Proceed with caution: Standard protocol exercise stress tests fail to replicate the diagnostic utility of supine-stand tests for long QT syndrome

BACKGROUND

Long QT syndrome (LQTS) is a sudden death predisposing condition characterized by ECG-derived prolongation of the QT interval. Previous studies have demonstrated that the supine-stand test may aid in the diagnosis of LQTS as patients fail to shorten their QT interval in response to standing up. The aim of this study was to evaluate the diagnostic accuracy of ECG data derived from standard protocol, clinically performed treadmill exercise stress tests (TESTs) in their ability to mimic the formal supine-stand test.

METHODS

We performed a retrospective review of 478 TESTs from patients evaluated for LQTS. Patients referred for evaluation of LQTS but who were dismissed as normal served as controls. Heart rate & QT values were obtained from standard protocol TESTs.

RESULTS

Overall, 243 patients with LQTS (125 LQT1, 63 LQT2, 55 LQT3; 146 [60%] female, mean age at TEST 30 ± 17 years) and 235 controls (142 [60%] female, mean age 24 ± 15 years) were included. The paired ΔQTc (QTcStand -QTcSupine ) was similar between LQTS (-5 ± 26) and controls (-2 ± 25; p = .2). During position change, the QT interval shortened by ≥20 ms in 33% of LQTS patients, remained unchanged in 62%, and increased in 5% of LQTS patients which was similar to controls (shortened in 40%, unchanged in 54%, and increased in 6% of controls; p = .2). Receiver-operator curve analysis to test the diagnostic ability of supine-stand ΔQT performed poorly in differentiating LQTS from controls with an of AUC 0.52 (p = .4).

CONCLUSION

TESTs should be used with caution when trying to interpret supine-stand changes for diagnosis of LQTS.

A Multi-Omics Atlas of Sex-Specific Differences in Obstructive Hypertrophic Cardiomyopathy

Background

Hypertrophic cardiomyopathy (HCM) is a common genetic heart disease. Women with HCM tend to have a later onset but more severe disease course. However, the underlying pathobiological mechanisms for these differences remain unknown.

Methods

Myectomy samples from 97 patients (53 males/44 females) with symptomatic obstructive HCM and 23 control cardiac tissues were included in this study. RNA-sequencing was performed on all samples. Mass spectrometry-based proteomics and phosphoproteomics was performed on a representative subset of samples.

Results

The transcriptome, proteome, and phosphoproteome was similar between sexes and did not separate on PCA plotting. Overall, there were 482 differentially expressed genes (DEGs) between control females and control males while there were only 53 DEGs between HCM females and HCM males. There were 1963 DEGs between HCM females and control females compared to 1064 DEGs between HCM males and control males. Additionally, there was increased transcriptional downregulation of hypertrophy pathways in HCM females and in HCM males. HCM females had 119 differentially expressed proteins compared to control females while HCM males only had 27 compared to control males. Finally, the phosphoproteome showed females had 341 differentially phosphorylated proteins (DPPs) compared to controls while males only had 184. Interestingly, there was hypophosphorylation and inactivation of hypertrophy pathways in females but hyperphosphorylation and activation in males.

Conclusion

There are subtle, but biologically relevant differences in the multi-omics profile of HCM. This study provides the most comprehensive atlas of sex-specific differences in the transcriptome, proteome, and phosphoproteome present at the time of surgical myectomy for obstructive HCM.

Prognostic Value of Multiplexed Assays of Variant Effect and Automated Patch-clamping for KCNH2-LQTS Risk Stratification

Background

Long QT syndrome (LQTS) is a lethal arrhythmia condition, frequently caused by rare loss-of-function variants in the cardiac potassium channel encoded by KCNH2. Variant-based risk stratification is complicated by heterogenous clinical data, incomplete penetrance, and low-throughput functional data.

Objective

To test the utility of variant-specific features, including high-throughput functional data, to predict cardiac events among KCNH2 variant heterozygotes.

Methods

We quantified cell-surface trafficking of 18,323 variants in KCNH2 and recorded potassium current densities for 506 KCNH2 variants. Next, we deeply phenotyped 1150 KCNH2 missense variant patients, including ECG features, cardiac event history (528 total cardiac events), and mortality. We then assessed variant functional, in silico, structural, and LQTS penetrance data to stratify event-free survival for cardiac events in the study cohort.

Results

Variant-specific current density (HR 0.28 [0.13-0.60]) and estimates of LQTS penetrance incorporating MAVE data (HR 3.16 [1.59-6.27]) were independently predictive of severe cardiac events when controlling for patient-specific features. Risk prediction models incorporating these data significantly improved prediction of 20 year cardiac events (AUC 0.79 [0.75-0.82]) over patient-only covariates (QTc and sex) (AUC 0.73 [0.70-0.77]).

Conclusion

We show that high-throughput functional data, and other variant-specific features, meaningfully contribute to both diagnosis and prognosis of a clinically actionable monogenic disease.

Temporal Association Between Vaping and Risk of Cardiac Events

OBJECTIVE

To describe our early observations with sudden cardiac arrest (SCA) and sudden death (SD) in patients using vape products.

PATIENTS AND METHODS

A retrospective analysis of Mayo Clinic's Windland Smith Rice Genetic Heart Rhythm Clinic and Sudden Death Genomics Laboratory was performed on all SCA survivors and decedents who presented between January 1, 2007, and December 31, 2021, to identify patients/decedents with a history of vaping. Data abstraction included patient demographics, clinical characteristics, and documented use of vape products.

RESULTS

Among 144 SCA survivors and 360 SD victims, there were six individuals (1%; 3 females) with unexplained SCA (n=4) or SD (n=2) that was temporally associated with vaping use with a mean age at sentinel event of 23±5 years. The SCA survivors include a 19-year-old male who was resuscitated from documented ventricular fibrillation 40 minutes after vaping and a 19-year-old male who was resuscitated from ventricular fibrillation a few hours post vaping. The first SD victim was a 19-year-old female with exercise-induced asthma who died in her sleep after vaping that evening. Autopsy results showed eosinophilic infiltrates in the lung tissue and death was attributed to bronchial asthma. The second vaping-associated death involved a 26-year-old male whose autopsy attributed the death to acute respiratory distress syndrome.

CONCLUSION

We have identified six young individuals with a history of vaping who experienced a near fatal episode or a tragic SD. Although larger cohort studies are needed to quantify the actual risk of SD, it seems prudent to sound an early warning about vaping's potential lethality.

Precision therapy in congenital long QT syndrome

Long QT syndrome (LQTS) is a potentially life-threatening, but highly treatable genetic heart disease. LQTS-directed therapies often consist of beta-blockers (BBs), left cardiac sympathetic denervation (LCSD), and/or an implantable cardioverter defibrillator (ICD). However, in clinical practice, many patient-specific and genotype-directed permutations exist. Herein, we aim to review the spectrum of treatment configurations utilized at a single, tertiary center specializing in the care of patients with LQTS to demonstrate optimal LQTS-directed management is not amenable to a "one-size-fits-all" approach but instead benefits from patient- and genotype-tailored strategies.

Flecainide Is Associated With a Lower Incidence of Arrhythmic Events in a Large Cohort of Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

In severely affected patients with catecholaminergic polymorphic ventricular tachycardia, beta-blockers are often insufficiently protective. The purpose of this study was to evaluate whether flecainide is associated with a lower incidence of arrhythmic events (AEs) when added to beta-blockers in a large cohort of patients with catecholaminergic polymorphic ventricular tachycardia.

METHODS

From 2 international registries, this multicenter case cross-over study included patients with a clinical or genetic diagnosis of catecholaminergic polymorphic ventricular tachycardia in whom flecainide was added to beta-blocker therapy. The study period was defined as the period in which background therapy (ie, beta-blocker type [beta1-selective or nonselective]), left cardiac sympathetic denervation, and implantable cardioverter defibrillator treatment status, remained unchanged within individual patients and was divided into pre-flecainide and on-flecainide periods. The primary end point was AEs, defined as sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter defibrillator shock, and arrhythmic syncope. The association of flecainide with AE rates was assessed using a generalized linear mixed model assuming negative binomial distribution and random effects for patients.

RESULTS

A total of 247 patients (123 [50%] females; median age at start of flecainide, 18 years [interquartile range, 14-29]; median flecainide dose, 2.2 mg/kg per day [interquartile range, 1.7-3.1]) were included. At baseline, all patients used a beta-blocker, 70 (28%) had an implantable cardioverter defibrillator, and 21 (9%) had a left cardiac sympathetic denervation. During a median pre-flecainide follow-up of 2.1 years (interquartile range, 0.4-7.2), 41 patients (17%) experienced 58 AEs (annual event rate, 5.6%). During a median on-flecainide follow-up of 2.9 years (interquartile range, 1.0-6.0), 23 patients (9%) experienced 38 AEs (annual event rate, 4.0%). There were significantly fewer AEs after initiation of flecainide (incidence rate ratio, 0.55 [95% CI, 0.38-0.83]; P=0.007). Among patients who were symptomatic before diagnosis or during the pre-flecainide period (n=167), flecainide was associated with significantly fewer AEs (incidence rate ratio, 0.49 [95% CI, 0.31-0.77]; P=0.002). Among patients with ≥1 AE on beta-blocker therapy (n=41), adding flecainide was also associated with significantly fewer AEs (incidence rate ratio, 0.25 [95% CI, 0.14-0.45]; P<0.001).

