Mechanisms of fever-induced QT prolongation and torsades de pointes in patients with KCNH2 mutation.

AIMS: Patients with particular mutations of type-2 long QT syndrome (LQT2) are at an increased risk for malignant arrhythmia during fever. This study aimed to determine the mechanism by which KCNH2 mutations cause fever-induced QT prolongation and torsades de pointes (TdP). METHODS AND RESULTS: We evaluated three KCNH2 mutations, G584S, D609G, and T613M, in the Kv11.1 S5-pore region, identified in patients with marked QT prolongation and TdP during fever. We also evaluated KCNH2 M124T and R269W, which are not associated with fever-induced QT prolongation. We characterized the temperature-dependent changes in the electrophysiological properties of the mutant Kv11.1 channels by patch-clamp recording and computer simulation. The average tail current densities (TCDs) at 35°C for G584S, WT+D609G, and WT+T613M were significantly smaller and less increased with rising temperature from 35°C to 40°C than those for WT, M124T, and R269W. The ratios of the TCDs at 40°C to 35°C for G584S, WT+D609G, and WT+T613M were significantly smaller than for WT, M124T, and R269W. The voltage dependence of the steady-state inactivation curve for WT, M124T, and R269W showed a significant positive shift with increasing temperature; however, that for G584S, WT+D609G, and WT+T613M showed no significant change. Computer simulation demonstrated that G584S, WT+D609G, and WT+T613M caused prolonged action potential durations and early afterdepolarization formation at 40°C. CONCLUSION: These findings indicate that KCNH2 G584S, D609G, and T613M in the S5-pore region reduce the temperature-dependent increase in TCDs through an enhanced inactivation, resulting in QT prolongation and TdP at a febrile state in patients with LQT2.

Reduced current density, partially rescued by mexiletine, and depolarizing shift in activation of SCN5A W374G channels as a cause of severe form of Brugada syndrome.

BACKGROUND: SCN5A-related Brugada syndrome (BrS) can be caused by multiple mechanisms including trafficking defects and altered channel gating properties. Most SCN5A mutations at pore region cause trafficking defects, and some of them can be rescued by mexiletine (MEX). OBJECTIVE: We recently encountered symptomatic siblings with BrS and sought to identify a responsible mutation and reveal its biophysical defects. METHODS: Target panel sequencing was performed. Wild-type (WT) or identified mutant SCN5A was transfected into tsA201 cells. After incubation of transfected cells with or without 0.1 mM MEX for 24-36 hr, whole-cell sodium currents (INa ) were recorded using patch-clamp techniques. RESULTS: The proband was 29-year-old male who experienced cardiopulmonary arrest. Later, his 36-year-old sister, who had been suffering from recurrent episodes of syncope since 12 years, was diagnosed with BrS. An SCN5A W374G mutation, located at pore region of domain 1 (D1 pore), was identified in both. The peak density of W374G-INa was markedly reduced (WT: 521 ± 38 pA/pF, W374G: 60 ± 10 pA/pF, p < .01), and steady-state activation (SSA) was shifted to depolarizing potentials compared with WT-INa (V1/2 -WT: -39.1 ± 0.8 mV, W374G: -30.9 ± 1.1 mV, p < .01). Incubation of W374G-transfected cells with MEX (W374G-MEX) increased INa density, but it was still reduced compared with WT-INa (W374G-MEX: 174 ± 19 pA/pF, p < .01 versus W374G, p < .01 versus WT). The SSA of W374G-MEX-INa was comparable to W374G-INa (V1/2 -W374G-MEX: -31.6 ± 0.7 mV, P = NS). CONCLUSIONS: Reduced current density, possibly due to a trafficking defect, and depolarizing shift in activation of SCN5A W374G are underlying biophysical defects in this severe form of BrS. Trafficking defects of SCN5A mutations at D1 pore may be commonly rescued by MEX.

Multiple arrhythmic and cardiomyopathic phenotypes associated with an SCN5A A735E mutation.

