Toyonobu Tsuda

Functional Characterization of Rare Variants Implicated in Susceptibility to Lone Atrial Fibrillation

Background—Few rare variants in atrial fibrillation (AF)–associated genes have been functionally characterized to identify a causal relationship between these variants and development of AF. We here sought to determine the clinical effect of rare variants in AF-associated genes in patients with lone AF and characterized these variants electrophysiologically and bioinformatically. Methods and Results—We screened all coding regions in 12 AF-associated genes in 90 patients with lone AF, with an onset of 47±11 years (66 men; mean age, 56±13 years) by high-resolution melting curve analysis and DNA sequencing. The potassium and sodium currents were analyzed using whole-cell patch clamping. In addition to using 4 individual in silico prediction tools, we extended those predictions to an integrated tool (Combined Annotation Dependent Depletion). We identified 7 rare variants in KCNA5, KCNQ1, KCNH2, SCN5A, and SCN1B genes in 8 patients: 2 of 8 probands had a family history of AF. Electrophysiological studies revealed that 2 variants showed a loss-of-function, and 4 variants showed a gain-of-function. Five of 6 variants with electrophysiological abnormalities were predicted as pathogenic by Combined Annotation Dependent Depletion scores. Conclusions—In our cohort of patients with lone AF, 7 rare variants in cardiac ion channels were identified in 8 probands. A combination of electrophysiological studies and in silico predictions showed that these variants could contribute to the development of lone AF, although further in vivo study is necessary to confirm these results. More than half of AF-associated rare variants showed gain-of-function behavior, which may be targeted using genotype-specific pharmacological therapy.

Impact of Systolic Dysfunction in Genotyped Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a disease of the sarcomere, and approximately 5% of cases of HCM show systolic dysfunction with poor prognosis. Few data exist regarding the systolic dysfunction in a large population of genotyped HCM subjects.

A novel mutation in the transmembrane nonpore region of the KCNH2 gene causes severe clinical manifestations of long QT syndrome

BACKGROUND Long QT syndrome (LQTS) is characterized by prolonged ventricular repolarization and variable clinical course with arrhythmia-related syncope and sudden death. Mutations in the nonpore region of the LQTS-associated KCNH2 gene (also known as hERG) are mostly associated with coassembly or trafficking abnormalities, resulting in haplotype insufficiency and milder clinical phenotypes compared with mutations in the pore domain. OBJECTIVE To investigate the effect of a nonpore mutation on the channel current, which was identified from an LQTS family with severe clinical phenotypes. METHODS Two members of a Japanese family with LQTS were searched for mutations in KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, and KCNJ2 genes by using automated DNA sequencing. We characterized the electrophysiological properties and glycosylation pattern of the mutant channels by using patch clamp recording and Western blot analysis. RESULTS In the LQTS patient with torsades de pointes and cardiopulmonary arrest, we identified the novel T473P mutation in the transmembrane nonpore region of KCNH2. The probands father carried the same mutation and showed prolonged corrected QT interval and frequent torsades de pointes in the presence of hypokalemia following the administration of garenoxacin. Patch clamp analysis in heterologous cells showed that hERG T473P channels generated no current and exhibited a dominant negative effect when coexpressed with wild-type protein. Only incompletely glycosylated hERG T473P channels were observed by using Western blot analysis, suggesting impaired trafficking. CONCLUSIONS These results demonstrated that a trafficking-deficient mutation in the transmembrane nonpore region of KCNH2 causes a dominant negative effect and a severe clinical course in affected patients.

Impact of T wave amplitude in lead aVR on predicting cardiac events in ischemic and nonischemic cardiomyopathy patients with an implantable cardioverter defibrillator

T wave amplitudes during ventricular repolarization in the lead aVR (TAaVR) are shown to be associated with adverse cardiac events in patients with several cardiovascular diseases, such as postmyocardial infarction. However, the utility of TAaVR has not been previously evaluated in patients with cardiomyopathy who have received implantable cardioverter defibrillators (ICD). Patients with ischemic or nonischemic cardiomyopathy (ICM or NICM, respectively) and who received an ICD may experience worsening of their condition due to the introduction of electric shock during treatment. This study aimed to investigate the utility of TAaVR in the prediction of cardiac events in ICM or NICM patients with ICD.

Severe mitral regurgitation due to rupture of mitral valve chordae tendineae in a patient with Graves disease

Abstract Mitral valve prolapse is a common disorder, but severe mitral regurgitation (MR) as a result of rupture of mitral valve chordae tendineae is a rare manifestation of thyrotoxic heart disease. There are limited reports with respect to the onset of severe MR as a complication of Graves disease. We report a case of a 60-year-old woman with Graves disease and thyroid-associated ophthalmopathy as her past history. She had signs of congestive heart failure, a loud murmur as a result of MR, clinical cardiomegaly, and peripheral edema. Echocardiographic and angiographic data were consistent with moderate to severe MR. She also had thyrotoxicosis caused by the recurrence of Graves disease. She was taking methiamazole, a beta-blocker, hydrocortisone, and potassium iodide. Ultimately, thyroidectomy was performed to improve her hyperthyroid state. After normalization of her thyroid status, she continued to have moderate to severe MR, and mitral valve repair was performed. The present case had severe MR as a result of rupture of mitral valve chordae tendineae, which is considered rare in a patient with Graves disease.