CONCLUSIONS

For patients with catecholaminergic polymorphic ventricular tachycardia, adding flecainide to beta-blocker therapy was associated with a lower incidence of AEs in the overall cohort, in symptomatic patients, and particularly in patients with breakthrough AEs while on beta-blocker therapy.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry

AIMS

Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms.

METHODS AND RESULTS

The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing.

CONCLUSION

Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

Septal Myectomy Outcomes in Children and Adolescents With Obstructive Hypertrophic Cardiomyopathy

BACKGROUND

Little data exist regarding characteristics and outcomes of pediatric patients undergoing septal myectomy. We evaluated this in a large referral population.

METHODS

Septal myectomy was performed in 199 consecutive patients aged ≤18 years with obstructive hypertrophic cardiomyopathy from January 1, 1976, to June 30, 2021.

RESULTS

Median age was 13 years (interquartile range [IQR], 8-15 years). Left ventricular myectomy approaches included transaortic (163 of 198 [82%]), transapical (16 of 198 [8%]), and combined (19 of 198 [10%]). Right ventricular interventions included myectomy (13 of 199 [7%]) and patch reconstruction of the outflow tract (15 of 199 [8%]). Maximum left ventricular outflow tract gradients decreased after myectomy (prebypass: 50 mm Hg [IQR, 31-73 mm Hg] vs postbypass: 4 mm Hg [IQR, 0-9 mm Hg], P < .001), and this was sustained long-term (5 mm Hg [IQR, 5-10 mm Hg] at 10 years). Iatrogenic aortic and mitral valve injuries occurred in 13 of 199 (7%) and 1 of 199 (1%), respectively; however, all were successfully repaired. Operative mortality was 2 of 199 (1%). The cumulative incidence of redo myectomy was low, at 5.8% at 5 and 8.3% at 10 years. Redo myectomy patients had higher maximum left ventricular outflow tract gradients on echocardiography at predischarge and 1 year and were younger at the index operation (8 years [IQR, 2.5-10 years] vs 13 years [IQR, 9-16 years], P < .001). Overall survival at 10 years was 90%, relative to 47% in a previously reported pediatric nonoperative cohort.

CONCLUSIONS

Pediatric septal myectomy provides safe, effective, and durable relief of ventricular outflow tract obstruction. Iatrogenic valve injury remains a low but nonnegligible risk. Recurrent obstruction requiring redo myectomy is infrequent and can be identified early. Long-term survival in this pediatric septal myectomy cohort appears to fare better than pediatric hypertrophic cardiomyopathy cohorts managed nonoperatively.

Proteomic and phosphoproteomic analyses of myectomy tissue reveals difference between sarcomeric and genotype-negative hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetically heterogenous condition with about half of cases remaining genetically elusive or non-genetic in origin. HCM patients with a positive genetic test (HCMSarc) present earlier and with more severe disease than those with a negative genetic test (HCMNeg). We hypothesized these differences may be due to and/or reflect proteomic and phosphoproteomic differences between the two groups. TMT-labeled mass spectrometry was performed on 15 HCMSarc, 8 HCMNeg, and 7 control samples. There were 243 proteins differentially expressed and 257 proteins differentially phosphorylated between HCMSarc and HCMNeg. About 90% of pathways altered between genotypes were in disease-related pathways and HCMSarc showed enhanced proteomic and phosphoproteomic alterations in these pathways. Thus, we show HCMSarc has enhanced proteomic and phosphoproteomic dysregulation observed which may contribute to the more severe disease phenotype.

Return-to-Play for Elite Athletes With Genetic Heart Diseases Predisposing to Sudden Cardiac Death

BACKGROUND

People diagnosed with genetic heart diseases (GHDs) associated with sudden cardiac death (SCD) have historically been restricted from competitive sports. Recent data documenting return-to-play (RTP) experiences following shared decision making (SDM) suggest that cardiac event rates for athletes with a GHD are lower than previously described, thereby suggesting an opportunity to reconsider this paradigm.

OBJECTIVES

The purpose of this study was to evaluate clinical outcomes among National Collegiate Athletic Association Division I university and professional athletes diagnosed with a GHD.

METHODS

A multicenter retrospective analysis was performed to examine demographics, clinical characteristics, RTP outcomes, and cardiac events among elite athletes with a GHD.

RESULTS

A total of 76 elite (66%, Division I, 34% professional) athletes (age 19.9 ± 5 years, 28% women) diagnosed with a GHD (hypertrophic cardiomyopathy [53%], long QT syndrome, long QT syndrome [26%]) comprise this cohort. Most athletes were asymptomatic (48 of 76, 63%) before diagnosis and had their GHD detected during routine preparticipation cardiovascular screening. Most athletes (55 of 76, 72%) were initially disqualified from their sport but subsequently opted for unrestricted RTP after comprehensive clinical evaluation and SDM. To date, (mean follow-up 7 ± 6 years), only 1 exercise-related (1.3%) and 2 nonexercise-related GHD-associated adverse cardiac events occurred. There have been no fatalities during follow-up.

CONCLUSIONS

This is the first study describing the experience of athletes with a known SCD-predisposing GHD who are competing at the elite level. After careful evaluation, risk stratification, and tailoring of their GHD therapy, RTP following SDM appears associated with low, nonfatal events rates at elite levels of sport.

Fatal Cardiac Arrhythmias During Electronic Gaming in Patients With Genetically Mediated Heart Diseases

BACKGROUND

Recently, electronic gaming has been reported as a precipitant of life-threatening cardiac arrhythmias in susceptible individuals. However, the prevalence of cardiac events in genetic heart diseases (GHDs) in the setting of electronic gaming has not been established.

OBJECTIVES

In this study, we sought to define the prevalence of cardiac events occurring in the setting of electronic gaming in GHDs.

METHODS

Retrospective review of all patients evaluated and treated at Mayo Clinic's genetic heart rhythm clinic from July 2000 to November 2022 was performed to identify patients with a history of playing electronic games at the time of their cardiac event. Cardiac event was used to define events occurring before diagnosis, and breakthrough cardiac event (BCE) was used for events occurring after diagnosis.

RESULTS

Of the 3,370 patients with a GHD (mean age at first evaluation 27 ± 19 years, 55% female), 1,079 (32%) had a cardiac event before diagnosis, with 5 patients (0.5%) having an electronic gaming-associated event (3 catecholaminergic polymorphic ventricular tachycardia, 1 long QT syndrome, and 1 premature ventricular contraction-triggered ventricular fibrillation). After diagnosis and treatment, 431 patients (13%) experienced ≥1 BCE during follow-up, of which 1 electronic gaming-associated BCE (0.2%) occurred in a patient with catecholamine-sensitive right outflow tract ventricular tachycardia.

CONCLUSIONS

Although anecdotal cases of electronic gaming-associated life-threatening arrhythmias have been reported, in this largest single-center study to date, we show that these are extremely rare occurrences. While electronic gaming can have adverse health consequences, the threat of electronic gaming-triggered sudden death should not be used to try to curb time spent gaming.

Association Between Syncope Trigger Type and Risk of Subsequent Life-Threatening Events in Patients With Long QT Syndrome

IMPORTANCE

Syncope is the most powerful predictor for subsequent life-threatening events (LTEs) in patients with congenital long QT syndrome (LQTS). Whether distinct syncope triggers are associated with differential subsequent risk of LTEs is unknown.

OBJECTIVE

To evaluate the association between adrenergic (AD)- and nonadrenergic (non-AD)-triggered syncopal events and the risk of subsequent LTEs in patients with LQT types 1 to 3 (LQT1-3).

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study included data from 5 international LQTS registries (Rochester, New York; the Mayo Clinic, Rochester, Minnesota; Israel, the Netherlands, and Japan). The study population comprised 2938 patients with genetically confirmed LQT1, LQT2, or LQT3 stemming from a single LQTS-causative variant. Patients were enrolled from July 1979 to July 2021.

EXPOSURES

Syncope by AD and non-AD triggers.

MAIN OUTCOMES AND MEASURES

The primary end point was the first occurrence of an LTE. Multivariate Cox regression was used to determine the association of AD- or non-AD-triggered syncope on the risk of subsequent LTE by genotype. Separate analysis was performed in patients with β-blockers.

RESULTS

A total of 2938 patients were included (mean [SD] age at enrollment, 29 [7] years; 1645 [56%] female). In 1331 patients with LQT1, a first syncope occurred in 365 (27%) and was induced mostly with AD triggers (243 [67%]). Syncope preceded 43 subsequent LTEs (68%). Syncopal episodes associated with AD triggers were associated with the highest risk of subsequent LTE (hazard ratio [HR], 7.61; 95% CI, 4.18-14.20; P < .001), whereas the risk associated with syncopal events due to non-AD triggers was statistically nonsignificant (HR, 1.50; 95% CI, 0.21-4.77; P = .97). In 1106 patients with LQT2, a first syncope occurred in 283 (26%) and was associated with AD and non-AD triggers in 106 (37%) and 177 (63%), respectively. Syncope preceded 55 LTEs (56%). Both AD- and non-AD-triggered syncope were associated with a greater than 3-fold increased risk of subsequent LTE (HR, 3.07; 95% CI, 1.66-5.67; P ≤ .001 and HR, 3.45, 95% CI, 1.96-6.06; P ≤ .001, respectively). In contrast, in 501 patients with LQT3, LTE was preceded by a syncopal episode in 7 (12%). In patients with LQT1 and LQT2, treatment with β-blockers following a syncopal event was associated with a significant reduction in the risk of subsequent LTEs. The rate of breakthrough events during treatment with β-blockers was significantly higher among those treated with selective agents vs nonselective agents.

