Extracellular Kir2.1C122Y Mutant Upsets Kir2.1-PIP2 Bonds and Is Arrhythmogenic in Andersen-Tawil Syndrome

BACKGROUND

Andersen-Tawil syndrome type 1 is a rare heritable disease caused by mutations in the gene coding the strong inwardly rectifying K+ channel Kir2.1. The extracellular Cys (cysteine)122-to-Cys154 disulfide bond in the channel structure is crucial for proper folding but has not been associated with correct channel function at the membrane. We evaluated whether a human mutation at the Cys122-to-Cys154 disulfide bridge leads to Kir2.1 channel dysfunction and arrhythmias by reorganizing the overall Kir2.1 channel structure and destabilizing its open state.

METHODS

We identified a Kir2.1 loss-of-function mutation (c.366 A>T; p.Cys122Tyr) in an ATS1 family. To investigate its pathophysiological implications, we generated an AAV9-mediated cardiac-specific mouse model expressing the Kir2.1C122Y variant. We employed a multidisciplinary approach, integrating patch clamping and intracardiac stimulation, molecular biology techniques, molecular dynamics, and bioluminescence resonance energy transfer experiments.

RESULTS

Kir2.1C122Y mice recapitulated the ECG features of ATS1 independently of sex, including corrected QT prolongation, conduction defects, and increased arrhythmia susceptibility. Isolated Kir2.1C122Y cardiomyocytes showed significantly reduced inwardly rectifier K+ (IK1) and inward Na+ (INa) current densities independently of normal trafficking. Molecular dynamics predicted that the C122Y mutation provoked a conformational change over the 2000-ns simulation, characterized by a greater loss of hydrogen bonds between Kir2.1 and phosphatidylinositol 4,5-bisphosphate than wild type (WT). Therefore, the phosphatidylinositol 4,5-bisphosphate-binding pocket was destabilized, resulting in a lower conductance state compared with WT. Accordingly, on inside-out patch clamping, the C122Y mutation significantly blunted Kir2.1 sensitivity to increasing phosphatidylinositol 4,5-bisphosphate concentrations. In addition, the Kir2.1C122Y mutation resulted in channelosome degradation, demonstrating temporal instability of both Kir2.1 and NaV1.5 proteins.

CONCLUSIONS

The extracellular Cys122-to-Cys154 disulfide bond in the tridimensional Kir2.1 channel structure is essential for the channel function. We demonstrate that breaking disulfide bonds in the extracellular domain disrupts phosphatidylinositol 4,5-bisphosphate-dependent regulation, leading to channel dysfunction and defects in Kir2.1 energetic stability. The mutation also alters functional expression of the NaV1.5 channel and ultimately leads to conduction disturbances and life-threatening arrhythmia characteristic of Andersen-Tawil syndrome type 1.

Acute Adenoviral Infection Elicits an Arrhythmogenic Substrate Prior to Myocarditis

BACKGROUND

Viral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate before significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species specificity, models of infection are lacking, and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse adenovirus type-3 was previously reported as cardiotropic, yet it has not been utilized to understand the mechanisms of cardiac infection and pathology.

METHODS

We have developed mouse adenovirus type-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart before an appreciable immune response or gross cardiomyopathy.

RESULTS

Optical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against mouse adenovirus type-3-induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of mouse adenovirus type-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes, indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data.

CONCLUSIONS

Together, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

Circadian Regulation of Cardiac Arrhythmias and Electrophysiology

Circadian rhythms in physiology and behavior are ≈24-hour biological cycles regulated by internal biological clocks (ie, circadian clocks) that optimize organismal homeostasis in response to predictable environmental changes. These clocks are present in virtually all cells in the body, including cardiomyocytes. Many decades ago, clinicians and researchers became interested in studying daily patterns of triggers for sudden cardiac death, the incidence of sudden cardiac death, and cardiac arrhythmias. This review highlights historical and contemporary studies examining the role of day/night rhythms in the timing of cardiovascular events, delves into changes in the timing of these events over the last few decades, and discusses cardiovascular disease-specific differences in the timing of cardiovascular events. The current understanding of the environmental, behavioral, and circadian mechanisms that regulate cardiac electrophysiology is examined with a focus on the circadian regulation of cardiac ion channels and ion channel regulatory genes. Understanding the contribution of environmental, behavioral, and circadian rhythms on arrhythmia susceptibility and the incidence of sudden cardiac death will be essential in developing future chronotherapies.

Unraveling Complexities in Genetically Elusive Long QT Syndrome

Genetic testing has become standard of care for patients with long QT syndrome (LQTS), providing diagnostic, prognostic, and therapeutic information for both probands and their family members. However, up to a quarter of patients with LQTS do not have identifiable Mendelian pathogenic variants in the currently known LQTS-associated genes. This absence of genetic confirmation, intriguingly, does not lessen the severity of LQTS, with the prognosis in these gene-elusive patients with unequivocal LQTS mirroring genotype-positive patients in the limited data available. Such a conundrum instigates an exploration into the causes of corrected QT interval (QTc) prolongation in these cases, unveiling a broad spectrum of potential scenarios and mechanisms. These include multiple environmental influences on QTc prolongation, exercise-induced repolarization abnormalities, and the profound implications of the constantly evolving nature of genetic testing and variant interpretation. In addition, the rapid advances in genetics have the potential to uncover new causal genes, and polygenic risk factors may aid in the diagnosis of high-risk patients. Navigating this multifaceted landscape requires a systematic approach and expert knowledge, integrating the dynamic nature of genetics and patient-specific influences for accurate diagnosis, management, and counseling of patients. The role of a subspecialized expert cardiogenetic clinic is paramount in evaluation to navigate this complexity. Amid these intricate aspects, this review outlines potential causes of gene-elusive LQTS. It also provides an outline for the evaluation of patients with negative and inconclusive genetic test results and underscores the need for ongoing adaptation and reassessment in our understanding of LQTS, as the complexities of gene-elusive LQTS are increasingly deciphered.

Sudden Cardiac Death in National Collegiate Athletic Association Athletes: A 20-Year Study

BACKGROUND

Understanding the incidence, causes, and trends of sudden cardiac death (SCD) among young competitive athletes is critical to inform preventive policies.

METHODS

This study included National Collegiate Athletic Association athlete deaths during a 20-year time frame (July 1, 2002, through June 30, 2022). Athlete deaths were identified through 4 separate independent databases and search strategies (National Collegiate Athletic Association resolutions list, Parent Heart Watch database and media reports, National Center for Catastrophic Sports Injury Research database, and insurance claims). Autopsy reports and medical history were reviewed by an expert panel to adjudicate causes of SCD.