BACKGROUND: SCN5A mutations are associated with multiple arrhythmic and cardiomyopathic phenotypes including Brugada syndrome (BrS), sinus node dysfunction (SND), atrioventricular block, supraventricular tachyarrhythmias (SVTs), long QT syndrome (LQTS), dilated cardiomyopathy and left ventricular noncompaction. Several single SCN5A mutations have been associated with overlap of some of these phenotypes, but never with overlap of all the phenotypes. OBJECTIVE: We encountered two pedigrees with multiple arrhythmic phenotypes with or without cardiomyopathic phenotypes, and sought to identify a responsible mutation and reveal its functional abnormalities. METHODS: Target panel sequencing of 72 genes, including inherited arrhythmia syndromes- and cardiomyopathies-related genes, was employed in two probands. Cascade screening was performed by Saner sequencing. Wild-type or identified mutant SCN5A were expressed in tsA201 cells, and whole-cell sodium currents (INa) were recorded using patch-clamp techniques. RESULTS: We identified an SCN5A A735E mutation in these probands, but did not identify any other mutations. All eight mutation carriers exhibited at least one of the arrhythmic phenotypes. Two patients exhibited multiple arrhythmic phenotypes: one (15-year-old girl) exhibited BrS, SND, and exercise and epinephrine-induced QT prolongation, the other (4-year-old boy) exhibited BrS, SND, and SVTs. Another one (30-year-old male) exhibited all arrhythmic and cardiomyopathic phenotypes, except for LQTS. One male suddenly died at age 22. Functional analysis revealed that the mutant did not produce functional INa. CONCLUSIONS: A non-functional SCN5A A735E mutation could be associated with multiple arrhythmic and cardiomyopathic phenotypes, although there remains a possibility that other unidentified factors may be involved in the phenotypic variability of the mutation carriers.

Identification of six novel SCN5A mutations in Japanese patients with Brugada syndrome.

Mutations in SCN5A are linked to Brugada syndrome in approximately 20% of all cases (BrS1). Several dozen distinct SCN5A mutations in BrS1 have been associated with the increased risk of cardiac arrhythmias. However, the genotype-phenotype relationship remains elusive. The current study analyzed the SCN5A gene to elucidate the potential variability of clinical features in Japanese BrS1 subjects. Subjects of the present study included 30 probands (25 male subjects, 45 ± 15 years of age) with Brugada-pattern ECG. Seven patients had been resuscitated from cardiopulmonary arrest (CPA group). Another 10 patients had a history of syncope (Sy group), and 13 more remain asymptomatic (Asy group). We identified 8 different SCN5A mutations, including 6 novel mutations (CPA group: 1/7, Sy group: 3/10, Asy group: 4/13). An A735E mutation (located at segment (S)1 in domain (D)2) was identified in the CPA group. A novel splice acceptor site mutation (c.393-1c>t), which may produce a prematurely truncated protein, was identified in the Sy group. An E1784K mutation (C-terminus) and a novel mutation V1951M (C-terminus) were also identified in the Sy group. Four novel missense mutations, A586T (D1-D2 linker), R689H (D1-D2 linker), S1553R (S1-S2 in D4), and Q1706H (S5-Pore in D4) were identified in the Asy group. These data may help us understand the genetic heterogeneity of BrS1, which is more prevalent in Japanese than in whites and other ethnic groups.

Adaptive Servo-ventilation Therapy Results in the Prevention of Arrhythmias in Patients with Heart Failure Due to Ischemic Heart Disease.

Objective Whether or not adaptive servo-ventilation (ASV) is effective in preventing arrhythmias in patients with heart failure (HF) due to ischemic heart disease (IHD) is unclear. This study estimated the effects of ASV therapy on arrhythmias in patients with HF due to IHD. Methods One hundred and forty-one consecutive hospitalized patients with HF due to IHD (mean age: 74.9±11.9 years old) were retrospectively assessed in this study. Of the 141 patients, 75 were treated with ASV (ASV group), and 66 were treated without ASV (Non-ASV group). We estimated the incidence of arrhythmias, including paroxysmal atrial fibrillation (PAF) and ventricular tachycardia (VT), during one-year follow-up in both groups using multivariable logistic regression models. Results Men accounted for 55.3% of the study population. There were no significant differences in the baseline clinical characteristic data between the ASV and Non-ASV groups with respect to age, sex, heart rate, risk factors, oral medication, or laboratory data, including the estimated glomerular filtration rate (eGFR), brain natriuretic peptide, and left ventricular ejection fraction. ASV therapy was associated with a reduced incidence of arrhythmia after adjusting for demographic and cardiovascular disease risk factors (odds ratio, 0.27; 95% confidence interval, 0.11 to 0.63; p<0.01; compared to the Non-ASV group). In addition, at the 1-year follow-up, an improvement (increase) in the eGFR was found in the ASV group but not in the Non-ASV group. Conclusion ASV therapy was able to prevent arrhythmias, including PAF and VT, with short-term improvements in the renal function in patients with HF due to IHD.

Sex differences in left ventricular afterload and diastolic function are independent from the aortic size.