CONCLUSION AND RELEVANCE

In this study, trigger-specific syncope in LQTS patients was associated with differential risk of subsequent LTE and response to β-blocker therapy.

Clinical course of patients with hypertrophic cardiomyopathy away from tertiary referral care

AIMS

Data on the clinical course of hypertrophic cardiomyopathy (HCM) are mainly derived from tertiary HCM centre studies, and knowledge of clinical outcomes of patients leaving specialty care and returning to local physicians is limited due to gaps between clinical encounters or complete loss of follow-up. This survey aims to describe the clinical course of HCM in patients following their evaluation at a tertiary referral centre.

METHODS AND RESULTS

A comprehensive outcomes survey was developed and sent to 4495 eligible patients with HCM previously evaluated at Mayo Clinic. Questions assessed general well-being, New York Heart Association class, procedures performed, and probable HCM-triggered ventricular arrhythmic events (VAEs) since last visit. In total, 2058 patients (mean age 63 ± 15 years; 42% female) responded to the survey covering a total of 10 510 patient-years with an average of 5.4 ± 6.4 years of follow-up since their last on-campus/virtual visit to Mayo Clinic. During their time away from specialty care, 20% of patients reported having cardiac-related hospitalizations and 25% reported having cardiac-related procedures. Similar to high-risk referral cohorts, 5% of patients reported VAEs with an event rate of 0.98 events/100 patient-years. The prevalence of atrial fibrillation, syncope, pre-syncope, cardiac-related hospitalizations, and VAEs during time away from specialty care increased significantly with increasing New York Heart Association class (P < 0.001).

CONCLUSIONS

Acknowledging ascertainment bias, the clinical course of patients away from tertiary care may be more severe than previously anticipated. Among those with exertional symptoms, HCM-related morbidity increased substantially. Higher risk HCM patients should remain in contact with HCM specialty care.

Multi-Omic Architecture of Obstructive Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is characterized by asymmetric left ventricular hypertrophy. Currently, hypertrophy pathways responsible for HCM have not been fully elucidated. Their identification could serve as a nidus for the generation of novel therapeutics aimed at halting disease development or progression. Herein, we performed a comprehensive multi-omic characterization of hypertrophy pathways in HCM.

METHODS

Flash-frozen cardiac tissues were collected from genotyped HCM patients (n=97) undergoing surgical myectomy and tissue from 23 controls. RNA sequencing and mass spectrometry-enabled deep proteome and phosphoproteomic assessment were performed. Rigorous differential expression, gene set enrichment, and pathway analyses were performed to characterize HCM-mediated alterations with emphasis on hypertrophy pathways.

RESULTS

We identified transcriptional dysregulation with 1246 (8%) differentially expressed genes and elucidated downregulation of 10 hypertrophy pathways. Deep proteomic analysis identified 411 proteins (9%) that differed between HCM and controls with strong dysregulation of metabolic pathways. Seven hypertrophy pathways were upregulated with antagonistic upregulation of 5 of 10 hypertrophy pathways shown to be downregulated in the transcriptome. Most upregulated hypertrophy pathways encompassed the RAS-MAPK signaling cascade. Phosphoproteomic analysis demonstrated hyperphosphorylation of the RAS-MAPK system suggesting activation of this signaling cascade. There was a common transcriptomic and proteomic profile regardless of genotype.

CONCLUSIONS

At time of surgical myectomy, the ventricular proteome, independent of genotype, reveals widespread upregulation and activation of hypertrophy pathways, mainly involving the RAS-MAPK signaling cascade. In addition, there is a counterregulatory transcriptional downregulation of the same pathways. RAS-MAPK activation may serve a crucial role in hypertrophy observed in HCM.

Cardiopulmonary Exercise Testing in Athletes With Hypertrophic Cardiomyopathy

Patients with hypertrophic cardiomyopathy (HCM) have historically been restricted from athletic participation because of the perceived risk of sudden cardiac death. More contemporary research has highlighted the relative safety of competitive athletics with HCM. However, lack of published data on reference values for cardiopulmonary exercise testing (CPET) complicates clinical management and counseling on sports participation in the individual athlete. We conducted a single-center, retrospective cohort study to investigate CPET in athletes with HCM and clinical characteristics associated with objective measures of aerobic capacity. We identified 58 athletes with HCM (74% male, mean age 18 ± 3 years, mean left ventricular (LV) wall thickness 20 ± 7 mm). LV outflow tract obstruction was present in 22 (38%). A total of 15 (26%) athletes were taking a β blocker (BB), but only 4 (7%) reported exertional symptoms. Overall, exercise capacity was mildly reduced, with a peak myocardial oxygen consumption (peak VO₂) of 37.9 ml/min/kg (83% of predicted peak VO₂). Both LV outflow tract obstruction and BB use were associated with reduced exercise capacity. Limited peak heart rate was more common in athletes taking BB (47% vs 9%, p = 0.002). At a mean 5.6 years follow-up, 5 patients underwent myectomy (9%), and 8 (14%) received an implantable cardioverter defibrillator (ICD) for primary prevention. One individual with massive LV hypertrophy experienced recurrent ICD shocks for ventricular fibrillation and underwent myectomy 7 years after initial evaluation and was no longer participating in sports. There were no deaths over the follow-up period. In conclusion, the prognostic role of CPET remains unclear in athletes with HCM. Mildly reduced exercise capacity was common; however, reduced peak VO₂ did not correlate with symptom status or clinical outcomes. A significant proportion went on to require myectomy and/or ICD, thus highlighting the need for close follow-up. These data provide some initial insight into the clinical evaluation of "real world" athletes with HCM; however, further study is warranted to help guide shared decision-making, return-to-play discussions, and the potential long-term safety of competitive athletic participation.

Repeatability of ventricular arrhythmia characteristics on the exercise-stress test in RYR2-mediated catecholaminergic polymorphic ventricular tachycardia

AIMS

In catecholaminergic polymorphic ventricular tachycardia (CPVT), the exercise-stress test (EST) is the cornerstone for the diagnosis, risk stratification, and assessment of therapeutic efficacy, but its repeatability is unknown. We aimed to test the repeatability of ventricular arrhythmia characteristics on the EST in patients with CPVT.

METHODS AND RESULTS

EST-pairs (ESTs performed within 18 months between 2005 and 2021, on the same protocol, and without or on the exact same treatment) of patients with RYR2-mediated CPVT from two specialized centres were included. The primary endpoint was the repeatability of the maximum ventricular arrhythmia score [VAS: 0 for the absence of premature ventricular contractions (PVCs); 1 for isolated PVCs; 2 for bigeminal PVCs; 3 for couplets; and 4 for non-sustained ventricular tachycardia]. Secondary outcomes were the repeatability of the heart rate at the first PVC and the ΔVAS (the absolute difference in VAS between the EST-pairs). A total of 104 patients with 349 EST-pairs were included. The median duration between ESTs was 343 (interquartile range, 189-378) days. Sixty (17.2%) EST-pairs were off therapy. The repeatability of the VAS was moderate {Krippendorf α, 0.56 [95% confidence interval (CI), 0.48-0.64]}, and the repeatability of the heart rate at the first PVC was substantial [intra-class correlation coefficient, 0.78 (95% CI, 0.71-0.84)]. The use of medication was associated with a higher odds for a ΔVAS > 1 (odds ratio = 3.52; 95% CI, 2.46-4.57; P = 0.020).

CONCLUSION

The repeatability of ventricular arrhythmia characteristics was moderate to substantial. This underlines the need for multiple ESTs in CPVT patients and CPVT suspicious patients and it provides the framework for assessing the therapeutic efficacy of novel CPVT therapies.

Outcomes of Athletes With Genetic Heart Diseases and Implantable Cardioverter-Defibrillators Who Chose to Return to Play

OBJECTIVE

To evaluate outcomes for athletes with a genetic heart disease (GHD) and an implantable cardioverter-defibrillator (ICD) after return-to-play (RTP) approval.

PATIENTS AND METHODS

We conducted a retrospective review of athletes with GHD and an ICD who were evaluated and treated in Mayo Clinic's Genetic Heart Rhythm Clinic between July 2000 and July 2020. Data on frequency of GHD-associated breakthrough cardiac events (BCEs), inappropriate shocks, and ICD-related complications were collected and analyzed.

RESULTS

There were 125 (57 [45.6%] female) GHD-positive athletes with an ICD (mean age at RTP was 19.8±11.6 years); 56 of 125 (44.8%) had long QT syndrome. Overall, 42 ventricular fibrillation-terminating ICD therapies were given to 23 athletes (18.4%) over an average follow-up of 3.6±3.5 years. Athletes with an ICD were more likely to experience a BCE during athletic follow-up (n=28 of 125, 22.4%) compared with those without an ICD (n=4 of 533, 0.8%; P<.0001). The BCE rate for athletes with ICDs was 6.3 events per 100 athlete-years of follow-up; this included 5.1 ventricular fibrillation-terminating events per 100 athlete-years compared with 0.3 BCEs per 100 patient-years for athletes without ICDs. In total, 6 (4.8%) athletes experienced at least one inappropriate shock (1.34 per 100 athlete-years) and 28 (29.6%) athletes had at least one other device-related complication (5.02 per 100 patient-years). However, none of these other complications occurred during sports.