RESULTS

A total of 143 SCD cases in National Collegiate Athletic Association athletes were identified from 1102 total deaths. The National Collegiate Athletic Association resolutions list identified 117 of 143 (82%), the Parent Heart Watch database or media reports identified 89 of 143 (62%), the National Center for Catastrophic Sports Injury Research database identified 63 of 143 (44%), and insurance claims identified 27 of 143 (19%) SCD cases. The overall incidence of SCD was 1:63 682 athlete-years (95% CI, 1:54 065-1:75 010). Incidence was higher in male athletes than in female athletes (1:43 348 [95% CI, 1:36 228-1:51 867] versus 1:164 504 [95% CI, 1:110 552-1:244 787] athlete-years, respectively) and Black athletes compared with White athletes (1:26 704 [1:20 417-1:34 925] versus 1:74 581 [1:60 247-1:92 326] athlete-years, respectively). The highest incidence of SCD was among Division I male basketball players (1:8188 [White, 1:5848; Black, 1:7696 athlete-years]). The incidence rate for SCD decreased over the study period (5-year incidence rate ratio, 0.71 [95% CI, 0.61-0.82]), whereas the rate of noncardiovascular deaths remained stable (5-year incidence rate ratio, 0.98 [95% CI, 0.94-1.04]). Autopsy-negative sudden unexplained death (19.5%) was the most common postmortem examination finding, followed by idiopathic left ventricular hypertrophy or possible cardiomyopathy (16.9%) and hypertrophic cardiomyopathy (12.7%), in cases with enough information for adjudication (118 of 143). Eight cases of death were attributable to myocarditis over the study period (1 case from January 1, 2020, through June 30, 2022), with none attributed to COVID-19 infection. SCD events were exertional in 50% of cases. Exertional SCD was more common among those with coronary artery anomalies (100%) and arrhythmogenic cardiomyopathy (83%).

CONCLUSIONS

The incidence of SCD in college athletes has decreased. Male sex, Black race, and basketball are associated with a higher incidence of SCD.

Impact of serum haemoglobin-to-creatinine ratio after transcatheter aortic valve implantation

OBJECTIVE

The association between a combined anaemia and renal failure index and 1-year prognosis of patients undergoing transcatheter aortic valve implantation (TAVI) is unexplored. We aimed to investigate a simple risk score in patients undergoing TAVI.

METHODS

A total of 469 consecutive patients undergoing TAVI between 2015 and 2021 were enrolled. After excluding patients undergoing dialysis, the remaining 458 patients were classified according to three tertiles of the serum haemoglobin-to-creatinine (Hgb/Cr) ratio 1 day before TAVI. The primary clinical outcome measure was all-cause mortality and heart failure hospitalisation 1 year after TAVI.

RESULTS

In the first, second and third tertiles, the 1-year cumulative incidence of all-cause mortality was 16.9% versus 7.2% versus 2.0%, respectively (p<0.01), and that of heart failure hospitalisation was 10.7% versus 3.4% versus 0.7%, respectively (p<0.01). The indexes of the area under the curve of the Hgb/Cr ratio for all-cause mortality and heart failure hospitalisation 1 year after TAVI were both 0.73. Cut-off values were 10.1 for all-cause mortality 1 year after TAVI (OR, 4.78; 95% CI 2.43 to 9.74; p<0.01) and 10.4 for heart failure hospitalisation 1 year after TAVI (OR, 5.3; 95% CI 2.21 to 14.1; p<0.01). In the multivariate analysis, the Hgb/Cr ratio was an independent predictor of all-cause mortality and heart failure hospitalisation 1 year after TAVI.

CONCLUSIONS

Hgb/Cr ratio calculation 1 day before TAVI may help predict midterm all-cause mortality and heart failure hospitalisation in patients with severe aortic valve stenosis undergoing TAVI.

TRIAL REGISTRATION NUMBER

4143 (The Institutional Review Board of Kurashiki Central Hospital).

Asymptomatic Patients With Brugada ECG Pattern: Long-Term Prognosis From a Large Prospective Study

BACKGROUND

Brugada syndrome poses significant challenges in terms of risk stratification and management, particularly for asymptomatic patients who comprise the majority of individuals exhibiting Brugada ECG pattern (BrECG). The aim of this study was to evaluate the long-term prognosis of a large cohort of asymptomatic patients with BrECG.

METHODS

Asymptomatic patients with BrECG (1149) were consecutively collected from 2 Italian centers and followed-up at least annually for 2 to 22 years. For the 539 asymptomatic patients (men, 433 [80%]; mean age, 46±13 years) with spontaneous type 1 documented on baseline ECG (87%) or 12-lead 24-hour Holter monitoring (13%), an electrophysiologic study (EPS) was proposed; for the 610 patients with drug-induced-only type 1 (men, 420 [69%]; mean age, 44±14 years), multiple ECGs and 12-lead Holter were advised in order to detect the occurrence of a spontaneous type-1 BrECG. Arrhythmic events were defined as sudden death or documented ventricular fibrillation or tachycardia.

RESULTS

Median follow-up was 6 (4-9) years. Seventeen (1.5%) arrhythmic events occurred in the overall asymptomatic population (corresponding to an event-rate of 0.2% per year), including 16 of 539 (0.4% per year) in patients with spontaneous type-1 BrECG and 1 of 610 in those with drug-induced type-1 BrECG (0.03% per year; P<0.001). EPS was performed in 339 (63%) patients with spontaneous type-1 BrECG. Patients with spontaneous type-1 BrECG and positive EPS had significantly higher event rates than patients with negative EPS (7 of 103 [0.7% per year] versus 4 of 236 [0.2% per year]; P=0.025). Among 200 patients who declined EPS, 5 events (0.4% per year) occurred. There was 1 device-related death.

CONCLUSIONS

The entire population of asymptomatic patients with BrECG exhibits a relatively low event rate per year, which is important in view of the long life expectancy of these young patients. The presence of spontaneous type-1 BrECG associated with positive EPS identifies a subgroup at higher risk. Asymptomatic patients with drug-induced-only BrECG have a minimal arrhythmic risk, but ongoing follow-up with 12-lead Holter monitoring is recommended to detect the appearance of spontaneous type-1 BrECG pattern.

Arrhythmia and Death Following Percutaneous Revascularization in Ischemic Left Ventricular Dysfunction: Prespecified Analyses From the REVIVED-BCIS2 Trial

BACKGROUND

Ventricular arrhythmia is an important cause of mortality in patients with ischemic left ventricular dysfunction. Revascularization with coronary artery bypass graft or percutaneous coronary intervention is often recommended for these patients before implantation of a cardiac defibrillator because it is assumed that this may reduce the incidence of fatal and potentially fatal ventricular arrhythmias, although this premise has not been evaluated in a randomized trial to date.

METHODS

Patients with severe left ventricular dysfunction, extensive coronary disease, and viable myocardium were randomly assigned to receive either percutaneous coronary intervention (PCI) plus optimal medical and device therapy (OMT) or OMT alone. The composite primary outcome was all-cause death or aborted sudden death (defined as an appropriate implantable cardioverter defibrillator therapy or a resuscitated cardiac arrest) at a minimum of 24 months, analyzed as time to first event on an intention-to-treat basis. Secondary outcomes included cardiovascular death or aborted sudden death, appropriate implantable cardioverter defibrillator (ICD) therapy or sustained ventricular arrhythmia, and number of appropriate ICD therapies.

