Citations

Background: Long QT syndrome (LQTS) is a genetic heart disease affecting about 1 in 2000 persons. Around 40% of patients with LQTS can have a nondiagnostic, normal QTc at rest. The treadmill exercise stress test (TEST) can help unmask patients with concealed LQTS with a characteristic maladaptive, paradoxical increase in QTc ( 460 ms) during the recovery phase. In fact, the recovery phase QTc value has been added to the latest diagnostic score for LQTS. Objective: To characterize the TEST-derived QTc profile of untreated patients with LQTS and determine its diagnostic and prognostic utility. Methods: Retrospective analysis was performed on TEST data derived from 249 patients with LQTS (129 LQT1, 64 LQT2 and 56 LQT3) untreated at the time of their TEST compared with 236 controls. The Bazett’s corrected QTc was calculated at rest (sitting, supine, and standing), during exercise at 1 min, 3 mins, and peak exercise, and during recovery phase at 1, 3 and 5 mins. Results: The mean resting QTc was significantly higher in LQTS patients (457 ± 30 ms) compared to controls (420 ± 24 ms; p<0.0001) as well as at every stage during the TEST (p<0.001). For LQT1 patients, highest QTc was observed at peak exercise (mean 496 ± 38 ms) and during the third minute of recovery phase (mean 500 ± 40 ms). In contrast, LQT2 patients showed the lowest QTc (mean 452 ± 48 ms) during peak exercise but the greatest QTc latency (QTc at 5 min - QTc at 1 min recovery; mean QTc latency 33 ± 77 ms; p=0.005) compared to controls. For LQT3, the mean QTc was greatest at rest compared to controls (p<0.001), and there was no difference during exercise and recovery phases. Among 162 LQT1 and LQT2 patients that presented with concealed LQTS, 119 (73%) showed a maladaptive QT response. ROC analysis showed that in patients with LQT1, a maladaptive QTc > 523 ms at 3 min of recovery was highly predictive of breakthrough cardiac events (AUC 0.84; sensitivity 100%, specificity 72%); no such association was identified for LQT2 or 3. Conclusions: This comprehensive characterization of the QTc response before, during, and after a TEST in the largest untreated cohort of patients with LQTS provides important genotype-specific characteristics and can be used as a predictor for potential LQT1-triggered cardiac events after diagnosis and treatment.

Introduction: Hypertrophic cardiomyopathy (HCM) is characterized by left ventricular hypertrophy. Approximately 40-50% of HCM is caused by pathogenic variants in genes encoding proteins of the cardiac sarcomere. Patients with sarcomeric HCM have earlier expression and more severe disease progression. Herein, we evaluated the proteomic differences between patients with sarcomeric HCM and genotype negative HCM. Methods: Mass-spectrometry was performed on cardiac tissue from genotyped patients with HCM obtained after surgical myectomy, followed by differential proteomics (log2fc ≥

Introduction: Pathogenic loss-of-function variants in the RBM20 -encoded RNA-binding motif 20 splicing regulator cause a severe form of arrhythmogenic dilated cardiomyopathy (DCM). Erroneous splicing of TTN -encoded titin contributes to the pathogenesis of RBM20 -mediated disease. However, studies exploring the clinical course of RBM20 -mediated arrhythmogenic DCM alone or in comparison to TTN -mediated DCM, the most common familial cause of DCM, are lacking. Methods: The Mayo Clinic Genetic Arrhythmogenic Cardiomyopathy Registry (n=391) was used to identify all patients with a pathogenic/likely pathogenic (P/LP) variant in either RBM20 or TTN . For the purposes of this study, a ventricular arrhythmia (VA) event was defined as sudden cardiac arrest, sustained ventricular arrhythmia, or an appropriate ICD shock and an advanced heart failure (AHF) event was defined as ventricular assist device implantation or heart transplantation. Results: Overall, 40 patients with a P/LP variant in RBM20 (50% female) and 70 patients with a P/LP variant in TTN (43% female) were identified. The prevalence of a cardiac phenotype in patients with RBM20- and TTN -mediated disease was 88% and 83%, respectively. RBM20 patients were more likely to have a family history of sudden cardiac arrest (78% vs 34%; p < 0.0001) and cardiomyopathy (90% vs 61%; p=0.001). No difference in rate of ICD implantation (35% versus 33%) was observed. Interestingly, the prevalence of AHF events (10% vs 6%; p=0.5) and VA events (28% vs 24%; p=0.7) was similar between RBM20 - and TTN -positive patients. However, RBM20 patients were younger than TTN patients at the time of their event (37 ± 18 years vs 50 ± 17; p=0.0004). Time-to-event analysis showed RBM20 patients had an earlier time to AHF event (p=0.05) and time to VA event (p=0.03) than TTN patients. The mean age for AHF events was 25 years for RBM20 patients (N=4) and 47 years for TTN patients (N=4). The mean age for VA events was 29 years for RBM20 patients (N=10) and 42 years for TTN patients (N=14). Conclusions: RBM20 -mediated arrhythmogenic DCM represents a highly penetrant genetic heart disease with potentially life-threatening VAs and end stage heart failure manifestations occurring at a significantly younger age in comparison to TTN -mediated DCM.