CONCLUSION

This 20-year single-center study provides the longest spanning retrospective review of outcomes for athletes with ICDs given RTP approval. For athletes with GHD and an ICD, no sports-associated deaths or reports of sports-related ICD damage occurred.

Natural language processing for identification of hypertrophic cardiomyopathy patients from cardiac magnetic resonance reports

Background

Cardiac magnetic resonance (CMR) imaging is important for diagnosis and risk stratification of hypertrophic cardiomyopathy (HCM) patients. However, collection of information from large numbers of CMR reports by manual review is time-consuming, error-prone and costly. Natural language processing (NLP) is an artificial intelligence method for automated extraction of information from narrative text including text in CMR reports in electronic health records (EHR). Our objective was to assess whether NLP can accurately extract diagnosis of HCM from CMR reports.

Methods

An NLP system with two tiers was developed for information extraction from narrative text in CMR reports; the first tier extracted information regarding HCM diagnosis while the second extracted categorical and numeric concepts for HCM classification. We randomly allocated 200 HCM patients with CMR reports from 2004 to 2018 into training (100 patients with 185 CMR reports) and testing sets (100 patients with 206 reports).

Results

NLP algorithms demonstrated very high performance compared to manual annotation. The algorithm to extract HCM diagnosis had accuracy of 0.99. The accuracy for categorical concepts included HCM morphologic subtype 0.99, systolic anterior motion of the mitral valve 0.96, mitral regurgitation 0.93, left ventricular (LV) obstruction 0.94, location of obstruction 0.92, apical pouch 0.98, LV delayed enhancement 0.93, left atrial enlargement 0.99 and right atrial enlargement 0.98. Accuracy for numeric concepts included maximal LV wall thickness 0.96, LV mass 0.99, LV mass index 0.98, LV ejection fraction 0.98 and right ventricular ejection fraction 0.99.

Conclusions

NLP identified and classified HCM from CMR narrative text reports with very high performance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12911-022-02017-y.

Wnt Signaling Interactor WTIP (Wilms Tumor Interacting Protein) Underlies Novel Mechanism for Cardiac Hypertrophy

BACKGROUND

The study of hypertrophic cardiomyopathy (HCM) can yield insight into the mechanisms underlying the complex trait of cardiac hypertrophy. To date, most genetic variants associated with HCM have been found in sarcomeric genes. Here, we describe a novel HCM-associated variant in the noncanonical Wnt signaling interactor WTIP (Wilms tumor interacting protein) and provide evidence of a role for WTIP in complex disease.

METHODS

In a family affected by HCM, we used exome sequencing and identity-by-descent analysis to identify a novel variant in WTIP (p.Y233F). We knocked down WTIP in isolated neonatal rat ventricular myocytes with lentivirally delivered short hairpin ribonucleic acids and in Danio rerio via morpholino injection. We performed weighted gene coexpression network analysis for WTIP in human cardiac tissue, as well as association analysis for WTIP variation and left ventricular hypertrophy. Finally, we generated induced pluripotent stem cell-derived cardiomyocytes from patient tissue, characterized size and calcium cycling, and determined the effect of verapamil treatment on calcium dynamics.

RESULTS

WTIP knockdown caused hypertrophy in neonatal rat ventricular myocytes and increased cardiac hypertrophy, peak calcium, and resting calcium in D rerio. Network analysis of human cardiac tissue indicated WTIP as a central coordinator of prohypertrophic networks, while common variation at the WTIP locus was associated with human left ventricular hypertrophy. Patient-derived WTIP p.Y233F-induced pluripotent stem cell-derived cardiomyocytes recapitulated cellular hypertrophy and increased resting calcium, which was ameliorated by verapamil.

CONCLUSIONS

We demonstrate that a novel genetic variant found in a family with HCM disrupts binding to a known Wnt signaling protein, misregulating cardiomyocyte calcium dynamics. Further, in orthogonal model systems, we show that expression of the gene WTIP is important in complex cardiac hypertrophy phenotypes. These findings, derived from the observation of a rare Mendelian disease variant, uncover a novel disease mechanism with implications across diverse forms of cardiac hypertrophy.

Spectrum and Prevalence of Side Effects and Complications with Guideline Directed Therapies for Congenital Long QT Syndrome

BACKGROUND

Beta blockers (BBs), sodium channel blockers (SCBs), left cardiac sympathetic denervation (LCSD), and implantable cardioverter defibrillators (ICDs) are used to prevent or counter long QT syndrome (LQTS)-triggered syncope, seizures, and sudden cardiac death (SCD). The spectrum and extent of side effects/complications associated with these guideline-directed therapies (GDTs) remain unknown.

OBJECTIVE

Identify the types/prevalence of treatment-associated side effects/complications for patients with the most common LQTS subtypes following GDT.

METHODS

Retrospective analysis was performed on 1310 patients with type 1, 2 or 3 LQTS (LQT1-LQT3) evaluated in Mayo Clinic's Windland Smith Rice Genetic Heart Rhythm Clinic (average age at diagnosis 22±18 years; average treated follow-up 5±5 years) and treated with ≥1 of the common GDTs for LQTS.

RESULTS

BBs were used in 1102 (84%), SCBs in 104 (8%), LCSD in 197 (15%), and an ICD in 251 (19%) patients. Overall, 54% of patients reported at least one treatment-associated side effect/complication. 490/1102 (44%) patients treated with BBs reported side effects with fatigue (381; 35%) being most common. 28/104 (27%) SCB-treated patients reported side effects, most common being GI distress/vomiting (18, 17%). 80/197 (41%) patients reported side effects after LCSD, most reporting neuropathic pain (57; 29%). 129/251 (51%) patients experienced ≥1 complication after ICD implantation, including inappropriate shocks (46, 18%).

CONCLUSION

Although LQTS-triggered SCD is uncommon in the properly treated patient, this study demonstrates that contemporary GDTs for LQTS are not innocuous. Their treatment-related side effects are not trivial and should compel an ongoing quest for new LQTS therapies.

A phenotype-enhanced variant classification framework to decrease the burden of missense variants of uncertain significance in type 1 long QT syndrome

BACKGROUND

Pathogenic/likely pathogenic (P/LP) variants in the KCNQ1-encoded Kv7.1 potassium channel cause type 1 long QT syndrome (LQT1). Despite the revamped 2015 American College of Medical Genetics (ACMG) variant interpretation guidelines, the burden of KCNQ1 variants of uncertain significance (VUS) in patients with LQTS remains ∼30%.

OBJECTIVE

The purpose of this study was to determine whether a phenotype-enhanced (PE) variant classification approach could reduce the VUS burden in LQTS genetic testing.

METHODS

Retrospective analysis was performed on 79 KCNQ1 missense variants in 356 patients from Mayo Clinic and an independent cohort of 42 variants in 225 patients from Amsterdam University Medical Center (UMC). Each variant was classified initially using the ACMG guidelines and then readjudicated using a PE-ACMG framework that incorporated the LQTS clinical diagnostic Schwartz score plus 4 "LQT1-defining features": broad-based/slow upstroke T waves, syncope/seizure during exertion, swimming-associated events, and a maladaptive LQT1 treadmill stress test.

RESULTS

According to the ACMG guidelines, Mayo Clinic variants were classified as follows: 17 of 79 P variants (22%), 34 of 79 LP variants (43%), and 28 of 79 VUS (35%). Similarly, for Amsterdam UMC, the variant distribution was 9 of 42 P variants (22%), 14 of 42 LP variants (33%), and 19 of 42 variants VUS (45%). After PE-ACMG readjudication, the total VUS burden decreased significantly from 28 (35%) to 13 (16%) (P = .0007) for Mayo Clinic and from 19 (45%) to 12 (29%) (P = .02) for Amsterdam UMC.

CONCLUSION

Phenotype-guided variant adjudication decreased significantly the VUS burden of LQT1 case-derived KCNQ1 missense variants in 2 independent cohorts. This study demonstrates the value of incorporating LQT1-specific phenotype/clinical data to aid in the interpretation of KCNQ1 missense variants identified during genetic testing for LQTS.

Detection of hypertrophic cardiomyopathy by an artificial intelligence electrocardiogram in children and adolescents

BACKGROUND

There is no established screening approach for hypertrophic cardiomyopathy (HCM). We recently developed an artificial intelligence (AI) model for the detection of HCM based on the 12‑lead electrocardiogram (AI-ECG) in adults. Here, we aimed to validate this approach of ECG-based HCM detection in pediatric patients (age ≤ 18 years).

METHODS

We identified a cohort of 300 children and adolescents with HCM (mean age 12.5 ± 4.6 years, male 68%) who had an ECG and echocardiogram at our institution. Patients were age- and sex-matched to 18,439 non-HCM controls. Diagnostic performance of the AI-ECG model for the detection of HCM was estimated using the previously identified optimal diagnostic threshold of 11% (the probability output derived by the model above which an ECG is considered to belong to an HCM patient).

RESULTS

Mean AI-ECG probabilities of HCM were 92% and 5% in the case and control groups, respectively. The area under the receiver operating characteristic curve (AUC) of the AI-ECG model for HCM detection was 0.98 (95% CI 0.98-0.99) with corresponding sensitivity 92% and specificity 95%. The positive and negative predictive values were 22% and 99%, respectively. The model performed similarly in males and females and in genotype-positive and genotype-negative HCM patients. Performance tended to be superior with increasing age. In the age subgroup <5 years, the test's AUC was 0.93. In comparison, the AUC was 0.99 in the age subgroup 15-18 years.

