KCNQ1 suppression-replacement gene therapy in transgenic rabbits with type 1 long QT syndrome.

BACKGROUND AND AIMS: Type 1 long QT syndrome (LQT1) is caused by pathogenic variants in the KCNQ1-encoded Kv7.1 potassium channels, which pathologically prolong ventricular action potential duration (APD). Herein, the pathologic phenotype in transgenic LQT1 rabbits is rescued using a novel KCNQ1 suppression-replacement (SupRep) gene therapy. METHODS: KCNQ1-SupRep gene therapy was developed by combining into a single construct a KCNQ1 shRNA (suppression) and an shRNA-immune KCNQ1 cDNA (replacement), packaged into adeno-associated virus serotype 9, and delivered in vivo via an intra-aortic root injection (1E10 vg/kg). To ascertain the efficacy of SupRep, 12-lead electrocardiograms were assessed in adult LQT1 and wild-type (WT) rabbits and patch-clamp experiments were performed on isolated ventricular cardiomyocytes. RESULTS: KCNQ1-SupRep treatment of LQT1 rabbits resulted in significant shortening of the pathologically prolonged QT index (QTi) towards WT levels. Ventricular cardiomyocytes isolated from treated LQT1 rabbits demonstrated pronounced shortening of APD compared to LQT1 controls, leading to levels similar to WT (LQT1-UT vs. LQT1-SupRep, P < .0001, LQT1-SupRep vs. WT, P = ns). Under ß-adrenergic stimulation with isoproterenol, SupRep-treated rabbits demonstrated a WT-like physiological QTi and APD90 behaviour. CONCLUSIONS: This study provides the first animal-model, proof-of-concept gene therapy for correction of LQT1. In LQT1 rabbits, treatment with KCNQ1-SupRep gene therapy normalized the clinical QTi and cellular APD90 to near WT levels both at baseline and after isoproterenol. If similar QT/APD correction can be achieved with intravenous administration of KCNQ1-SupRep gene therapy in LQT1 rabbits, these encouraging data should compel continued development of this gene therapy for patients with LQT1.

Beneficial normalization of cardiac repolarization by carnitine in transgenic SQT1 rabbit models.

AIMS: Short-QT-syndrome type 1 (SQT1) is a genetic channelopathy caused by gain-of-function variants in HERG underlying the rapid delayed-rectifier K+ current (IKr), leading to QT-shortening, ventricular arrhythmias, and sudden cardiac death. Data on efficient pharmaco-therapy for SQT1 are scarce. In patients with primary carnitine-deficiency, acquired-SQTS has been observed and rescued by carnitine-supplementation. Here, we assessed whether carnitine exerts direct beneficial (prolonging) effects on cardiac repolarization in genetic SQTS. METHODS AND RESULTS: Adult wild-type (WT) and transgenic SQT1 rabbits (HERG-N588K, gain of IKr) were used. In vivo ECGs, ex vivo monophasic action potentials (APs) in Langendorff-perfused hearts, and cellular ventricular APs and ion currents were assessed at baseline and during L-Carnitine/C16-Carnitine-perfusion. 2D computer simulations were performed to assess reentry-based VT-inducibility.L-Carnitine/C16-Carnitine prolonged QT intervals in WT and SQT1, leading to QT-normalization in SQT1. Similarly, monophasic and cellular AP duration (APD) was prolonged by L-Carnitine/C16-Carnitine in WT and SQT1. As underlying mechanisms, we identified acute effects on the main repolarizing ion currents: IKr-steady, which is pathologically increased in SQT1, was reduced by L-Carnitine/C16-Carnitine and deactivation kinetics were accelerated. Moreover, L-Carnitine/C16-Carnitine decreased IKs-steady and IK1. In silico modelling identified IKr-changes as main factor for L-Carnitine/C16-Carnitine-induced APD-prolongation. 2D-simulations revealed increased sustained reentry-based arrhythmia formation in SQT1 compared to WT, which was decreased to the WT-level when adding carnitine-induced ion current changes. CONCLUSION: L-Carnitine/C16-Carnitine prolong/normalize QT and whole heart/cellular APD in SQT1 rabbits. These beneficial effects are mediated by acute effects on IKr. L-Carnitine may serve as potential future QT-normalizing, anti-arrhythmic therapy in SQT1.

Transcatheter aortic valve replacement in Germany with need for a surgical bailout.

BACKGROUND: In transcatheter aortic valve replacement (TAVR), complications may force the need for a surgical bailout, but knowledge is rare about outcomes in Germany. METHODS: Using national health records, we investigated all TAVR in German hospitals between 2007 and 2020, focusing on 2018-2020. We extracted data on those interventions with need for a surgical bailout. RESULTS: A total of 159,643 TAVR were analyzed, with an overall rate of surgical bailout of 2.30 %, an overall in-hospital mortality of 3.85 %, and in-hospital mortality in case of bailout of 16.51 %. The number of all annual TAVR procedures increased substantially (202 to 22,972), with the rate of surgical bailout declining from 27.23 to 0.61 % and overall mortality from 11.39 to 2.29 %. However, in-hospital mortality after bailout was still high (28.37 % in 2020). The standardized rates of overall mortality and surgical bailout between 2018 and 2020 were significantly lower for balloon-expandable and self-expanding transfemoral TAVR than for transapical TAVR after risk adjustment [transapical/transfemoral balloon-expandable/transfemoral self-expanding TAVR: in-hospital mortality: 5.66 % (95 % CI 4.81 %; 6.52 %)/2.30 % (2.03 %; 2.57 %)/2.32 % (2.07 %; 2.57 %); surgical bailout: 2.33 % (1.68 %; 2.97 %)/0.79 % (0.60 %; 0.98 %)/0.42 % (0.31 %; 0.53 %)]. Coronary artery disease [risk-adjusted OR = 1.50 (1.21; 1.85), p < 0.001] and atrial fibrillation [OR = 1.29 (1.07; 1.57), p = 0.009] were found to be the main risk factors for bailout. CONCLUSIONS: Rates of TAVR with need for a surgical bailout and overall in-hospital mortality have declined noticeably over the years in Germany. However, the outcomes are still unfavorable after surgical bailout, as in-hospital mortality is continuously high. We present risk factors for surgical bailout to improve preparation of subsequent measures. It must be a major goal to further reduce the rate of surgical bailouts in the future.