Introduction: Myocardial inflammation likely contributes to the pathogenesis of arrhythmogenic cardiomyopathy (ACM), a clinically and genetically heterogenous disorder characterized by ventricular dysfunction and potentially life-threatening ventricular arrhythmias. Due to phenotypic overlap, some patients with genetic ACM may have been evaluated for an underlying inflammatory cardiomyopathy, namely cardiac sarcoidosis. However, the cardiac fludeoxyglucose (FDG) positron emission tomography (PET) findings in ACM patients have not been assessed systematically. Methods: All genotype-positive patients in the Mayo Clinic ACM registry who received a cardiac FDG PET were included in this study. The cardiac FDG PET scan consisted of a resting myocardial perfusion scan with N13-ammonia as well as a F18-FDG scan after a high-fat diet to suppress physiologic FDG uptake. Pertinent demographic, genetic, imaging, and outcome data were extracted from the medical record. Results: Collectively, 12 (75% female) genotype-positive ACM patients received a cardiac PET FDG scan as part of their clinical evaluation (median age at scan 45.3 years [IQR 38.9-62.1]). Amongst these patients, pathogenic/likely pathogenic variants were detected in LMNA (n=7), DSP (n=3), FLNC (n=1), and PLN (n=1). Of note, 6/12 (50%) had abnormal myocardial FDG uptake, including diffuse (entire myocardium) uptake in 2/6 (33%), focal (1-2 segments) uptake in 2/6 (33%) and patchy (3+ segments) in 2/6 (33%). Median myocardial standardized uptake value ratio was 2.1 (IQR 1.5-2.6). Interestingly, LMNA -positive patients accounted for 3 out of 6 (50%) positive studies (diffuse uptake in 2 and focal uptake in 1). Conclusion: Myocardial FDG uptake is common in genetic ACM patients undergoing cardiac FDG PET. This finding further supports the role of myocardial inflammation in genetic ACM and demonstrates the ability of cardiac FDG PET to readily detect this phenomenon. Further investigation is needed to determine (i) the role of cardiac FDG PET in the evaluation of genetic ACM, (ii) if FDG uptake in genetic ACM has prognostic value and (iii) whether the attenuation of myocardial inflammation with immunosuppressive agents can impact the clinical course of inflammatory genetic ACMs.