CONCLUSIONS

A deep-learning, AI model can detect pediatric HCM with high accuracy from the standard 12‑lead ECG.

Role of chronic continuous intravenous lidocaine in the clinical management of patients with malignant type 3 long QT syndrome

BACKGROUND

Type 3 long QT syndrome (LQT3) is caused by pathogenic, gain-of-function variants in SCN5A leading to a prolonged action potential, ventricular ectopy, and torsades de pointes. Treatment options include pharmacotherapy, cardiac denervation, and/or device therapy. Rarely, patients with malignant LQT3 require cardiac transplantation.

OBJECTIVE

The purpose of this study was to evaluate the role of chronic continuous intravenous (IV) lidocaine as a therapeutic option for select patients with LQT3 refractory to standard therapy.

METHODS

We performed a retrospective review of patients evaluated and treated at Mayo Clinic and identified 4 of 161 patients with LQT3 (2.5%) who were refractory to standard therapies and therefore treated with IV lidocaine.

RESULTS

There were 4 patients (2 female [50%]). The median age at first IV lidocaine infusion was 2 months (interquartile range 1.5-4.8 months), and the median cumulative duration on IV lidocaine was 11.5 months (interquartile range 8.7-17.8 months). The main indication for IV lidocaine in all patients was persistent ventricular arrhythmias. Before IV lidocaine, all patients received an implantable cardioverter-defibrillator, and while on intermittent IV lidocaine, all patients underwent bilateral cardiac sympathetic denervation. Additionally, 2 (50%) patients had cardiac ablation for premature ventricular complexes. In all patients, lidocaine infusion resulted in a significant reduction of LQT3-triggered cardiac events. The main side effects of IV lidocaine observed were dizziness (n = 2, 50%) and seizures (n = 2, 50%). During follow-up, 3 of 4 (75%) patients underwent orthotopic cardiac transplantation. The remaining patient continues to receive IV lidocaine bolus for rescue as needed.

CONCLUSION

For patients with LQT3 who are refractory to standard treatment, chronic IV lidocaine infusion can be used as a potential "bridge to transplant."

Return-to-Play for Athletes With Long QT Syndrome or Genetic Heart Diseases Predisposing to Sudden Death

BACKGROUND

Within the last 5 years, cardiac society guidelines have begun to acknowledge shared decision making (SDM) for the athlete with sudden cardiac death-predisposing genetic heart diseases (GHDs), such as long QT syndrome (LQTS), and the possibility for that athlete's return to play. Previously, international guidelines embraced a de facto disqualification for all such athletes including athletes with solely a positive genetic test in Europe.

OBJECTIVES

This study sought to examine the prevalence and outcomes of athletes with sudden cardiac death-predisposing GHDs, particularly LQTS, after their return to play.

METHODS

A retrospective review of the electronic medical record was performed on all athletes with GHD, with a primary analysis for those with LQTS, who were evaluated, risk stratified, and treated in Mayo Clinic's Windland Smith Rice Genetic Heart Rhythm Clinic by a single genetic cardiologist between July 1, 2000, and July 31, 2020.

RESULTS

There were 672 athletes with GHD overall including 494 athletes with LQTS (231 female athletes [46.8%]; mean age at diagnosis 14.8 ± 10.5 years; mean follow-up 4.2 ± 4.8 years) who were given return-to-play approval. Overall, 79 of 494 athletes with LQTS (16.0%) were symptomatic before diagnosis, and 58 (11.7%) had an implantable cardioverter-defibrillator. In 2,056 combined years of follow-up, there was no GHD-sports associated mortality. Instead, 29 patients (5.9%) had ≥1 nonlethal, LQTS-associated breakthrough cardiac event. Of those, 15 (3.0%) were athletes at the time of the breakthrough cardiac event, with 3 (0.6%) experiencing a sports-related breakthrough cardiac event, and 12 (2.4%) a non-sports-related event. Overall, the event rate was 1.16 nonlethal events per 100 athlete-years of follow-up.

CONCLUSIONS

This 20-year single center experience challenges the status quo of disqualification for all athletes with LQTS and provides additional observational evidence, albeit from a single center, in support of the more contemporary SDM approaches to this complex issue.

Risk Prediction in Women With Congenital Long QT Syndrome

Background

We aimed to provide personalized risk estimates for cardiac events (CEs) and life‐threatening events in women with either type 1 or type 2 long QT.

Methods and Results

The prognostic model was derived from the Rochester Long QT Syndrome Registry, comprising 767 women with type 1 long QT (n=404) and type 2 long QT (n=363) from age 15 through 60 years. The risk prediction model included the following variables: genotype/mutation location, QTc‐specific thresholds, history of syncope, and β‐blocker therapy. A model was developed with the end point of CEs (syncope, aborted cardiac arrest, or long QT syndrome–related sudden cardiac death), and was applied with the end point of life‐threatening events (aborted cardiac arrest, sudden cardiac death, or appropriate defibrillator shocks). External validation was performed with data from the Mayo Clinic Genetic Heart Rhythm Clinic (N=467; type 1 long QT [n=286] and type 2 long QT [n=181]). The cumulative follow‐up duration among the 767 enrolled women was 22 243 patient‐years, during which 323 patients (42%) experienced ≥1 CE. Based on genotype‐phenotype data, we identified 3 risk groups with 10‐year projected rates of CEs ranging from 15%, 29%, to 51%. The corresponding 10‐year projected rates of life‐threatening events were 2%, 5%, and 14%. C statistics for the prediction model for the 2 respective end points were 0.68 (95% CI 0.65–0.71) and 0.71 (95% CI 0.66–0.76). Corresponding C statistics for the model in the external validation Mayo Clinic cohort were 0.65 (95% CI 0.60–0.70) and 0.77 (95% CI 0.70–0.84).

Conclusions

This is the first risk prediction model that provides absolute risk estimates for CEs and life‐threatening events in women with type 1 or type 2 long QT based on personalized genotype‐phenotype data. The projected risk estimates can be used to guide female‐specific management in long QT syndrome.

Myocardial Histopathology in Patients With Obstructive Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is characterized by multiple pathological features including myocyte hypertrophy, myocyte disarray, and interstitial fibrosis.

OBJECTIVES

This study sought to correlate myocardial histopathology with clinical characteristics of patients with obstructive HCM and post-operative outcomes following septal myectomy.

METHODS

The authors reviewed the pathological findings of the myocardial specimens from 1,836 patients with obstructive HCM who underwent septal myectomy from 2000 to 2016. Myocyte hypertrophy, myocyte disarray, interstitial fibrosis, and endocardial thickening were graded and analyzed.

RESULTS

The median age at operation was 54.2 years (43.5 to 64.3 years), and 1,067 (58.1%) were men. A weak negative correlation between myocyte disarray and age at surgery was identified (ρ = -0.22; p < 0.001). Myocyte hypertrophy (p < 0.001), myocyte disarray (p < 0.001), and interstitial fibrosis (p < 0.001) were positively associated with implantable cardioverter-defibrillator implantation. Interstitial fibrosis (p < 0.001) and endocardial thickening (p < 0.001) were associated with atrial fibrillation pre-operatively. In the Cox survival model, older age (p < 0.001), lower degree of myocyte hypertrophy (severe vs. mild hazard ratio: 0.41; 95% confidence interval: 0.19 to 0.86; p = 0.040), and lower degree of endocardial thickening (moderate vs. mild hazard ratio: 0.75; 95% confidence interval: 0.58 to 0.97; p = 0.019) were independently associated with worse post-myectomy survival. Among 256 patients who had genotype analysis, patients with pathogenic or likely pathogenic variants (n = 62) had a greater degree of myocyte disarray (42% vs. 15% vs. 20%; p = 0.022). Notably, 13 patients with pathogenic or likely pathogenic genetic variants of HCM had no myocyte disarray.

CONCLUSIONS

Histopathology was associated with clinical manifestations including the age of disease onset and arrhythmias. Myocyte hypertrophy and endocardial thickening were negatively associated with post-myectomy mortality.

Use of Artificial Intelligence and Deep Neural Networks in Evaluation of Patients With Electrocardiographically Concealed Long QT Syndrome From the Surface 12-Lead Electrocardiogram

Importance

Long QT syndrome (LQTS) is characterized by prolongation of the QT interval and is associated with an increased risk of sudden cardiac death. However, although QT interval prolongation is the hallmark feature of LQTS, approximately 40% of patients with genetically confirmed LQTS have a normal corrected QT (QTc) at rest. Distinguishing patients with LQTS from those with a normal QTc is important to correctly diagnose disease, implement simple LQTS preventive measures, and initiate prophylactic therapy if necessary.

Objective

To determine whether artificial intelligence (AI) using deep neural networks is better than the QTc alone in distinguishing patients with concealed LQTS from those with a normal QTc using a 12-lead electrocardiogram (ECG).

Design, Setting, and Participants

A diagnostic case-control study was performed using all available 12-lead ECGs from 2059 patients presenting to a specialized genetic heart rhythm clinic. Patients were included if they had a definitive clinical and/or genetic diagnosis of type 1, 2, or 3 LQTS (LQT1, 2, or 3) or were seen because of an initial suspicion for LQTS but were discharged without this diagnosis. A multilayer convolutional neural network was used to classify patients based on a 10-second, 12-lead ECG, AI-enhanced ECG (AI-ECG). The convolutional neural network was trained using 60% of the patients, validated in 10% of the patients, and tested on the remaining patients (30%). The study was conducted from January 1, 1999, to December 31, 2018.