RESULTS

Between August 28, 2013, and March 19, 2020, 700 patients were enrolled across 40 centers in the United Kingdom. A total of 347 patients were assigned to the PCI+OMT group and 353 to the OMT alone group. The mean age of participants was 69 years; 88% were male; 56% had hypertension; 41% had diabetes; and 53% had a clinical history of myocardial infarction. The median left ventricular ejection fraction was 28%; 53.1% had an implantable defibrillator inserted before randomization or during follow-up. All-cause death or aborted sudden death occurred in 144 patients (41.6%) in the PCI group and 142 patients (40.2%) in the OMT group (hazard ratio, 1.03 [95% CI, 0.82-1.30]; P=0.80). There was no between-group difference in the occurrence of any of the secondary outcomes.

CONCLUSIONS

PCI was not associated with a reduction in all-cause mortality or aborted sudden death. In patients with ischemic cardiomyopathy, PCI is not beneficial solely for the purpose of reducing potentially fatal ventricular arrhythmias.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifier: NCT01920048.

EFFECTS OF M101-AN EXTRACELLULAR HEMOGLOBIN-APPLIED DURING CARDIOPULMONARY RESUSCITATION: AN EXPERIMENTAL RODENT STUDY

ABSTRACT

During and immediately after cardiac arrest, cerebral oxygen delivery is impaired mainly by microthrombi and cerebral vasoconstriction. This may narrow capillaries so much that it might impede the flow of red blood cells and thus oxygen transport. The aim of this proof-of-concept study was to evaluate the effect of M101, an extracellular hemoglobin-based oxygen carrier (Hemarina SA, Morlaix, France) derived from Arenicola marina , applied during cardiac arrest in a rodent model, on markers of brain inflammation, brain damage, and regional cerebral oxygen saturation. Twenty-seven Wistar rats subjected to 6 min of asystolic cardiac arrest were infused M101 (300 mg/kg) or placebo (NaCl 0.9%) concomitantly with start of cardiopulmonary resuscitation. Brain oxygenation and five biomarkers of inflammation and brain damage (from blood, cerebrospinal fluid, and homogenates from four brain regions) were measured 8 h after return of spontaneous circulation. In these 21 different measurements, M101-treated animals were not significantly different from controls except for phospho-tau only in single cerebellum regions ( P = 0.048; ANOVA of all brain regions: P = 0.004). Arterial blood pressure increased significantly only at 4 to 8 min after return of spontaneous circulation ( P < 0.001) and acidosis decreased ( P = 0.009). While M101 applied during cardiac arrest did not significantly change inflammation or brain oxygenation, the data suggest cerebral damage reduction due to hypoxic brain injury, measured by phospho-tau. Global burden of ischemia appeared reduced because acidosis was less severe. Whether postcardiac arrest infusion of M101 improves brain oxygenation is unknown and needs to be investigated.

Ischemia in Anomalous Aortic Origin of a Right Coronary Artery: Large Pediatric Cohort Medium-Term Outcomes

BACKGROUND

Anomalous aortic origin of a right coronary artery may cause myocardial ischemia and sudden death in the young. Data on myocardial ischemia or longitudinal outcomes are sparse in pediatric anomalous aortic origin of a right coronary artery population.

METHODS

Patients <21 years with anomalous aortic origin of a right coronary artery were prospectively enrolled. Computerized tomography angiography defined morphology. Exercise stress test and stress perfusion imaging (sPI) were performed if >7 years or younger with concern for ischemia. High-risk features included intramural length, slit-like/hypoplastic ostium, exertional symptoms, or evidence of ischemia.

RESULTS

A total of 220 patients (60% males) were enrolled December 2012 to April 2020 at a median age 11.4 years (interquartile range, 6.1-14.5), including 168 (76%) with no/nonexertional symptoms (group 1) and 52 (24%) with exertional chest pain/syncope (group 2). Computerized tomography angiography was available in 189/220 (86%), exercise stress test in 164/220 (75%), and sPI in 169/220 (77%). Exercise stress test was positive in 2/164 (1.2%) patients in group 1, both had positive sPI. Inducible ischemia (sPI) was detected in 11/120 (9%) in group 1 and 9/49 (18%) in group 2 (P=0.09). Intramural length was similar in patients with/without ischemia (5 [interquartile range, 4-7] versus 5 [interquartile range, 4-7] mm; P=0.65). Surgery was recommended in 56/220 (26%) patients with high-risk features. In 52 surgical patients (38 unroofing, 14 reimplantation), all subjects were alive and have returned to exercise at last median follow-up of 4.6 (interquartile range, 2.3-6.5) years.

CONCLUSIONS

Anomalous aortic origin of a right coronary artery patients can present with inducible ischemia on sPI despite symptoms or intramural length. Exercise stress test is a poor predictor of ischemia and caution should be given to determine low-risk based solely on this assessment. All patients are alive at medium-term follow-up.

The Prevalence and Association of Exercise Test Abnormalities With Sudden Cardiac Death and Transplant-Free Survival in Childhood Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) can be associated with an abnormal exercise response. In adults with HCM, abnormal results on exercise stress testing are predictive of heart failure outcomes. Our goal was to determine whether an abnormal exercise response is associated with adverse outcomes in pediatric patients with HCM.

METHODS

In an international cohort study including 20 centers, phenotype-positive patients with primary HCM who were <18 years of age at diagnosis were included. Abnormal exercise response was defined as a blunted blood pressure response and new or worsened ST- or T-wave segment changes or complex ventricular ectopy. Sudden cardiac death (SCD) events were defined as a composite of SCD and aborted sudden cardiac arrest. Using Kaplan-Meier survival, competing outcomes, and Cox regression analyses, we analyzed the association of abnormal exercise test results with transplant and SCD event-free survival.

RESULTS

Of 724 eligible patients, 630 underwent at least 1 exercise test. There were no major differences in clinical characteristics between those with or without an exercise test. The median age at exercise testing was 13.8 years (interquartile range, 4.7 years); 78% were male and 39% were receiving beta-blockers. A total of 175 (28%) had abnormal test results. Patients with abnormal test results had more severe septal hypertrophy, higher left atrial diameter z scores, higher resting left ventricular outflow tract gradient, and higher frequency of myectomy compared with participants with normal test results (P<0.05). Compared with normal test results, abnormal test results were independently associated with lower 5-year transplant-free survival (97% versus 88%, respectively; P=0.005). Patients with exercise-induced ischemia were most likely to experience all-cause death or transplant (hazard ratio, 4.86 [95% CI, 1.69-13.99]), followed by those with an abnormal blood pressure response (hazard ratio, 3.19 [95% CI, 1.32-7.71]). Exercise-induced ischemia was also independently associated with lower SCD event-free survival (hazard ratio, 3.32 [95% CI, 1.27-8.70]). Exercise-induced ectopy was not associated with survival.

CONCLUSIONS

Exercise abnormalities are common in childhood HCM. An abnormal exercise test result was independently associated with lower transplant-free survival, especially in those with an ischemic or abnormal blood pressure response with exercise. Exercise-induced ischemia was also independently associated with SCD events. These findings argue for routine exercise testing in childhood HCM as part of ongoing risk assessment.

Association Between Income and Risk of Out-of-Hospital Cardiac Arrest: A Retrospective Cohort Study

BACKGROUND

Previous studies have observed a higher out-of-hospital cardiac arrest (OHCA) risk among lower socioeconomic groups. However, due to the cross-sectional and ecological designs used in these studies, the magnitude of these inequalities is uncertain. This study is the first to assess the individual-level association between income and OHCA using a large-scale longitudinal study.