Introduction: Multifocal ectopic Purkinje-related premature contractions (MEPPC), the most recent addition to the spectrum of SCN5A -mediated cardiac channelopathies, is characterized by frequent premature ventricular complexes (PVCs) originating from the Purkinje system, atrial arrhythmias, and a predilection for PVC-mediated dilated cardiomyopathy. Hypothesis: To investigate the electrophysiology phenotype of MEPPC in a novel, patient-specific, re-engineered cardiomyocyte model. Methods: Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from a 27-year-old male with a history of frequent, multifocal PVCs and atrial tachycardia, positive for a putative MEPPC-causative SCN5A variant (p.Q419P). A CRISPR-Cas9 Q419P variant-corrected isogenic control (IC) was created to establish the normalized electrophysiology recordings for that MEPPC model. The standard whole-cell patch clamp technique was used to measure Q419P-SCN5A- and IC-derived NaV1.5 sodium currents using voltage clamp configuration. In addition, action potential duration (APD) of the iPSC-CMs were measured using FluoVolt optical voltage-sensing dye. Results: Analysis of the current-voltage relationship revealed that neither peak sodium current densities nor late inward sodium current were impacted by Q419P-SCN5A. However, Q419P-SCN5A significantly right-shifted the V 1/2 in inactivation by 8.3 mV from -81.1±1.7 mV (IC, n=5) to -72.8±0.2 mV (Q419P-SCN5A, n=6, p<0.05 vs. IC) and left-shifted the V 1/2 in activation by -4.1 mV from -39.5±0.3 mV (IC, n=5) to -43.6±0.9 mV (Q419P-SCN5A, n=6, p<0.05 vs. IC) leading to a larger hyperpolarized window current. Optical APD90 measurement revealed no difference between the Q419P-containing (476 ± 23 ms) and the IC (474 ± 46 ms, p=0.867) cardiomyocytes. Conclusions: This is the first in-vitro disease model of MEPPC using patient-specific, re-engineered heart cells. Consistent with the findings in the non-cardiac HEK cell system, this MEPPC-causative variant contributes to increased window current in cardiomyocytes without affecting the cardiac APD. This novel cardiac cell model for MEPPC may facilitate new insights into the pathobiology of MEPPC and enable the testing of novel therapies for it.

Introduction: Cardiac sarcoidosis (CS) is a non-ischemic disease which can present with right ventricular (RV) dysfunction, but there is a paucity of research describing RV function and natural history in CS. Methods: We queried a registry of 512 CS patients for those with baseline and follow-up echocardiography (TTE). Demographics, medications, and baseline/follow-up TTE data were collected. RV-pulmonary arterial (RV-PA) coupling was approximated by ratio of tricuspid annular plane systolic excursion to estimated pulmonary artery systolic pressure (TAPSE:ePASP). Results: Our query yielded 343 CS patients with mean age 56y (σ=12y), who were predominantly male (67%) and white (90%) with a median follow-up 4y (interquartile range 4.1y). Most had pulmonary sarcoidosis (68%). Baseline TTE data showed left ventricular ejection fraction 48% (σ=14), abnormal RV function with RV systolic pressure (ePASP) 34 mmHg (σ=11), TAPSE 21mm (σ=5), RV S′ 0.14 m/s (σ=0.07), and RV-PA uncoupling (TAPSE:ePASP 0.69 mm/mm Hg, σ=0.25). Baseline RV function parameters did not differ by pulmonary involvement of sarcoidosis. 92% received immunosuppression and 65% received neurohormonal blockade. In long-term follow-up, the overall cohort demonstrated a trend towards worsening of both RV S’ and RV-PA coupling (P=.02 and P=.003 for linear trend, respectively) but stable ePASP (P=.11). Trends in both non-invasive ePASP and RV-PA coupling were similar in patients with and without pulmonary involvement (P=.48 and P=.79, respectively). Conclusions: In our large CS cohort with extensive follow-up, metrics of RV function and RV-PA coupling are often abnormal at CS diagnosis. Echocardiographic measures of PASP tend to remain stable but markers of RV dysfunction, including RV-PA coupling, tend to worsen throughout the disease course irrespective of pulmonary sarcoidosis. More granular phenotyping of pulmonary hypertension in CS is required to better understand this relationship.