BACKGROUND: Women have a greater risk of heart failure with preserved ejection fraction (HFPEF) than men do, yet the basis for this disparity remains unclear. Greater arterial stiffness and afterload causes left ventricular (LV) diastolic dysfunction, a central mechanism of HFPEF. Because of smaller body habitus, previous reports have used body surface area as a surrogate of the size of the aorta. We performed a comprehensive hemodynamic evaluation of elderly patients with preserved EF and evaluated sex differences in the associations between LV function and afterload, before and after adjusting for the aortic sizes. METHODS AND RESULTS: Four hundred and forty-three patients (mean age: 73 years, 169 women) who underwent clinically indicated echocardiography and computed tomography (CT) were identified. Linear regression analyses were performed to assess the independent contributions of sex to and its interaction with LV function before and after adjusting for CT-derived aortic length and volume. Although blood pressures were similar between the sexes, women had greater arterial elastance, lower arterial compliance, and greater LV ejection fraction (all p<0.001). Sex differences were detected in the associations between LV afterload and relaxation (mitral e') as well as in the left atrial (LA) emptying fraction, but not in LA size. These differences remained significant after adjusting for the aortic length and volume. Sensitivity analyses in an age-matched subgroup (n = 324; 162 of each sex) confirmed the robustness of these sex disparities in LV diastolic function and afterload. CONCLUSION: Women had worse LV relaxation than men did against the same degree of afterload, before and even after adjusting for the aortic sizes.

Dobutamine stress 99mTc-tetrofosmin quantitative gated SPECT predicts improvement of cardiac function after carvedilol treatment in patients with dilated cardiomyopathy.

UNLABELLED: We evaluated whether dobutamine stress (99m)Tc-tetrofosmin quantitative gated SPECT (D-QGS) could predict improvement of cardiac function by carvedilol therapy in patients with dilated cardiomyopathy (DCM). METHODS: The study included 30 patients with idiopathic DCM and a left ventricular ejection fraction (LVEF) of <45%. D-QGS was performed in all patients to measure LVEF at rest and during dobutamine infusion (10 microg/kg/min). LVEF and left ventricular end-diastolic volume (LVEDV) were determined by echocardiography, plasma brain natriuretic peptide (BNP) was measured, and the New York Heart Association (NYHA) functional class was estimated at baseline and after 1 y of combined treatment with an angiotensin-converting enzyme (ACE) inhibitor, diuretic, and the beta-blocker carvedilol. After treatment, the echocardiographic LVEF improved by >5% in 15 patients (group A) but did not improve in the remaining 15 patients (group B). RESULTS: The baseline LVEF, LVEDV, plasma BNP, and NYHA functional class were similar in both groups. However, there was a greater increase of LVEF (Delta LVEF) with dobutamine infusion during D-QGS in group A than that in group B (12.0% +/- 5.8% vs. 2.7% +/- 4.2%, P < 0.0001). When a cutoff value of 6.6% for Delta LVEF was used to predict the improvement of LVEF by carvedilol therapy, the sensitivity was 86.7%, the specificity was 86.7%, and the accuracy was 86.7%. LVEDV, plasma BNP, and NYHA functional class all showed superior improvement in group A compared with group B. CONCLUSION: Delta LVEF measured by D-QGS was significantly larger in patients who responded to carvedilol than that in nonresponders. These findings indicate that D-QGS can be used to predict improvement of cardiac function and heart failure symptoms by carvedilol therapy in patients with idiopathic DCM.

Left atrial strain provides incremental value for embolism risk stratification over CHA2DS2-VASc score and indicates prognostic impact in patients with atrial fibrillation.

BACKGROUND: The aim of this study was to investigate whether left atrial (LA) strain has incremental value over the CHA2DS2-VASc score for stratifying the risk for embolism in patients with atrial fibrillation (AF) and whether LA strain predicts poststroke mortality. METHODS: Consecutive patients with paroxysmal or persistent AF with acute embolism (82 patients) or without (204 controls) were prospectively enrolled. Global peak LA longitudinal strain during ventricular systole (LAS) was assessed during AF rhythm. Global LAS was compared between the groups in the first cross-sectional study. Then, the 82 patients with acute embolism were prospectively followed during the second prospective cohort study. RESULTS: Global LAS was lower in patients with acute embolism than in controls (P < .001). Global LAS < 15.4% differentiated patients with acute embolism from controls, with an area under the curve of 0.83 (P < .0001). In multivariate analysis, global LAS was independently associated with acute embolism (odds ratio, 0.74; 95% confidence interval, 0.67-0.82; P < .001) and had an incremental value over the CHA2DS2-VASc score (P < .0001). Furthermore, 26 patients with acute embolisms died during a median follow-up period of 425 days. Global LAS independently predicted mortality after embolism. CONCLUSIONS: In this observational study, LA strain provided incremental diagnostic information over that provided by the CHA2DS2-VASc score, suggesting that LA strain analysis could improve the current risk stratification of embolism in patients with AF. LA strain can also predict poststroke mortality.

Novel KCNQ1 splicing mutation in patients with forme fruste LQT1 aggravated by hypokalemia.