METHODS

This retrospective cohort study followed 1 688 285 adults aged 25 and above, living in the catchment area of an OHCA registry in a Dutch province. OHCA cases (n=5493) were linked to demographic and income registries. Cox proportional hazard models were conducted to determine hazard ratios of OHCA for household and personal income quintiles, stratified by sex and age.

RESULTS

The total incidence of OHCA per 100 000 person years was 30.9 in women and 87.1 in men. A higher OHCA risk was observed with lower household and personal income. Compared with the highest household income quintile, the adjusted hazard ratios from the second highest to the lowest household income quintiles ranged from 1.24 (CI=1.01-1.51) to 1.75 (CI=1.46-2.10) in women and from 0.95 (CI=0.68-1.34) to 2.30 (CI=1.74-3.05) in men. For personal income, this ranged from 0.95 (CI=0.68-1.34) to 2.30 (CI=1.74-3.05) in women and between 1.28 (CI=1.16-1.42) and 1.68 (CI=1.48-1.89) in men. Comparable household and personal income gradients were found across age groups except in the highest (>84 years) age group. For example, household income in women aged 65 to 74 ranged from 1.25 (CI=1.02-1.52) to 1.65 (CI=1.36-2.00). Sensitivity analyses assessing the prevalence of comorbidities at baseline and different lengths of follow-up yielded similar estimates.

CONCLUSIONS

This study provides new evidence for a substantial increase in OHCA risk with lower income in different age and sex groups. Low-income groups are likely to be a suitable target for intervention strategies to reduce OHCA risk.

Repeated Syncope During Exercise as a Result of Anomalous Origin of Left Coronary Artery With Intramural Aortic Course in a Teenage Boy

Anomalous origin of the left coronary artery from the opposite sinus of Valsalva with an intramural aortic course (L-ACAOS-IM) can cause syncope, sometimes as a prodrome of lethal events, including sudden cardiac death, in young athletes. The detailed mechanism of syncope in patients with L-ACAOS-IM is still unclear. This case report describes a 17-year-old boy who presented to the hospital because of syncope following chest pain with increasing frequency during exercise, such as playing soccer and running. In a treadmill exercise test, a decrease in blood pressure was seen (from 99/56 mm Hg to 68/38 mm Hg); chest pain and faintness accompanied by ST-segment elevation in lead aVR and ST-segment depression at other leads on electrocardiography were noted. These findings and symptoms disappeared spontaneously within a few minutes while clinicians prepared for emergency medications. Coronary computed tomography angiography (CCTA) showed that the origin of the left coronary artery (LCA) was the opposite sinus of Valsalva, and the course of the LCA was through the aortic wall toward the left coronary sinus. He was diagnosed with L-ACAOS-IM. After surgical treatment by unroofing the intramural part of the LCA and reconstructing a neo-ostium, he no longer experienced syncope during exercise. This case suggests that low cardiac output caused by myocardial ischemia, not life-threatening arrythmia, is a main mechanism of syncope in patients with L-ACAOS-IM. Consideration should be given to performing CCTA before an exercise stress test for young patients with syncope and chest pain to avoid the risk of severe myocardial ischemia.

Recurrent Out-of-Hospital Sudden Cardiac Arrest: Prevalence and Clinical Factors

BACKGROUND

Despite improvements in management following survival from sudden cardiac arrest (SCA) and wide availability of implantable cardioverter defibrillators for secondary prevention, a subgroup of individuals will suffer multiple distinct episodes of SCA. The objective of this study was to characterize and evaluate the burden of recurrent out-of-hospital SCA among survivors of SCA in a single large US community.

METHODS

SCA cases were prospectively ascertained in the Oregon Sudden Unexpected Death Study. Individuals that experienced recurrent SCA were identified both prospectively and retrospectively.

RESULTS

We ascertained 6649 individuals with SCA (2002-2020) and 924 (14%) survived to hospital discharge. Of these, 88 survivors (10%) experienced recurrent SCA. Of the nonsurvivors (n=5725), 35 had suffered a recurrent SCA. Of the total 123 SCA cases with recurrent SCA, >60% occurred at least 1 year after the initial SCA (median 23 months, range: 6 days to 31 years). SCA occurred despite a secondary prevention implantable cardioverter defibrillator in 22% (n=26). Prevalence of coronary disease (36% versus 25%), hypertension (69% versus 43%), diabetes (44% versus 21%), and chronic kidney disease (35% versus 14%) was significantly higher in recurrent SCA versus single SCA survivors (n=80, P=0.01). Among individuals with no secondary prevention implantable cardioverter defibrillators before recurrent SCA, the majority had apparently reversible etiologies identified at initial SCA, with one-quarter undergoing coronary revascularization and over half diagnosed with noncoronary cardiac etiologies.

CONCLUSIONS

At least 10% of SCA survivors had recurrent SCA, and a large subgroup suffered their repeat SCA despite treatment for an apparently reversible etiology. A renewed focus on careful assessment of cardiac substrate as well as management of coronary disease, hypertension, diabetes, and chronic kidney disease in SCA survivors could reduce recurrent SCA.

Heart rate turbulence assessed through ergometry after myocardial infarction: a feasibility study

BACKGROUND

Coronary artery disease is an important cause of morbidity and mortality. The impact of ventricular arrhythmias with impaired cardiac vagal activity is one of the most recently studied prognostic factors. However, there are no studies evaluating the phenomenon of heart rate turbulence (HRT) during physical exertion.

OBJECTIVE

To study the behavior of HRT during exercise testing, among individuals after myocardial infarction.

DESIGN AND SETTING

Feasibility study conducted in a university hospital among individuals 4-6 weeks after myocardial infarction.

METHODS

All subjects underwent 24-hour Holter monitoring and ergometric stress testing. We considered that abnormal HRT was present if the turbulence onset was ≥ 0% or turbulence slope was ≤ 2.5 mm/relative risk interval.

RESULTS

All 32 subjects were asymptomatic. Their median age was 58 years (interquartile range 12.8) and 70% were male. Abnormal HRT was associated with ventricular dysfunction in this population. We found no differences regarding the behavior of HRT, in relation to age, gender, smoking, systemic arterial hypertension, diabetes mellitus or dyslipidemia. Ergometric stress testing detected premature ventricular beats (PVB) in approximately 44% of the examinations, and these occurred both during the active phase of effort and in the recovery period. The low occurrence of several isolated PVB in beta-blocked subjects made it difficult to perform statistical analysis to correlate HRT between ergometric and Holter testing.

CONCLUSION

The data obtained in this study do not support performing HRT through ergometric stress testing among patients who remain on beta-blockers post-myocardial infarction, for the purpose of assessing cardiac vagal activity.

Genetic Architecture of Acute Myocarditis and the Overlap With Inherited Cardiomyopathy

BACKGROUND

Acute myocarditis is an inflammatory condition that may herald the onset of dilated cardiomyopathy (DCM) or arrhythmogenic cardiomyopathy (ACM). We investigated the frequency and clinical consequences of DCM and ACM genetic variants in a population-based cohort of patients with acute myocarditis.