Background: Highly caffeinated energy drinks (HCEDs) can trigger life-threatening cardiac arrhythmias in individuals with and without an underlying genetic predisposition. Though the mechanism(s) responsible for these events remain unclear, it has been postulated that high caffeine may alter heart rate, blood pressure, cardiac contractility, and cardiac repolarization in a manner that is pro-arrhythmic. Objective: To describe our experience regarding sudden cardiac arrest (SCA) events occurring in proximity to HCED consumption in patients with underling genetic heart diseases. Methods: All SCA survivors referred to the Mayo Clinic Windland Smith Rice Genetic Heart Rhythm Clinic for clinical and/or molecular evaluation were reviewed to identify those with a history of HCED consumption prior to their event. Patient demographics, clinical characteristics, documented HCED consumption, and temporal relationship of HCED consumption to SCA were extracted from the electronic medical record. Results: Among 144 SCA survivors with a structurally normal heart, 8 (6 females; mean age at event 28 ± 8 years) experienced an unexplained SCA associated temporally with HCED consumption. Of these, 5 (63%) had either long QT syndrome (n=3) or catecholaminergic polymorphic ventricular tachycardia (n=2). The remaining 3 were diagnosed with unexplained SCA/idiopathic ventricular fibrillation after a comprehensive evaluation. Three patients (37%) were habitual HCED consumers while 5 (63%) imbibed for the first time with consumption ranging from several hours to a few minutes before the SCA. Seven patients (88%) required a rescue shock (average 2 ± 2 shocks/patient) while 1 was manually resuscitated. Upon follow-up, 6 (75%) were dismissed with an implantable cardioverter defibrillator, 1 (13%) on pharmacologic therapy, and 1 (13%) underwent denervation surgery. All SCA survivors have quit drinking HCEDs and have been event-free since. Conclusion: Overall, 8/144 (5.6%) of SCA survivors evaluated in our program experienced a SCA in proximity to consuming a HCED. Although larger cohort studies are needed to elucidate the precise mechanism for HCED-triggered/associated SCA and quantify its precise pro-arrhythmic risk, it seems prudent to sound an early warning.

Background: The estimated prevalence of attention-deficit/hyperactivity disorder (ADHD) globally is about 5%. For patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), ADHD-directed stimulant therapy is relatively contraindicated. However, previous studies have shown that use of these treatments is safe for patients with long QT syndrome, a similar genetic heart disease. Whether this is the same for patients with CPVT remains unknown. Objective: To evaluate ADHD-directed treatment, outcome, and frequency of CPVT-triggered events in patients with CPVT and concomitant ADHD. Methods: A retrospective electronic medical record review of 216 patients with CPVT evaluated in Mayo Clinic’s Windland Smith Rice Genetic Heart Rhythm Clinic was performed to determine the prevalence of concomitant ADHD and the incidence of CPVT-triggered events in these patients. Results: Overall, 14 patients (6%) were diagnosed with CPVT and concomitant ADHD (6 female, average age 19 ± 3 years). At the time of first evaluation, ADHD-directed stimulant therapy was stopped or advised against in 8/14 patients (57%). It was (re)started in 11 patients (79%) following comprehensive evaluation and treatment initiation for CPVT with pharmacologic therapy in 14/14 patients (100%), denervation surgery in 12 (86%), and an implantable cardioverter defibrillator in 4 (29%). Prior to Mayo Clinic evaluation, 10 patients (71%) treated for CPVT had a breakthrough cardiac event, without being on stimulant therapy, while 4 patients (29%) had an event while being treated for both CPVT and ADHD for an average time on stimulant therapy of 6 ± 6 years. Following CPVT treatment optimization and ADHD stimulant (re)initiation, patients have remained event-free for a total of 82 patient years (mean follow-up 6 ± 5 years). Conclusion: Among patients with CPVT, the prevalence of ADHD was similar to that in the general population, which can be treated safely and effectively with stimulant therapy. Although the rate of adverse events was low in stimulant-treated patients, physicians should weigh the potential effects of suboptimal treatment of ADHD with the theoretical proarrhythmic risk from stimulant medications on a case-by-case basis.

