (SD) radiodensity of the left lung [53.5 (12.8)] was lower than that of the right lung [60.8 (7.7), P<0.01] and it increased after foreign body removal [60.0 (6.9), P=0.02]. The radiodensity ratio decreased from 1.20 (0.30) to 0.96 (0.09) (P<0.01) after foreign body removal. In the group with a foreign body in the right bronchus, the radiodensity of the right lung [51.8 (12.8)] was lower than that of left lung [62.0 (11.7), P=0.03], and it also increased after foreign body removal [58.4 (9.6), P=0.03]. The change of radiodensity ratio in the foreign body group [15.7 (17.8)%] was higher than the control group [5.4 (4.3)%, P=0.01] and the cutoff value was 7.5%.ConclusionRadiodensity from chest X-ray could be a useful tool for diagnosing foreign body aspiration in children.

Preventive Effects of the Angiotensin-II Receptor Blocker on Atrial Remodeling in an Ischemic Heart Failure Model of Rats

Background and Objectives It is widely known that angiotensin-II receptor blockers (ARBs) have reverse remodeling effects in atrium. Although atrial fibrillation is frequent in ischemic heart failure clinically, experiments to demonstrate ARBs effects on atrial remodeling in a heart failure model are rare. Materials and Methods A heart failure model and a sham-operated group were formed in 25 Sprague-Dawley male rats of roughly 260 g in weight. Ischemic heart failure models were obtained via ligation of the left anterior descending coronary artery. In the ARB group, 30 mg/kg of losartan was administrated over a day for 4 weeks. Echocardiography was performed to measure left ventricle ejection fraction and left atrial diameter (LAD) at the baseline and 4 weeks after the operation. 4 weeks later, histologic and immunohistochemical evaluation were performed. Results Groups were divided into the sham group, heart failure group, and heart failure-ARB group. We maintained 5 rats in each group for 4 weeks after operation. The decrease of left ventricular ejection fraction in the heart failure-ARB group was less than that in the heart failure group (p=0.023). The increase of LAD in the heart failure-ARB group was less than that in the heart failure group (p=0.025). Massons trichrome stain revealed less fibrosis in the heart failure-ARB group. Immunohistochemical stain and western blot for connexin 43 showed less expression in the heart failure-ARB group. Conclusion In the ischemic heart failure model of rats, structurally and histologically, the ARB, losartan, has atrial reverse-remodeling effects. However, electrically, its role as an electrical stabilizer should be studied further.

Clinical Utility of Echocardiography for the Diagnosis and Prognosis in Children with Bronchopulmonary Dsyplasia

Background Bronchopulmonary dysplasia (BPD) may result in chronic pulmonary artery hypertension and right ventricular (RV) dysfunction. Various echocardiographic assessments of RV dysfunction have been used to determine whether echocardiographic measurements of premature infants with BPD could provide sensitive measures of RV function that correlates with BPD severity. Methods Twenty-eight control subjects without BPD (non BPD group), 28 patients with mild BPD, 11 patients with moderate BPD, and six patients with severe BPD underwent echocardiograms with standard measurement such as ejection fraction by M-mode, tricuspid regurgitation pressure gradient, myocardial performance index (MPI) derived from pulse Doppler, and tissue Doppler imaging (TDI) measurements. BPD severity was classified by the NICHD/NHLBI/ORD workshop rating scale. Twenty-eight control subjects without BPD (non BPD group), 28 patients with mild BPD, 11 patients with moderate BPD, and six patients with severe BPD underwent echocardiograms with standard measurement such as ejection fraction by M-mode, tricuspid regurgitation pressure gradient, myocardial performance index (MPI) derived from pulse Doppler, and TDI measurements. BPD severity was classified by the NICHD/NHLBI/ORD workshop rating scale. Results None of the standard echocardiographic findings was significantly different between the control group and BPD groups. However, mean septal TDI-MPI of the severe BPD group (0.68 ± 0.06) was significantly (p < 0.01) higher than that of the non-BPD (0.58 ± 0.10) or the mild BPD group (0.59 ± 0.12). In addition, mean RV TDI-MPI of the severe BPD group (0.71 ± 0.13) was significantly (p < 0.05) higher than that of the non-BPD group (0.56 ± 0.08) or the mild BPD group (0.60 ± 0.125). Linear regression showed a good correlation between the severity of BPD and RV TDI-MPI (p = 0.01, R = 0.30) or septal TDI-MPI (p = 0.04, R = 0.24). Conclusion Echocardiographic evaluation of RV function based on an assessment of RV TDI-MPI can provide RV dysfunction parameter in premature infants with BPD.

T peak–Tend interval during therapeutic hypothermia can predict upcoming ventricular fibrillation in subjects with aborted arrhythmic sudden cardiac death: 3-years follow-up results

Aims Prolonged Tpeak-Tend interval has been shown to be markers of arrhythmogenesis in various cardiac disorders. However, its dynamicity is one of the obstacles to predict fatal ventricular arrhythmia. This study investigated whether Tpeak-Tend interval during therapeutic hypothermia (TH) is associated with ventricular fibrillation (VF) inducibility and clinical arrhythmia in subjects with aborted arrhythmic sudden cardiac death (SCD). Methods and results The study group included 31 patients (24 males, age 39.1 ± 17.6 years) presenting with arrhythmic SCD in whom Tpeak-Tend interval and J-wave amplitude were measured in electrocardiogram (ECG) of the earliest medical contact and during TH; these patients underwent programmed ventricular stimulation. The summation of J-wave amplitude and QTc interval increased during TH. However, it was not associated with VF inducibility. Patients with inducible VF showed a small Tpeak-Tend interval dispersion in the baseline 12-lead ECG (68.8 ± 24.7 vs. 94.0 ± 55.6 ms, P = 0.044) and a marked increase of the dispersion during the TH (36.2 ± 51.2 vs. -6.1 ± 45.5 ms, P = 0.039). Twenty-four patients underwent implantable cardioverter defibrillator (ICD) implantation. Among them, the patients with long QTc, Tpeak-Tend, and precordial Tpeak-Tend during the TH developed VF more frequently (QTc, 511.9 ± 53.71 ms vs. 566.5 ± 56.08 ms, P = 0.038; Tpeak-Tend interval, 145.6 ± 38.4 ms vs. 185.7 ± 49.95 ms, P = 0.048; precordial Tpeak-Tend interval, 139.3 ± 35.11 ms vs. 185.7 ± 49.95 ms, P = 0.018). The initial VF inducibility was not related with the VF development in follow-up. Conclusion In patients with aborted arrhythmic SCD, long Tpeak-Tend interval and QTc interval during TH could predict VF development in their follow-up.