METHODS

This was a population-based cohort of 336 consecutive patients with acute myocarditis enrolled in London and Maastricht. All participants underwent targeted DNA sequencing for well-characterized cardiomyopathy-associated genes with comparison to healthy controls (n=1053) sequenced on the same platform. Case ascertainment in England was assessed against national hospital admission data. The primary outcome was all-cause mortality.

RESULTS

Variants that would be considered pathogenic if found in a patient with DCM or ACM were identified in 8% of myocarditis cases compared with <1% of healthy controls (P=0.0097). In the London cohort (n=230; median age, 33 years; 84% men), patients were representative of national myocarditis admissions (median age, 32 years; 71% men; 66% case ascertainment), and there was enrichment of rare truncating variants (tv) in ACM-associated genes (3.1% of cases versus 0.4% of controls; odds ratio, 8.2; P=0.001). This was driven predominantly by DSP-tv in patients with normal LV ejection fraction and ventricular arrhythmia. In Maastricht (n=106; median age, 54 years; 61% men), there was enrichment of rare truncating variants in DCM-associated genes, particularly TTN-tv, found in 7% (all with left ventricular ejection fraction <50%) compared with 1% in controls (odds ratio, 3.6; P=0.0116). Across both cohorts over a median of 5.0 years (interquartile range, 3.9-7.8 years), all-cause mortality was 5.4%. Two-thirds of deaths were cardiovascular, attributable to worsening heart failure (92%) or sudden cardiac death (8%). The 5-year mortality risk was 3.3% in genotype-negative patients versus 11.1% for genotype-positive patients (Padjusted=0.08).

CONCLUSIONS

We identified DCM- or ACM-associated genetic variants in 8% of patients with acute myocarditis. This was dominated by the identification of DSP-tv in those with normal left ventricular ejection fraction and TTN-tv in those with reduced left ventricular ejection fraction. Despite differences between cohorts, these variants have clinical implications for treatment, risk stratification, and family screening. Genetic counseling and testing should be considered in patients with acute myocarditis to help reassure the majority while improving the management of those with an underlying genetic variant.

Incidence of Sudden Cardiac Death and Life-Threatening Arrhythmias in Clinically Manifest Cardiac Sarcoidosis With and Without Current Indications for an Implantable Cardioverter Defibrillator

BACKGROUND

Cardiac sarcoidosis (CS) predisposes to sudden cardiac death (SCD). Guidelines for implantable cardioverter defibrillators (ICDs) in CS have been issued by the Heart Rhythm Society in 2014 and the American College of Cardiology/American Heart Association/Heart Rhythm Society consortium in 2017. How well they discriminate high from low risk remains unknown.

METHODS

We analyzed the data of 398 patients with CS detected in Finland from 1988 through 2017. All had clinical cardiac manifestations. Histological diagnosis was myocardial in 193 patients (definite CS) and extracardiac in 205 (probable CS). Patients with and without Class I or IIa ICD indications at presentation were identified, and subsequent occurrences of SCD (fatal or aborted) and sustained ventricular tachycardia were recorded, as were ICD indications emerging first on follow-up.

RESULTS

Over a median of 4.8 years, 41 patients (10.3%) had fatal (n=8) or aborted (n=33) SCD, and 98 (24.6%) experienced SCD or sustained ventricular tachycardia as the first event. By the Heart Rhythm Society guideline, Class I or IIa ICD indications were present in 339 patients (85%) and absent in 59 (15%), of whom 264 (78%) and 30 (51%), respectively, received an ICD. Cumulative 5-year incidence of SCD was 10.7% (95% CI, 7.4%-15.4%) in patients with ICD indications versus 4.8% (95% CI, 1.2%-19.1%) in those without (χ2=1.834, P=0.176). The corresponding rates of SCD were 13.8% (95% CI, 9.1%-21.0%) versus 6.3% (95% CI, 0.7%-54.0%; χ2=0.814, P=0.367) in definite CS and 7.6% (95% CI, 3.8%-15.1%) versus 3.3% (95% CI, 0.5%-22.9%; χ2=0.680, P=0.410) in probable CS. In multivariable regression analysis, SCD was predicted by definite histological diagnosis (P=0.033) but not by Class I or IIa ICD indications (P=0.210). In patients without ICD indications at presentation, 5-year incidence of SCD, sustained ventricular tachycardia, and emerging Class I or IIa indications was 53% (95% CI, 40%-71%). By the American College of Cardiology/American Heart Association/Heart Rhythm Society guideline, all patients with complete data (n=245) had Class I or IIa indications for ICD implantation.

CONCLUSIONS

Current ICD guidelines fail to distinguish a truly low-risk group of patients with clinically manifest CS, the 5-year risk of SCD approaching 5% despite absent ICD indications. Further research is needed on prognostic factors, including the role of diagnostic histology. Meanwhile, all patients with CS presenting with clinical cardiac manifestations should be considered for an ICD implantation.

Frequency, Penetrance, and Variable Expressivity of Dilated Cardiomyopathy-Associated Putative Pathogenic Gene Variants in UK Biobank Participants

BACKGROUND

There is a paucity of data regarding the phenotype of dilated cardiomyopathy (DCM) gene variants in the general population. We aimed to determine the frequency and penetrance of DCM-associated putative pathogenic gene variants in a general adult population, with a focus on the expression of clinical and subclinical phenotype, including structural, functional, and arrhythmic disease features.

METHODS

UK Biobank participants who had undergone whole exome sequencing, ECG, and cardiovascular magnetic resonance imaging were selected for study. Three variant-calling strategies (1 primary and 2 secondary) were used to identify participants with putative pathogenic variants in 44 DCM genes. The observed phenotype was graded DCM (clinical or cardiovascular magnetic resonance diagnosis); early DCM features, including arrhythmia or conduction disease, isolated ventricular dilation, and hypokinetic nondilated cardiomyopathy; or phenotype-negative.

RESULTS

Among 18 665 individuals included in the study, 1463 (7.8%) possessed ≥1 putative pathogenic variant in 44 DCM genes by the main variant calling strategy. A clinical diagnosis of DCM was present in 0.34% and early DCM features in 5.7% of individuals with putative pathogenic variants. ECG and cardiovascular magnetic resonance analysis revealed evidence of subclinical DCM in an additional 1.6% and early DCM features in an additional 15.9% of individuals with putative pathogenic variants. Arrhythmias or conduction disease (15.2%) were the most common early DCM features, followed by hypokinetic nondilated cardiomyopathy (4%). The combined clinical/subclinical penetrance was ≤30% with all 3 variant filtering strategies. Clinical DCM was slightly more prevalent among participants with putative pathogenic variants in definitive/strong evidence genes as compared with those with variants in moderate/limited evidence genes.

CONCLUSIONS

In the UK Biobank, ≈1 of 6 of adults with putative pathogenic variants in DCM genes exhibited early DCM features potentially associated with DCM genotype, most commonly manifesting with arrhythmias in the absence of substantial ventricular dilation or dysfunction.