Background: Long QT syndrome (LQTS) stems from cardiac action potential duration (APD) prolonging pathogenic variants in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3). Sodium/glucose co-transporter 2 inhibitor (SGLT2i), a class of drugs used to treat type II diabetes and all forms of heart failure, reduces cardiac late sodium channel current. Objective: To test the ability of three commercially available SGLT2i to reduce APD in patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) models of LQT1, LQT2, and LQT3. Method: Patient-specific iPSC-CMs and a CRISPR/Cas9 gene-edited variant corrected, isogenic control (IC) iPSC-CMs were generated. The variant-corrected IC was used to determine the curative APD in order to establish the degree of APD attenuation. The SCN5A-P1332L (LQT3) and IC iPSC-CMs were tested with 10 μM of either canagliflozin (CANA), dapagliflozin (DAPA), or empagliflozin (EMPA). An ATXII (5μM)-induced APD prolongation iPSC-CM model, mimicking drug-induced LQT3, was also treated. The APD was measured 30 minutes, 1 hour, and 2 hours after treatment using local extracellular action potential recordings on multielectrode array. The efficacy of these SGLT2i were also tested in KCNQ1-V254M (LQT1) and KCNH2-G604S (LQT2) iPSC-CMs. Results: The APD90 was prolonged in SCN5A-P1332L iPSC-CMs compared to its IC (469 ± 4 ms vs 305 ± 2 ms, p<0.0001). While 10 μM of SGLT2i had no APD shortening effect on the KCNQ1-V254M or KCNH2-G604S iPSC-CMs, all three SGLT2i compounds shortened the APD90 of the SCN5A-P1332L iPSC-CMs after 1 hour of treatment from 463±5 ms to 432±6 ms (EMPA, 18.8% attenuation, p=0.0002), 459±8 ms to 430±5 ms (CANA, 17.5%, p=0.004), and 453±6 ms to 434±4 ms (DAPA, 11.4%, p=0.01). Additionally, IC iPSC-CMs treated with 5 μM of ATXII induced significant APD prolongation from 318±9 ms to 379±12 ms (p=0.0003) after 30 min incubation. However, co-incubation of ATXII and SGLT2i abolished the APD prolonging effect of ATXII. Conclusions: Therapeutically inhibiting SGLT2 effectively shortens the cardiomyocyte APD in human heart cell models of the LQT3, but not LQT1 or LQT2. This pre-clinical data compels further assessment of SGLT2i as a novel therapy for patients with congenital LQT3.

Introduction: Gain-of-function mutations in SCN5A- encoded cardiac sodium channel (Na V 1.5) cause type 3 long QT syndrome (LQT3). Patients with SCN5A variants localizing to the local anesthetic binding domain might not be sensitive to lidocaine or mexiletine treatment. Hypothesis: Phenytoin, a sodium channel blocker used to treat epilepsy, may be a novel LQT3-directed therapy for a variant involving a critical residue of the Nav1.5’s local anesthetic binding domain. Methods: SCN5A-F1760C was identified in a now deceased infant with severe LQT3 (QTc of 680-1200 ms) who was refractory to left cardiac sympathetic denervation and pharmacological treatments with either lidocaine or mexiletine. SCN5A-F1760C was engineered by site directed mutagenesis and expressed in TSA201 cells. Patient-specific pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from the SCN5A-F1760C-positive infant and gene-edited/variant-corrected isogenic control (IC) iPSC-CMs were generated. Na V 1.5 currents were recorded in TSA201 cells transfected with SCN5A-WT/ F1760C and action potentials (APs) from iPSC-CMs were recorded before and after treatment with 5μM Phenytoin using the whole cell patch-clamp technique. Results: SCN5A-F1760C did not change the NaV1.5 current density. However, the V1/2 of inactivation was right-shifted significantly by +14.1 mV from -86.3±0.9 mV (WT) to -72.2±0.7 mV (F1760C, p<0.0001) resulting in a marked increase in window current. F1760C increased sodium late current 2-fold from 0.18±0.04% in WT to 0.49±0.07% in F1760C (p=0.0005). Baseline APD to 90% repolarization (APD90) was prolonged significantly in F1760C-derived iPSC-CMs (641±40 ms) compared to IC iPSC-CMs (412±22 ms, p<0.0001). Treatment with 5μM phenytoin normalized the APD90 in F1760C-derived iPSC-CMs to 423+34 ms (p<0.0001), values approximating the ‘gene/variant-edited’ cure. Conclusions: Na V 1.5 gain-of-function caused by a novel SCN5A-F1760C variant results in marked APD90 prolongation which were rescued by phenytoin indicating the antiepileptic drug, phenytoin, may be a mutation-specific, LQT3-directed therapy for those LQT3-causative variants that disrupt the local anesthetic/lidocaine-binding domain.