Main Outcomes and Measures

The goal of the study was to test the ability of the convolutional neural network to distinguish patients with LQTS from those who were evaluated for LQTS but discharged without this diagnosis, especially among patients with genetically confirmed LQTS but a normal QTc value at rest (referred to as genotype positive/phenotype negative LQTS, normal QT interval LQTS, or concealed LQTS).

Results

Of the 2059 patients included, 1180 were men (57%); mean (SD) age at first ECG was 21.6 (15.6) years. All 12-lead ECGs from 967 patients with LQTS and 1092 who were evaluated for LQTS but discharged without this diagnosis were included for AI-ECG analysis. Based on the ECG-derived QTc alone, patients were classified with an area under the curve (AUC) value of 0.824 (95% CI, 0.79-0.858); using AI-ECG, the AUC was 0.900 (95% CI, 0.876-0.925). Furthermore, in the subset of patients who had a normal resting QTc (<450 milliseconds), the QTc alone distinguished those with LQTS from those without LQTS with an AUC of 0.741 (95% CI, 0.689-0.794), whereas the AI-ECG increased this discrimination to an AUC of 0.863 (95% CI, 0.824-0.903). In addition, the AI-ECG was able to distinguish the 3 main genotypic subgroups (LQT1, LQT2, and LQT3) with an AUC of 0.921 (95% CI, 0.890-0.951) for LQT1 compared with LQT2 and 3, 0.944 (95% CI, 0.918-0.970) for LQT2 compared with LQT1 and 3, and 0.863 (95% CI, 0.792-0.934) for LQT3 compared with LQT1 and 2.

Conclusions and Relevance

In this study, the AI-ECG was found to distinguish patients with electrocardiographically concealed LQTS from those discharged without a diagnosis of LQTS and provide a nearly 80% accurate pregenetic test anticipation of LQTS genotype status. This model may aid in the detection of LQTS in patients presenting to an arrhythmia clinic and, with validation, may be the stepping stone to similar tools to be developed for use in the general population.

Artificial Intelligence-Enabled Assessment of the Heart Rate Corrected QT Interval Using a Mobile Electrocardiogram Device

BACKGROUND

Heart rate-corrected QT interval (QTc) prolongation, whether secondary to drugs, genetics including congenital long QT syndrome, and/or systemic diseases including SARS-CoV-2-mediated coronavirus disease 2019 (COVID-19), can predispose to ventricular arrhythmias and sudden cardiac death. Currently, QTc assessment and monitoring relies largely on 12-lead electrocardiography. As such, we sought to train and validate an artificial intelligence (AI)-enabled 12-lead ECG algorithm to determine the QTc, and then prospectively test this algorithm on tracings acquired from a mobile ECG (mECG) device in a population enriched for repolarization abnormalities.

METHODS

Using >1.6 million 12-lead ECGs from 538 200 patients, a deep neural network (DNN) was derived (patients for training, n = 250 767; patients for testing, n = 107 920) and validated (n = 179 513 patients) to predict the QTc using cardiologist-overread QTc values as the "gold standard". The ability of this DNN to detect clinically-relevant QTc prolongation (eg, QTc ≥500 ms) was then tested prospectively on 686 patients with genetic heart disease (50% with long QT syndrome) with QTc values obtained from both a 12-lead ECG and a prototype mECG device equivalent to the commercially-available AliveCor KardiaMobile 6L.

RESULTS

In the validation sample, strong agreement was observed between human over-read and DNN-predicted QTc values (-1.76±23.14 ms). Similarly, within the prospective, genetic heart disease-enriched dataset, the difference between DNN-predicted QTc values derived from mECG tracings and those annotated from 12-lead ECGs by a QT expert (-0.45±24.73 ms) and a commercial core ECG laboratory [10.52±25.64 ms] was nominal. When applied to mECG tracings, the DNN's ability to detect a QTc value ≥500 ms yielded an area under the curve, sensitivity, and specificity of 0.97, 80.0%, and 94.4%, respectively.

CONCLUSIONS

Using smartphone-enabled electrodes, an AI DNN can predict accurately the QTc of a standard 12-lead ECG. QTc estimation from an AI-enabled mECG device may provide a cost-effective means of screening for both acquired and congenital long QT syndrome in a variety of clinical settings where standard 12-lead electrocardiography is not accessible or cost-effective.

Suppression-Replacement KCNQ1 Gene Therapy for Type 1 Long QT Syndrome

BACKGROUND

Type 1 long QT syndrome (LQT1) is caused by loss-of-function variants in the KCNQ1-encoded K_v7.1 potassium channel α-subunit that is essential for cardiac repolarization, providing the slow delayed rectifier current. No current therapies target the molecular cause of LQT1.

METHODS

A dual-component suppression-and-replacement (SupRep) KCNQ1 gene therapy was created by cloning a KCNQ1 short hairpin RNA and a short hairpin RNA-immune KCNQ1 cDNA modified with synonymous variants in the short hairpin RNA target site, into a single construct. The ability of KCNQ1-SupRep gene therapy to suppress and replace LQT1-causative variants in KCNQ1 was evaluated by means of heterologous expression in TSA201 cells. For a human in vitro cardiac model, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) were generated from 4 patients with LQT1 (KCNQ1-Y171X, -V254M, -I567S, and -A344A/spl) and an unrelated healthy control. CRISPR-Cas9 corrected isogenic control iPSC-CMs were made for 2 LQT1 lines (correction of KCNQ1-V254M and KCNQ1-A344A/spl). FluoVolt voltage dye was used to measure the cardiac action potential duration (APD) in iPSC-CMs treated with KCNQ1-SupRep.

RESULTS

In TSA201 cells, KCNQ1-SupRep achieved mutation-independent suppression of wild-type KCNQ1 and 3 LQT1-causative variants (KCNQ1-Y171X, -V254M, and -I567S) with simultaneous replacement of short hairpin RNA-immune KCNQ1 as measured by allele-specific quantitative reverse transcription polymerase chain reaction and Western blot. Using FluoVolt voltage dye to measure the cardiac APD in the 4 LQT1 patient-derived iPSC-CMs, treatment with KCNQ1-SupRep resulted in shortening of the pathologically prolonged APD at both 90% and 50% repolarization, resulting in APD values similar to those of the 2 isogenic controls.

CONCLUSIONS

This study provides the first proof-of-principle gene therapy for complete correction of long QT syndrome. As a dual-component gene therapy vector, KCNQ1-SupRep successfully suppressed and replaced KCNQ1 to normal wild-type levels. In TSA201 cells, cotransfection of LQT1-causative variants and KCNQ1-SupRep caused mutation-independent suppression and replacement of KCNQ1. In LQT1 iPSC-CMs, KCNQ1-SupRep gene therapy shortened the APD, thereby eliminating the pathognomonic feature of LQT1.

Left Cardiac Sympathetic Denervation Monotherapy in Patients With Congenital Long QT Syndrome

Background:

Videoscopic left cardiac sympathetic denervation (LCSD) is an effective antifibrillatory, minimally invasive therapy for patients with potentially life-threatening arrhythmia syndromes like long QT syndrome (LQTS). Although initially used primarily for treatment intensification following documented LQTS-associated breakthrough cardiac events while on beta-blockers, LCSD as 1-time monotherapy for certain patients with LQTS requires further evaluation. We are presenting our early experience with LCSD monotherapy for carefully selected patients with LQTS.

Methods:

Among the 1400 patients evaluated and treated for LQTS, a retrospective review was performed on the 204 patients with LQTS who underwent LCSD at our institution since 2005 to identify the patients where the LCSD served as stand-alone, monotherapy. Clinical data on symptomatic status before diagnosis, clinical, and genetic diagnosis, and breakthrough cardiac events after diagnosis were analyzed to determine efficacy of LCSD monotherapy.

Result:

Overall, 64 of 204 patients (31%) were treated with LCSD alone (37 [58%] female, mean QTc 466±30 ms, 16 [25%] patients were symptomatic before diagnosis with a mean age at diagnosis 17.3±11.8 years, 5 had [8%] ≥1 breakthrough cardiac event after diagnosis, and mean age at LCSD was 21.1±11.4 years). The primary motivation for LCSD monotherapy was an unacceptable quality of life stemming from beta-blocker related side effects (ie, beta-blocker intolerance) in 56/64 patients (88%). The underlying LQTS genotype was LQT1 in 36 (56%) and LQT2 in 20 (31%). There were no significant LCSD-related surgical complications. With a mean follow-up of 2.7±2.4 years so far, only 3 patients have experienced a nonlethal, post-LCSD breakthrough cardiac event in 180 patient-years.

Conclusions:

LCSD may be a safe and effective stand-alone therapy for select patients who do not tolerate beta-blockers. However, LCSD is not curative and patient selection will be critical when potentially considering LCSD as monotherapy.

SCN5A Mutation Type and a Genetic Risk Score Associate Variably With Brugada Syndrome Phenotype in SCN5A Families

Supplemental Digital Content is available in the text.

Brugada syndrome (BrS) is characterized by the type 1 Brugada ECG pattern. Pathogenic rare variants in SCN5A (mutations) are identified in 20% of BrS families in whom incomplete penetrance and genotype-negative phenotype-positive individuals are observed. E1784K-SCN5A is the most common SCN5A mutation identified. We determined the association of a BrS genetic risk score (BrS-GRS) and SCN5A mutation type on BrS phenotype in BrS families with SCN5A mutations.