Role of Implantable Cardioverter Defibrillator in Heart Failure With Contemporary Medical Therapy

Implantable cardioverter defibrillator therapy is indicated in a subset of patients with heart failure with reduced ejection as primary prevention for sudden cardiac death. The advent of novel medical therapies including mineralocorticoid receptor antagonists, angiotensin receptor blocker/neprilysin inhibitors, and sodium-glucose transporter 2 inhibitor in the past 2 decades has revolutionized heart failure with reduced ejection management. Current guideline-directed medical therapy has reduced all-cause mortality and sudden cardiac death and confers a considerable improvement in left ventricular ejection fraction over a short period of time. However, there is limited evidence at present to suggest whether implantable cardioverter defibrillator therapy continues to have the same benefit in sudden cardiac death prevention at current left ventricular ejection fraction cutoff indications for patients on contemporary guideline-directed medical therapy for heart failure with reduced ejection. In this review, the authors propose in lieu of current evidence that it is reasonable to reevaluate indications for implantable cardioverter defibrillator therapy in patients on contemporary guideline-directed medical therapy for heart failure with reduced ejection.

DREAM-ICD-II Study

BACKGROUND

Regulatory authorities of most industrialized countries recommend 6 months of private driving restriction after implantation of a secondary prevention implantable cardioverter-defibrillator (ICD). These driving restrictions result in significant inconvenience and social implications. This study aimed to assess the incidence rate of appropriate device therapies in contemporary recipients of a secondary prevention ICD.

METHODS

This retrospective study at 3 Canadian tertiary care centers enrolled consecutive patients with new secondary prevention ICD implants between 2016 and 2020.

RESULTS

For a median of 760 days (324, 1190 days), 721 patients were followed up. The risk of recurrent ventricular arrhythmia was highest during the first 3 months after device insertion (34.4%) and decreased over time (10.6% between 3 and 6 months, 11.7% between 6 and 12 months). The corresponding incidence rate per 100 patient-days was 0.48 (95% CI, 0.35-0.64) at 90 days, 0.28 (95% CI, 0.17-0.45) at 180 days, and 0.21 (95% CI, 0.13-0.33) between 181 and 365 days after ICD insertion (P<0.001). The cumulative incidence of arrhythmic syncope resulting in sudden cardiac incapacitation was 1.8% within the first 90 days and subsequently dropped to 0.4% between 91 and 180 days (P<0.001) after ICD insertion.

CONCLUSIONS

The incidence rate of appropriate therapies resulting in sudden cardiac incapacitation in contemporary recipients of a secondary prevention ICD is much lower than previously reported and declines significantly after the first 3 months. Lowering driving restrictions to 3 months after the index cardiac event seems safe, and revision of existing guidelines should be considered in countries still adhering to a 6-month period. Existing restrictions for private driving after implantation of a secondary prevention ICD should be reconsidered.

Exome Sequencing Highlights a Potential Role for Concealed Cardiomyopathies in Youthful Sudden Cardiac Death

BACKGROUND

Sudden cardiac arrest (SCA) and sudden unexplained death (SUD) are feared sequelae of many genetic heart diseases. In rare circumstances, pathogenic variants in cardiomyopathy-susceptibility genes may result in electrical instability leading to SCA/SUD before any structural manifestations of underlying cardiomyopathy are evident.

METHODS

Collectively, 38 unexplained SCA survivors (21 males; mean age at SCA 26.4±13.1 years), 68 autopsy-inconclusive SUD cases (46 males; mean age at death 20.4±9.0 years) without disease-causative variants in the channelopathy genes, and 973 ostensibly healthy controls were included. Following exome sequencing, ultrarare (minor allele frequency ≤0.00005 in any ethnic group within Genome Aggregation Database [gnomAD, N=141 456 individuals]) nonsynonymous variants identified in 24 Clinical Genome Resource adjudicated definitive/strong evidence cardiomyopathy-susceptibility genes were analyzed. Eligible variants were adjudicated as pathogenic, likely pathogenic, or variant of uncertain significance in accordance with current American College of Medical Genetics and Genomics guidelines.

RESULTS

Overall, 7 out of 38 (18.4%) SCA survivors and 14 out of 68 (20.5%) autopsy-inconclusive, channelopathic-negative SUD cases had at least one pathogenic/likely pathogenic or a variant of uncertain significance nonsynonymous variant within a strong evidence, cardiomyopathy-susceptibility gene. Following American College of Medical Genetics and Genomics criterion variant adjudication, a pathogenic or likely pathogenic variant was identified in 3 out of 38 (7.9%; P=0.05) SCA survivors and 8 out of 68 (11.8%; P=0.0002) autopsy-inconclusive SUD cases compared to 20 out of 973 (2.1%) European controls. Interestingly, the yield of pathogenic/likely pathogenic variants was significantly greater in autopsy-inconclusive SUD cases with documented interstitial fibrosis (4/11, 36%) compared with only 4 out of 57 (7%, P<0.02) SUD cases without ventricular fibrosis.

CONCLUSIONS

Our data further supports the inclusion of strong evidence cardiomyopathy-susceptibility genes on the genetic testing panels used to evaluate unexplained SCA survivors and autopsy-inconclusive/negative SUD decedents. However, to avoid diagnostic miscues, the careful interpretation of genetic test results in patients without overt phenotypes is vital.

Nonsustained Ventricular Tachycardia Is Independently Associated With Sustained Ventricular Arrhythmias in Nonischemic Dilated Cardiomyopathy

BACKGROUND

Spontaneous nonsustained ventricular tachycardia (NSVT) on Holter, VT inducibility during electrophysiology study, and late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) have been associated with sustained ventricular arrhythmias (SVAs) in nonischemic dilated cardiomyopathy (DCM). This study aimed to analyze whether these parameters carry independent prognostic value for spontaneous SVA in DCM.

METHODS

Between 2011 and 2018, patients with the DCM clinical spectrum and documented SVA, suspected SVA, or considered to be at intermediate or high risk for SVA were enrolled in the prospective Leiden Nonischemic Cardiomyopathy Study. Patients underwent a comprehensive evaluation including 24-hour Holter, LGE-CMR, and electrophysiology study. Holters were assessed for the presence of NSVT (≥3 beats; rate, ≥120 bpm; lasting <30 s) and NSVT characteristics (coupling interval, duration, cycle length, morphology, regularity). Patients were followed at 6 to 12 monthly intervals.

RESULTS

Of all 115 patients (age, 59±12 years; 77% men; left ventricular ejection fraction, 33±13%; history of SVA, 36%; LGE in 63%; median LGE mass, 13 g; interquartile range, 8-23 g), 62 (54%) had NSVT on Holter, and sustained monomorphic VT was inducible in 34 of 114 patients (30%). NSVT was not associated with LGE on CMR or VT inducibility during electrophysiology study nor were its features (all P>0.05). During 4.0±1.8 years of follow-up, SVA occurred in 39 patients (34%). NSVT (HR, 4.47 [95% CI, 1.87-10.72]; P=0.001) and VT inducibility (HR, 3.08 [95% CI, 1.08-8.81]; P=0.036) were independently associated with SVA during follow-up. A bivariable model including only noninvasively acquired parameters also allowed identification of a high-risk subgroup (ie, those with both NSVT and LGE on CMR). The findings remained similar when only patients without prior SVA were included.

CONCLUSIONS

In patients with DCM, NSVT on Holter and VT inducibility during electrophysiology study predict SVA during follow-up independent of LGE on CMR. NSVTs may serve as an initiator, and sustained VT inducibility indicates the presence of the substrate for SVA in DCM. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01940081.