BACKGROUND: Several KCNQ1 splicing mutations have been identified in patients with type-1 long QT syndrome (LQT1). It was suggested that the clinical severity may differ according to the aberrant splicing products. There may be precipitating factors that cause cardiac events in those with a mild clinical phenotype (forme fruste LQT1). METHODS AND RESULTS: We analyzed the KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes in 31 consecutive LQTS patients. A novel KCNQ1 1251+1G>A (IVS9+1G>A) mutation was identified in three probands and their two relatives. The QT interval in all of the five individuals with mutation was not much prolonged in the absence of precipitating factors (mean QTc was 461±30ms.). Two of the five individuals with mutation were symptomatic. One patient (a 38-year-old female) had experienced recurrent episodes of syncope due to ventricular tachyarrhythmias (VTAs) accompanied by QT prolongation (QTc: 750ms) when the serum potassium concentration ([K(+)]) was 2.7mEq/L. After correction of [K(+)], the QTc interval was shortened to 515ms, and the occurrence of VTAs ceased. Another patient (a 22-year-old female) was resuscitated from cardio-pulmonary arrest due to VTAs. Just after resuscitation, the QTc interval was 629ms, and [K(+)] was 2.9mEq/L. After correction of [K(+)], the QTc interval was dramatically shortened to 440ms. In order to identify abnormal splicing products of the responsible mutation, we analyzed the reverse transcription-polymerase chain reaction products from peripheral bloods of the mutation carrier, and identified exon 9-skipping (Δ9) and cryptic sequential exons 8 and 9-skipping (Δ8-9) products, as well as a no exon-skipping product. CONCLUSIONS: We identified a novel KCNQ splicing mutation 1251+1G>A in forme fruste LQT1, which induces cryptic splicing. Two of the five individuals with mutation experienced VTAs in the setting of hypokalemia, emphasizing the need to increase awareness of the significance of hypokalemia in this subgroup of LQT1 patients.

Incremental diagnostic value of la strain with leg lifts in heart failure with preserved ejection fraction.

OBJECTIVES: The purposes of this study were to examine left atrial (LA) functional reserve in patients with heart failure (HF) with preserved ejection fraction (HFpEF) and to determine whether LA strain has an incremental diagnostic value over clinical and conventional echocardiographic parameters. BACKGROUND: Patients with HFpEF have multiple cardiovascular reserve abnormalities. Although the LA is dysfunctional in HFpEF, the diagnostic value of LA strain remains unknown. METHODS: The LA at rest and during passive leg lifts was echocardiographically assessed in 40 patients with HFpEF and in 46 patients with hypertension without HF (HT controls). Global peak atrial longitudinal strain during ventricular systole (global LAS) and booster strain during atrial contraction (global LAB) were assessed using speckle tracking. RESULTS: Patients with HFpEF had an enlarged LA and reduced LA emptying fraction compared with HT controls at rest, while LA stroke volume (SV) was similar between the groups. During leg lifts, increases in LA reservoir and contractile function (i.e., global LAS and LAB) were blunted in HFpEF patients compared with HT controls, resulting in impaired LASV responses. Global LAS and LAB during leg lifts accurately differentiated HFpEF from HT controls (areas under the curve: 0.95 and 0.92, respectively). Resting global LAS had a significant incremental diagnostic value over clinical (age and sex) and conventional echocardiographic parameters (E/E' ratio, left ventricular mass index, and maximum LA volume index) (global chi-square: 49.6 vs. 30.8; p < 0.0001). The diagnostic value was further improved by adding global LAS during leg lifts (global chi-square: 72.2 vs. 49.6; p < 0.0001). CONCLUSIONS: An enlarged LA compensates for LA dysfunction and maintains LASV at rest in patients with HFpEF. However, depressed LA reserve affects LA performance during leg lifts. Evaluation of LA function, including LA strain using leg lifts, might provide incremental diagnostic value for HFpEF.

Combination therapy for adult coronary artery aneurysm with off-pump coronary artery bypass grafting and vein graft-coated stent.

We report on a 51-year-old Japanese female with bilateral coronary artery aneurysms. Severe calcified aneurysms were detected in the proximal right coronary artery (RCA) and left anterior descending branch (LAD). The RCA was totally occluded and supplied by the blood flow via septal branches of the LAD. A two-stage management plan, including an off-pump coronary artery bypass grafting for the RCA with a right gastroepiploic artery and catheter angioplasty with an autologous vein graft-coated stent for the LAD, was successfully completed. Prophylactic treatments for coronary artery aneurysm are still controversial, therefore, minimal invasive procedures should be favored to prevent acute cardiac shock or sudden death related to aneurysmal obstruction.