Implantable cardioverter-defibrillators in previously undiagnosed patients with catecholaminergic polymorphic ventricular tachycardia resuscitated from sudden cardiac arrest

AIMS

In patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), implantable cardioverter-defibrillator (ICD) shocks are sometimes ineffective and may even trigger fatal electrical storms. We assessed the efficacy and complications of ICDs placed in patients with CPVT who presented with a sentinel event of sudden cardiac arrest (SCA) while undiagnosed and therefore untreated.

METHODS AND RESULTS

We analysed 136 patients who presented with SCA and in whom CPVT was diagnosed subsequently, leading to the initiation of guideline-directed therapy, including β-blockers, flecainide, and/or left cardiac sympathetic denervation. An ICD was implanted in 79 patients (58.1%). The primary outcome of the study was sudden cardiac death (SCD). The secondary outcomes were composite outcomes of SCD, SCA, appropriate ICD shocks, and syncope. After a median follow-up of 4.8 years, SCD had occurred in three patients (3.8%) with an ICD and none of the patients without an ICD (P = 0.1). SCD, SCA, or appropriate ICD shocks occurred in 37 patients (46.8%) with an ICD and 9 patients (15.8%) without an ICD (P < 0.0001). Inappropriate ICD shocks occurred in 19 patients (24.7%) and other device-related complications in 22 patients (28.9%).

CONCLUSION

In previously undiagnosed patients with CPVT who presented with SCA, an ICD was not associated with improved survival. Instead, the ICD was associated with both a high rate of appropriate ICD shocks and inappropriate ICD shocks along with other device-related complications. Strict adherence to guideline-directed therapy without an ICD may provide adequate protection in these patients without all the potential disadvantages of an ICD.

Clinical Utility of a Phenotype-Enhanced MYH7 -Specific Variant Classification Framework in Hypertrophic Cardiomyopathy Genetic Testing

Background:

Missense variants in the MYH7 -encoded MYH7 (beta myosin heavy chain 7) represent a leading cause of hypertrophic cardiomyopathy (HCM). MYH7 -specific American College of Medical Genetics and Genomics (ACMG) variant classification guidelines were released recently but have yet to be assessed independently. We set out to assess the performance of the MYH7 -specific ACMG guidelines and determine if the addition of phenotype-enhanced criteria (PE-ACMG) using the HCM Genotype Predictor Score can further reduce the burden of variants of uncertain significance (VUS).

Methods:

Re-assessment was performed on 70 MYH7 -variants in 121 unique patients from Mayo Clinic, and an independent cohort of 54 variants in 70 patients from Royal Prince Alfred Hospital (Australia). Qualifying variants were re-adjudicated using both standard ACMG and MYH7 -ACMG guidelines, and HCM Genotype Predictor Score was used to provide a validated measure of strength of clinical phenotype to be incorporated into the MYH7 -ACMG framework.

Results:

Among Mayo Clinic identified variants, 11/70 (16%) were classified as pathogenic (P), 10/70 (14%) as likely pathogenic, and 49/70 (70%) as a VUS. A similar distribution was seen in the Australian patients (12/54 [22%] P, 12/54 [22%] likely pathogenic, and 30/54 [56%] VUS; P =not significant). Application of the MYH7 -ACMG resulted in a nonsignificant reduction of the VUS burden in both cohorts from 49/70 to 39/70 (56%; P =0.1; Mayo Clinic) and from 30/54 to 20/54 (37%; P =0.1; Australia). Using the combined PE-MYH7-ACMG framework, the VUS decreased significantly from 49 to 27 ( P <0.001, Mayo Clinic) and from 30 to 16 ( P <0.001; Australia).

Conclusions:

Use of the MYH7 -specific guidelines alone failed to significantly decrease VUS burden in 2 independent cohorts. However, a significant reduction in VUS burden was observed after the addition of phenotypic criteria. Using a patient’s strength of sarcomeric HCM phenotype for variant adjudication can increase significantly the clinical utility of genetic testing for patients with HCM.

An International Multicenter Evaluation of Inheritance Patterns, Arrhythmic Risks, and Underlying Mechanisms of CASQ2-Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

Genetic variants in calsequestrin-2 (CASQ2) cause an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT), although isolated reports have identified arrhythmic phenotypes among heterozygotes. Improved insight into the inheritance patterns, arrhythmic risks, and molecular mechanisms of CASQ2-CPVT was sought through an international multicenter collaboration.

METHODS

Genotype-phenotype segregation in CASQ2-CPVT families was assessed, and the impact of genotype on arrhythmic risk was evaluated using Cox regression models. Putative dominant CASQ2 missense variants and the established recessive CASQ2-p.R33Q variant were evaluated using oligomerization assays and their locations mapped to a recent CASQ2 filament structure.

RESULTS

A total of 112 individuals, including 36 CPVT probands (24 homozygotes/compound heterozygotes and 12 heterozygotes) and 76 family members possessing at least 1 presumed pathogenic CASQ2 variant, were identified. Among CASQ2 homozygotes and compound heterozygotes, clinical penetrance was 97.1% and 26 of 34 (76.5%) individuals had experienced a potentially fatal arrhythmic event with a median age of onset of 7 years (95% CI, 6-11). Fifty-one of 66 CASQ2 heterozygous family members had undergone clinical evaluation, and 17 of 51 (33.3%) met diagnostic criteria for CPVT. Relative to CASQ2 heterozygotes, CASQ2 homozygote/compound heterozygote genotype status in probands was associated with a 3.2-fold (95% CI, 1.3-8.0; P=0.013) increased hazard of a composite of cardiac syncope, aborted cardiac arrest, and sudden cardiac death, but a 38.8-fold (95% CI, 5.6-269.1; P<0.001) increased hazard in genotype-positive family members. In vitro turbidity assays revealed that p.R33Q and all 6 candidate dominant CASQ2 missense variants evaluated exhibited filamentation defects, but only p.R33Q convincingly failed to dimerize. Structural analysis revealed that 3 of these 6 putative dominant negative missense variants localized to an electronegative pocket considered critical for back-to-back binding of dimers.

CONCLUSIONS

This international multicenter study of CASQ2-CPVT redefines its heritability and confirms that pathogenic heterozygous CASQ2 variants may manifest with a CPVT phenotype, indicating a need to clinically screen these individuals. A dominant mode of inheritance appears intrinsic to certain missense variants because of their location and function within the CASQ2 filament structure.

Genotype Predicts Outcomes in Fetuses and Neonates With Severe Congenital Long QT Syndrome

OBJECTIVES

This study sought to determine the relationship between long QT syndrome (LQTS) subtype (LTQ1, LTQ2, LTQ3) and postnatal cardiac events (CEs).

BACKGROUND

LQTS presenting with 2:1 atrioventricular block or torsades de pointes in the fetus and/or neonate has been associated with risk for major CEs, but overall outcomes and predictors remain unknown.

METHODS

A retrospective study involving 25 international centers evaluated the course of fetuses/newborns diagnosed with congenital LQTS and either 2:1 atrioventricular block or torsades de pointes. The primary outcomes were age at first CE after dismissal from the newborn hospitalization and death and/or cardiac transplantation during follow-up. CE was defined as aborted cardiac arrest, appropriate shock from implantable cardioverter-defibrillator, or sudden cardiac death.

RESULTS

A total of 84 fetuses and/or neonates were identified with LQTS (12 as LQT1, 35 as LQT2, 37 as LQT3). Median gestational age at delivery was 37 weeks (interquartile range: 35 to 39 weeks) and age at hospital discharge was 3 weeks (interquartile range: 2 to 5 weeks). Fetal demise occurred in 2 and pre-discharge death in 1. Over a median of 5.2 years, there were 1 LQT1, 3 LQT2, and 23 LQT3 CEs (13 aborted cardiac arrests, 5 sudden cardiac deaths, and 9 appropriate shocks). One patient with LQT1 and 11 patients with LQT3 died or received cardiac transplant during follow-up. The only multivariate predictor of post-discharge CEs was LQT3 status (LQT3 vs. LQT2: hazard ratio: 8.4; 95% confidence interval: 2.6 to 38.9; p < 0.001), and LQT3, relative to LQT2, genotype predicted death and/or cardiac transplant (p < 0.001).

CONCLUSIONS

In this large multicenter study, fetuses and/or neonates with LQT3 but not those with LQT1 or LQT2 presenting with severe arrhythmias were at high risk of not only frequent, but lethal CEs.

Corrected QT Interval–Polygenic Risk Score and Its Contribution to Type 1, Type 2, and Type 3 Long-QT Syndrome in Probands and Genotype-Positive Family Members

Background:

Long-QT syndrome (LQTS) is characterized by a prolonged heart rate–corrected QT interval (QTc). Genome-wide association studies identified common genetic variants that collectively explain ≈8% to 10% of QTc variation in the general population.

Methods:

Overall, 423 patients with LQT1, LQT2, or LQT3 were genotyped for 61 QTc-associated genetic variants used in a prototype QTc–polygenic risk score (QTc-PRS). A weighted QTc-PRS (range, 0–154.8 ms) was calculated for each patient, and the FHS (Framingham Heart Study) population-based reference cohort (n=853).