Implantable Cardioverter Defibrillators in Infants and Toddlers: Indications, Placement, Programming, and Outcomes

BACKGROUND

Limited data exist regarding implantable cardioverter defibrillator (ICD) usage in infants and toddlers. This study evaluates ICD placement indications, procedural techniques, programming strategies, and outcomes of ICDs in infants and toddlers.

METHODS

This is a single-center retrospective review of all patients ≤3 years old who received an ICD from 2009 to 2021.

RESULTS

Fifteen patients received an ICD at an age of 1.2 years (interquartile range [IQR], 0.1-2.4; 12 [80%] women; weight, 8.2 kg [IQR, 4.2-12.6]) and were followed for a median of 4.28 years (IQR, 1.40-5.53) or 64.2 patient-years. ICDs were placed for secondary prevention in 12 patients (80%). Diagnoses included 8 long-QT syndromes (53%), 4 idiopathic ventricular tachycardias/ventricular fibrillations (VFs; 27%), 1 recurrent ventricular tachycardia with cardiomyopathy (7%), 1 VF with left ventricular noncompaction (7%), and 1 catecholaminergic polymorphic ventricular tachycardia (7%). All implants were epicardial, with a coil in the pericardial space. Intraoperative defibrillation safety testing was attempted in 11 patients (73%), with VF induced in 8 (53%). Successful restoration of sinus rhythm was achieved in all tested patients with a median of 9 (IQR, 7.3-11.3) J or 0.90 (IQR, 0.68-1.04) J/kg. Complications consisted of 1 postoperative chylothorax and 3 episodes of feeding intolerance. VF detection was programmed to 250 (IQR, 240-250) ms with first shock delivering 10 (IQR, 5-15) J or 1.1 (IQR, 0.8-1.4) J/kg. Three patients (20%) received appropriate shocks for ventricular tachycardia/VF. No patient received an inappropriate shock. There were 2 (13%) ventricular lead fractures (at 2.6 and 4.2 years post-implant), 1 (7%) pocket-site infection, and 2 (13%) generator exchanges. All patients were alive, and 1 patient (7%) received a heart transplant.

CONCLUSIONS

ICDs can be safely and effectively placed for sudden death prevention in infants and toddlers with good midterm outcomes.

Multimodality Imaging in Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rare, heritable myocardial disease associated with the development of ventricular arrhythmias, heart failure, and sudden cardiac death in early adulthood. Multimodality imaging is a central component in the diagnosis and evaluation of ARVC. Diagnostic criteria established by an international task force in 2010 include noninvasive parameters from echocardiography and cardiac magnetic resonance imaging. These criteria identify right ventricular structural abnormalities, chamber and outflow tract dilation, and reduced right ventricular function as features of ARVC. Echocardiography is a widely available and cost-effective technique, and it is often selected for initial evaluation. Beyond fulfillment of diagnostic criteria, features such as abnormal tricuspid annular plane excursion, increased right ventricular basal diameter, and abnormal strain patterns have been described. 3-dimensional echocardiography may also expand opportunities for structural and functional assessment of ARVC. Cardiac magnetic resonance has the ability to assess morphological and functional cardiac features of ARVC and is also a core modality in evaluation, however, tissue characterization of the right ventricle is limited by spatial resolution and low specificity for detection of pathological changes. Nonetheless, the ability of cardiac magnetic resonance to identify left ventricular involvement, offer high negative predictive value, and provide a reproducible structural evaluation of the right ventricle enhance the ability and scope of the modality. In this review, the prognostic significance of multimodality imaging is outlined, including the supplemental value of multidetector computed tomography and nuclear imaging. Strengths and weaknesses of imaging techniques, as well as future direction of multimodality assessment, are also described.

Phenotypic Expression, Natural History, and Risk Stratification of Cardiomyopathy Caused by Filamin C Truncating Variants

BACKGROUND

Filamin C truncating variants (FLNCtv) cause a form of arrhythmogenic cardiomyopathy: the mode of presentation, natural history, and risk stratification of FLNCtv remain incompletely explored. We aimed to develop a risk profile for refractory heart failure and life-threatening arrhythmias in a multicenter cohort of FLNCtv carriers.

METHODS

FLNCtv carriers were identified from 10 tertiary care centers for genetic cardiomyopathies. Clinical and outcome data were compiled. Composite outcomes were all-cause mortality/heart transplantation/left ventricle assist device (D/HT/LVAD), nonarrhythmic death/HT/LVAD, and sudden cardiac death/major ventricular arrhythmias. Previously established cohorts of 46 patients with LMNA and 60 with DSP-related arrhythmogenic cardiomyopathies were used for prognostic comparison.

RESULTS

Eighty-five patients carrying FLNCtv were included (42±15 years, 53% men, 45% probands). Phenotypes were heterogeneous at presentation: 49% dilated cardiomyopathy, 25% arrhythmogenic left dominant cardiomyopathy, 3% arrhythmogenic right ventricular cardiomyopathy. Left ventricular ejection fraction was <50% in 64% of carriers and 34% had right ventricular fractional area changes (RVFAC=(right ventricular end-diastolic area - right ventricular end-systolic area)/right ventricular end-diastolic area) <35%. During follow-up (median time 61 months), 19 (22%) carriers experienced D/HT/LVAD, 13 (15%) experienced nonarrhythmic death/HT/LVAD, and 23 (27%) experienced sudden cardiac death/major ventricular arrhythmias. The sudden cardiac death/major ventricular arrhythmias incidence of FLNCtv carriers did not significantly differ from LMNA carriers and DSP carriers. In FLNCtv carriers, left ventricular ejection fraction was associated with the risk of D/HT/LVAD and nonarrhythmic death/HT/LVAD.

CONCLUSIONS

Among patients referred to tertiary referral centers, FLNCtv arrhythmogenic cardiomyopathy is phenotypically heterogeneous and characterized by a high risk of life-threatening arrhythmias, which does not seem to be associated with the severity of left ventricular dysfunction.

Inflammation and Immune Response in Arrhythmogenic Cardiomyopathy: State-of-the-Art Review

Arrhythmogenic cardiomyopathy (ACM) is a primary disease of the myocardium, predominantly caused by genetic defects in proteins of the cardiac intercalated disc, particularly, desmosomes. Transmission is mostly autosomal dominant with incomplete penetrance. ACM also has wide phenotype variability, ranging from premature ventricular contractions to sudden cardiac death and heart failure. Among other drivers and modulators of phenotype, inflammation in response to viral infection and immune triggers have been postulated to be an aggravator of cardiac myocyte damage and necrosis. This theory is supported by multiple pieces of evidence, including the presence of inflammatory infiltrates in more than two-thirds of ACM hearts, detection of different cardiotropic viruses in sporadic cases of ACM, the fact that patients with ACM often fulfill the histological criteria of active myocarditis, and the abundance of anti-desmoglein-2, antiheart, and anti-intercalated disk autoantibodies in patients with arrhythmogenic right ventricular cardiomyopathy. In keeping with the frequent familial occurrence of ACM, it has been proposed that, in addition to genetic predisposition to progressive myocardial damage, a heritable susceptibility to viral infections and immune reactions may explain familial clustering of ACM. Moreover, considerable in vitro and in vivo evidence implicates activated inflammatory signaling in ACM. Although the role of inflammation/immune response in ACM is not entirely clear, inflammation as a driver of phenotype and a potential target for mechanism-based therapy warrants further research. This review discusses the present evidence supporting the role of inflammatory and immune responses in ACM pathogenesis and proposes opportunities for translational and clinical investigation.