Amiodarone-induced reversible and irreversible hepatotoxicity: two case reports

BackgroundAmiodarone is a highly effective treatment for supraventricular and ventricular tachyarrhythmia; however, it could be associated with several serious adverse effects, including liver injury.Case presentationWe report the clinical and histological features of two contrasting Japanese patients with amiodarone-induced reversible and irreversible hepatotoxicity. One patient with amiodarone-induced irreversible hepatotoxicity showed liver cirrhosis during treatment with amiodarone and died of hepatic failure; the other patient, who had reversible hepatotoxicity, showed a reversible course of liver function and imaging after discontinuation of amiodarone.ConclusionsWe emphasize the importance of close monitoring of liver enzymes and evaluation of liver computed tomographic imaging as well as liver biopsy during treatment with amiodarone, and discontinuation should be considered when amiodarone-induced hepatotoxicity is suspected.

Functional analysis of KCNH2 gene mutations of type 2 long QT syndrome in larval zebrafish using microscopy and electrocardiography

Heterologous expression systems play a vital role in the characterization of potassium voltage-gated channel subfamily H member 2 (KCNH2) gene mutations, such as E637K which is associated with long QT syndrome type 2 (LQT2). In vivo assays using zebrafish provide a means for testing genetic variants of cardiac disease; however, limited information on the role of the E637K mutation is available from in vivo systems and their utility has yet to be fully exploited in the context of LQT2. We sought to evaluate the ability of the E637K mutant channel to restore normal repolarization in larval zebrafish with a human KCNH2 orthologue, kcnh2a-knockdown. A morpholino (MO) targeting kcnh2a was injected alone or with wild type (WT) or E637K KCNH2 cRNA into zebrafish embryos at the 1–2 cell stage. Cardiac repolarization phenotypes were screened using light microscopy and the QT interval was measured by single lead electrocardiograph (ECG) analysis at 72-h post-fertilization. In the MO alone group, 17% of zebrafish had a normal phenotype; this rate increased to 60% in the WT KCNH2 cRNA injected zebrafish and to 35% in the E637K injected zebrafish. The ECG of larval zebrafish revealed that QTc was significantly prolonged in the MO alone group compared to the control group. Co-injection of WT KCNH2 cRNA shortened the QTc interval, however, that of the E637K did not. We suggest that this in vivo cardiac assay using microscopy and ECG in larval zebrafish offers a reliable approach for risk discrimination of KCNH2 mutations.

Impact of B-Type Natriuretic Peptide Level on Risk Stratification of Thromboembolism and Death in Patients With Nonvalvular Atrial Fibrillation ― The Hokuriku-Plus AF Registry ―

BACKGROUND B-type natriuretic peptide (BNP) may be a predictor of stroke risk in patients with nonvalvular atrial fibrillation (NVAF); because heart failure is associated with the incidence of stroke in AF patients. However, limited data exist regarding the association between BNP at baseline and risks of thromboembolic events (TE) and death in NVAF patients. MethodsandResults We prospectively studied 1,013 NVAF patients (725 men, 72.8±9.7 years old) from the Hokuriku-plus AF Registry to determine the relationship between BNP at baseline and prognosis among Japanese NVAF patients. During the follow-up period (median, 751 days); 31 patients experienced TE and there were 81 cases of TE/all-cause death. For each endpoint we constructed receiver-operating characteristic curves that gave cutoff points of BNP for TE (170 pg/mL) and TE/all-cause death (147 pg/mL). Multivariate analysis with the Cox-proportional hazards model indicated that high BNP was significantly associated with risks of TE (hazard ratio [HR] 3.86; 95% confidence interval [CI] 1.83-8.67; P=0.0003) and TE/all-cause death (HR 2.27; 95% CI 1.45-3.56; P=0.0003). Based on the C-index and net reclassification improvement, the addition of BNP to CHA2DS2-VASc statistically improved the prediction of TE. CONCLUSIONS In a real-world cohort of Japanese NVAF patients, high BNP was significantly associated with TE and death. Plasma BNP might be a useful biomarker for these adverse clinical events.

Ventricular fibrillation associated with dynamic changes in J-point elevation in a patient with silent thyroiditis

A J wave is a common electrocardiographic finding in the general population. Individuals with prominent J waves in multiple electrocardiogram (ECG) leads have a higher risk of lethal arrhythmias than those with low-amplitude J waves. There are few reports about the relationship between thyroid function and J-wave amplitude. We report the case of a 45-year-old man who had unexpected ventricular fibrillation (VF). He had dynamic J-point elevation in multiple ECG leads. Possible early repolarization syndrome was diagnosed. He also had thyrotoxicosis caused by silent thyroiditis, and his J-wave amplitude decreased according to changes in thyroid function because of spontaneous remission of silent thyroiditis. There was a positive correlation between serum triiodothyronine levels and J-wave amplitudes. The findings in case suggested silent thyroiditis may contribute to the occurrence of VF in a patient with dynamic changes in J-point elevation in multiple ECG leads. Thyrotoxicosis is a relatively common endocrine disease; therefore, clinicians should pay attention to J-wave amplitude in the ECG of patients with thyrotoxicosis.

Abrupt progression of ventricular septal perforation after primary angioplasty for acute myocardial infarction

A 61-year-old-man was transferred to our hospital because of progressive heart failure after reperfusion for acute myocardial infarction (MI). When he visited the local hospital with severe chest pain associated with inferior MI, transthoracic echocardiography revealed small ventricular septal perforation (VSP). The patient had emergent coronary angiography, which revealed total occlusion of the mid-portion of the right coronary artery. Primary angioplasty was successful for reperfusion. However, because of hemodynamic instability the patient was transferred to our hospital. Under these conditions, transthoracic echocardiography which was undertaken 3 hours after primary angioplasty, demonstrated progressive enlargement of the VSP probably due to reperfusion injury. The rupture site, which was further enlarged at the time of operation, was repaired using the patch exclusion technique. The patient could discharge without complications. We suggest that primary angioplasty may potentially induce late reperfusion injury in patients with VSP complicating MI.