Results:

The average QTc-PRS in LQTS was 88.0±7.2 and explained only ≈2.0% of the QTc variability. The QTc-PRS in LQTS probands (n=137; 89.3±6.8) was significantly greater than both FHS controls (87.2±7.4, difference-in-means±SE: 2.1±0.7, P <0.002) and LQTS genotype-positive family members (87.5±7.4, difference-in-mean, 1.8±.7, P <0.009). There was no difference in QTc-PRS between symptomatic (n=156, 88.6±7.3) and asymptomatic patients (n=267; 87.7±7.2, difference-in-mean, 0.9±0.7, P=0.15). LQTS patients with a QTc≥480 ms (n=120) had a significantly higher QTc-PRS (89.3±6.7) than patients with a QTc<480 ms (n=303, 87.6±7.4, difference-in-mean, 1.7±0.8, P <0.05). There was no difference in QTc-PRS or QTc between genotypes.

Conclusions:

The QTc-PRS explained <2% of the QTc variability in our LQT1, LQT2, and LQT3 cohort, contributing 5× less to their QTc value than in the general population. This prototype QTc-PRS does not distinguish/predict the clinical outcomes of individuals with LQTS.

Assessment and Validation of a Phenotype-Enhanced Variant Classification Framework to Promote or Demote RYR2 Missense Variants of Uncertain Significance

Background Many rare, potentially pathogenic, RYR2 variants identified in individuals with clinically definite catecholaminergic polymorphic ventricular tachycardia are classified ambiguously as variants of uncertain significance (VUS). We aimed to determine if a phenotype-enhanced variant classification approach could reduce the burden of RYR2 VUS encountered during clinical genetic testing. Methods This retrospective study was conducted in 84 RYR2-positive individuals from the Mayo Clinic (Rochester, MN) and validated in 149 RYR2-positive individuals from Amsterdam University Medical Center (Amsterdam, NL). Using a newly developed diagnostic scorecard, the pretest clinical probability of catecholaminergic polymorphic ventricular tachycardia was determined for all RYR2-positive individuals. Each RYR2 variant was then readjudicated using a phenotype-enhanced American College of Medical Genetics approach that incorporates new criteria that reflect the phenotypic strength associated with each individual RYR2 variant. Results Overall, 72 distinct RYR2 variants were identified among the 84 Mayo Clinic (39 unique) and 149 Amsterdam University Medical Center (30 unique) cases. Three variants were present in both cohorts. American College of Medical Genetics guidelines classified 47% of all RYR2 variants as VUS. In the Mayo Clinic cohort, readjudication using amended phenotype-enhanced American College of Medical Genetics standards dropped the VUS rate significantly (20/42 [48%] versus 3/42 [7%]; P<0.001) with 13/20 (65%) RYR2 VUS promoted to likely pathogenic and 4/20 (20%) demoted to likely benign. A similar drop in VUS rate (14/33 [42%] versus 3/33 [9%]; P=0.001) was observed in the Amsterdam University Medical Center validation cohort with 10/14 (71%) RYR2 VUS promoted to likely pathogenic and 1/14 (7%) demoted to likely benign. Conclusions This multicenter study illustrates the potential utility of phenotype-enhanced variant classification in catecholaminergic polymorphic ventricular tachycardia.

Marked Up-Regulation of ACE2 in Hearts of Patients With Obstructive Hypertrophic Cardiomyopathy: Implications for SARS-CoV-2-Mediated COVID-19

OBJECTIVE

To explore the transcriptomic differences between patients with hypertrophic cardiomyopathy (HCM) and controls.

PATIENTS AND METHODS

RNA was extracted from cardiac tissue flash frozen at therapeutic surgical septal myectomy for 106 patients with HCM and 39 healthy donor hearts. Expression profiling of 37,846 genes was performed using the Illumina Human HT-12v3 Expression BeadChip. All patients with HCM were genotyped for pathogenic variants causing HCM. Technical validation was performed using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. This study was started on January 1, 1999, and final analysis was completed on April 20, 2020.

RESULTS

Overall, 22% of the transcriptome (8443 of 37,846 genes) was expressed differentially between HCM and control tissues. Analysis by genotype revealed that gene expression changes were similar among genotypic subgroups of HCM, with only 4% (1502 of 37,846) to 6% (2336 of 37,846) of the transcriptome exhibiting differential expression between genotypic subgroups. The qRT-PCR confirmed differential expression in 92% (11 of 12 genes) of tested transcripts. Notably, in the context of coronavirus disease 2019 (COVID-19), the transcript for angiotensin I converting enzyme 2 (ACE2), a negative regulator of the angiotensin system, was the single most up-regulated gene in HCM (fold-change, 3.53; q-value =1.30×10-23), which was confirmed by qRT-PCR in triplicate (fold change, 3.78; P=5.22×10-4), and Western blot confirmed greater than 5-fold overexpression of ACE2 protein (fold change, 5.34; P=1.66×10-6).

CONCLUSION

More than 20% of the transcriptome is expressed differentially between HCM and control tissues. Importantly, ACE2 was the most up-regulated gene in HCM, indicating perhaps the heart's compensatory effort to mount an antihypertrophic, antifibrotic response. However, given that the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses ACE2 for viral entry, this 5-fold increase in ACE2 protein may confer increased risk for COVID-19 manifestations and outcomes in patients with increased ACE2 transcript expression and protein levels in the heart.

Transethnic Genome-Wide Association Study Provides Insights in the Genetic Architecture and Heritability of Long QT Syndrome

Supplemental Digital Content is available in the text.

Long QT syndrome (LQTS) is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. A causal rare genetic variant with large effect size is identified in up to 80% of probands (genotype positive) and cascade family screening shows incomplete penetrance of genetic variants. Furthermore, a proportion of cases meeting diagnostic criteria for LQTS remain genetically elusive despite genetic testing of established genes (genotype negative). These observations raise the possibility that common genetic variants with small effect size contribute to the clinical picture of LQTS. This study aimed to characterize and quantify the contribution of common genetic variation to LQTS disease susceptibility.

International Triadin Knockout Syndrome Registry

BACKGROUND

Triadin knockout syndrome (TKOS) is a rare, inherited arrhythmia syndrome caused by recessive null mutations in TRDN-encoded cardiac triadin. Based previously on 5 triadin null patients, TKOS has been characterized by extensive T-wave inversions, transient QT prolongation, and severe disease expression of exercise-induced cardiac arrest in early childhood refractory to conventional therapy.

METHODS

We have established the International Triadin Knockout Syndrome Registry to include patients who have genetically proven homozygous/compound heterozygous TRDN null mutations. Clinical/genetic data were collected using an online survey generated through REDCap.

RESULTS

Currently, the International Triadin Knockout Syndrome Registry includes 21 patients (11 males, average age of 18 years) from 16 families. Twenty patients (95%) presented with either cardiac arrest (15, 71%) or syncope (5, 24%) at an average age of 3 years. Mild skeletal myopathy/proximal muscle weakness was noted in 6 (29%) patients. Of the 19 surviving patients, 16 (84%) exhibit T-wave inversions, and 10 (53%) have transient QT prolongation > 480 ms. Eight of 9 patients had ventricular ectopy on exercise stress testing. Thirteen (68%) patients have received implantable defibrillators. Despite various treatment strategies, 14 (74%) patients have had recurrent breakthrough cardiac events.

CONCLUSION

TKOS is a potentially lethal disease characterized by T-wave inversions in the precordial leads, transient QT prolongation in some, and recurrent ventricular arrhythmias at a young age despite aggressive treatment. Patients displaying this phenotype should undergo TRDN genetic testing as TKOS may be a cause for otherwise unexplained cardiac arrest in young children. As gene therapy advances, enrollment into the International Triadin Knockout Syndrome Registry is encouraged to better understand TKOS and to ready a well-characterized cohort for future TRDN gene therapy trials.

Heart Rate Recovery After Exercise Is Associated With Arrhythmic Events in Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

Background:

Risk stratification in catecholaminergic polymorphic ventricular tachycardia remains ill defined. Heart rate recovery (HRR) immediately after exercise is regulated by autonomic reflexes, particularly vagal tone, and may be associated with symptoms and ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia. Our objective was to evaluate whether HRR after maximal exercise on the exercise stress test (EST) is associated with symptoms and ventricular arrhythmias.

Methods:

In this retrospective observational study, we included patients ≤65 years of age with an EST without antiarrhythmic drugs who attained at least 80% of their age- and sex-predicted maximal HR. HRR in the recovery phase was calculated as the difference in heart rate (HR) at maximal exercise and at 1 minute in the recovery phase (ΔHRR1′).

Results:

We included 187 patients (median age, 36 years; 68 [36%] symptomatic before diagnosis). Pre-EST HR and maximal HR were equal among symptomatic and asymptomatic patients. Patients who were symptomatic before diagnosis had a greater ΔHRR1′ after maximal exercise (43 [interquartile range, 25–58] versus 25 [interquartile range, 19–34] beats/min; P <0.001). Corrected for age, sex, and relatedness, patients in the upper tertile for ΔHRR1′ had an odds ratio of 3.4 (95% CI, 1.6–7.4) of being symptomatic before diagnosis ( P <0.001). In addition, ΔHRR1′ was higher in patients with complex ventricular arrhythmias at EST off antiarrhythmic drugs (33 [interquartile range, 22–48] versus 27 [interquartile range, 20–36] beats/min; P =0.01). After diagnosis, patients with a ΔHRR1′ in the upper tertile of its distribution had significantly more arrhythmic events as compared with patients in the other tertiles ( P =0.045).

Conclusions:

Catecholaminergic polymorphic ventricular tachycardia patients with a larger HRR following exercise are more likely to be symptomatic and have complex ventricular arrhythmias during the first EST off antiarrhythmic drug.