Coronary Artery Anomalies

Coronary artery anomalies (CAAs) are a group of congenital conditions characterized by abnormal origin or course of any of the 3 main epicardial coronary arteries. Although CAAs have been identified as a common underlying condition in young athletes with sudden cardiac death, the widespread use of invasive and noninvasive coronary imaging has led to increased recognition of CAAs among adults. CAAS are often discovered as an incidental finding during the diagnostic workup for ischemic heart disease. The clinical correlates and prognostic implication of CAAs remain poorly understood in this context, and guideline-recommended therapeutic choices are supported by a low level of scientific evidence. Several studies have examined whether assessment of CAA-related myocardial ischemia can improve risk stratification in these patients, suggesting that multimodality imaging and functional tests may be key in the management of CAAs. The aim of this review is to outline definitions, classification, and epidemiology of the most relevant CAAs, highlighting recent advances and the potential impact of multimodality evaluation, and to discuss current therapeutic opportunities.

Interpretation of Incidental Genetic Findings Localizing to Genes Associated With Cardiac Channelopathies and Cardiomyopathies

Recent advances in next-genetic sequencing technology have facilitated an expansion in the use of exome and genome sequencing in the research and clinical settings. While this has aided in the genetic diagnosis of individuals with atypical clinical presentations, there has been a marked increase in the number of incidentally identified variants of uncertain diagnostic significance in genes identified as clinically actionable by the American College of Medical Genetics guidelines. Approximately 20 of these genes are associated with cardiac diseases, which carry a significant risk of sudden cardiac death. While identification of at-risk individuals is paramount, increased discovery of incidental variants of uncertain diagnostic significance has placed a burden on the clinician tasked with determining the diagnostic significance of these findings. Herein, we describe the scope of this emerging problem using cardiovascular genetics to illustrate the challenges associated with variants of uncertain diagnostic significance interpretation. We review the evidence for diagnostic weight of these variants, discuss the role of clinical genetics providers in patient care, and put forward general recommendations about the interpretation of incidentally identified variants found with clinical genetic testing.

Rare Coding Variants Associated With Electrocardiographic Intervals Identify Monogenic Arrhythmia Susceptibility Genes: A Multi-Ancestry Analysis

BACKGROUND

Alterations in electrocardiographic (ECG) intervals are well-known markers for arrhythmia and sudden cardiac death (SCD) risk. While the genetics of arrhythmia syndromes have been studied, relations between electrocardiographic intervals and rare genetic variation at a population level are poorly understood.

METHODS

Using a discovery sample of 29 000 individuals with whole-genome sequencing from Trans-Omics in Precision Medicine and replication in nearly 100 000 with whole-exome sequencing from the UK Biobank and MyCode, we examined associations between low-frequency and rare coding variants with 5 routinely measured electrocardiographic traits (RR, P-wave, PR, and QRS intervals and corrected QT interval).

RESULTS

We found that rare variants associated with population-based electrocardiographic intervals identify established monogenic SCD genes (KCNQ1, KCNH2, and SCN5A), a controversial monogenic SCD gene (KCNE1), and novel genes (PAM and MFGE8) involved in cardiac conduction. Loss-of-function and pathogenic SCN5A variants, carried by 0.1% of individuals, were associated with a nearly 6-fold increased odds of the first-degree atrioventricular block (P=8.4×10^-5). Similar variants in KCNQ1 and KCNH2 (0.2% of individuals) were associated with a 23-fold increased odds of marked corrected QT interval prolongation (P=4×10^-25), a marker of SCD risk. Incomplete penetrance of such deleterious variation was common as over 70% of carriers had normal electrocardiographic intervals.

CONCLUSIONS

Our findings indicate that large-scale high-depth sequence data and electrocardiographic analysis identifies monogenic arrhythmia susceptibility genes and rare variants with large effects. Known pathogenic variation in conventional arrhythmia and SCD genes exhibited incomplete penetrance and accounted for only a small fraction of marked electrocardiographic interval prolongation.

Massive Pulmonary Embolism Causing Cardiac Arrest Managed with Systemic Thrombolytic Therapy: A Case Report

BACKGROUND Approximately 290 000 cases of in-hospital cardiac arrest occur annually, the majority of which are due to cardiac or respiratory causes. Cardiac arrest due to acute pulmonary embolism (PE) is associated with a 90% incidence of mortality and, if identified, it can be treated with systemic thrombolytics. Here, we describe a case in which the outcome for such an event was favorable. CASE REPORT A 66-year-old woman was admitted with multiple rib and left ankle fractures due to accidental trauma. Before undergoing orthopedic surgery, she experienced a cardiac arrest with pulseless electrical activity, which was witnessed. She had refractory hypoxia and hypotension following intubation and a brief initial return of spontaneous circulation (ROSC) before a second cardiac arrest. A 100-mg bolus dose of systemic thrombolytic therapy was promptly administered, with rapid achievement of sustained ROSC. The results of a subsequent electrocardiogram, echocardiogram, and computed tomography scan further supported the diagnosis of acute PE with right heart strain. Supportive care in the Intensive Care Unit resulted in full neurological recovery and she was discharged to a physical rehabilitation facility 12 days after her cardiac arrest. CONCLUSIONS Systemic thrombolytic therapy is beneficial for cardiac arrest due to acute PE.

Molecular Genetic Basis of Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic disease of the myocardium characterized by a hypertrophic left ventricle with a preserved or increased ejection fraction. Cardiac hypertrophy is often asymmetrical, which is associated with left ventricular outflow tract obstruction. Myocyte hypertrophy, disarray, and myocardial fibrosis constitute the histological features of HCM. HCM is a relatively benign disease but an important cause of sudden cardiac death in the young and heart failure in the elderly. Pathogenic variants (PVs) in genes encoding protein constituents of the sarcomeres are the main causes of HCM. PVs exhibit a gradient of effect sizes, as reflected in their penetrance and variable phenotypic expression of HCM. MYH7 and MYBPC3, encoding β-myosin heavy chain and myosin binding protein C, respectively, are the two most common causal genes and responsible for ≈40% of all HCM cases but a higher percentage of HCM in large families. PVs in genes encoding protein components of the thin filaments are responsible for ≈5% of the HCM cases. Whereas pathogenicity of the genetic variants in large families has been firmly established, ascertainment causality of the PVs in small families and sporadic cases is challenging. In the latter category, PVs are best considered as probabilistic determinants of HCM. Deciphering the genetic basis of HCM has enabled routine genetic testing and has partially elucidated the underpinning mechanism of HCM as increased number of the myosin molecules that are strongly bound to actin. The discoveries have led to the development of mavacamten that targets binding of the myosin molecule to actin filaments and imparts beneficial clinical effects. In the coming years, the yield of the genetic testing is expected to be improved and the so-called missing causal gene be identified. The advances are also expected to enable development of additional specific therapies and editing of the mutations in HCM.