Faculty Bibliography

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disease associated with a high risk of sudden cardiac death. Among other factors, physical exercise has been clearly identified as a strong determinant of phenotypic expression of the disease, arrhythmia risk, and disease progression. Because of this, current guidelines advise that individuals with ARVC should not participate in competitive or frequent high-intensity endurance exercise. Exercise-induced electrical and morphological para-physiological remodelling (the so-called 'athlete's heart') may mimic several of the classic features of ARVC. Therefore, the current International Task Force Criteria for disease diagnosis may not perform as well in athletes. Clear adjudication between the two conditions is often a real challenge, with false positives, that may lead to unnecessary treatments, and false negatives, which may leave patients unprotected, both of which are equally inacceptable. This review aims to summarize the molecular interactions caused by physical activity in inducing cardiac structural alterations, and the impact of sports on arrhythmia occurrence and other clinical consequences in patients with ARVC, and help the physicians in setting the two conditions apart.

Bileaflet mitral valve prolapse (Bi-MVP) is associated with increased risk for cardiac arrest. We describe a patient who presented after a cardiac arrest with Bi-MVP and variants in Lamin A/C (LMNA) and the sodium channel alpha-subunit 5a (SCN5A). Genetic variants may be the culprit for arrhythmogenesis in Bi-MVP patients. (Level of Difficulty: Intermediate.).

Implantable loop recorders (ILRs) can be a valuable tool in monitoring patients with inherited arrhythmia. This paper reports on a family with long QT syndrome (type 2 [LQT2]) in which a pseudopolymorphic wide complex tachycardia detected by ILR was ultimately diagnosed as a supraventricular aberrant rhythm, facilitated by noncompliance with beta-blocker therapy. (Level of Difficulty: Intermediate.).

Plakophilin-2 (PKP2) is classically defined as a component of the desmosome. Besides its role in cell-cell adhesion, PKP2 can modulate transcription through intracellular signals initiated at the site of cell-cell contact. Mutations in PKP2 associate with arrhythmogenic right ventricular cardiomyopathy (ARVC). Recent data demonstrate that inflammation plays a key role in disease progression; other results show an abundance of anti-heart antibodies in patients with confirmed diagnosis of ARVC. Here, we test the hypothesis that, in adult cardiac myocytes, PKP2 transcript abundance is endogenously linked to the abundance of transcripts participating in the inflammatory/immune response. Cardiac-specific, tamoxifen (TAM)-activated PKP2-knockout mice (PKP2cKO) were crossed with a RiboTag line to allow characterization of the ribosome-resident transcriptome of cardiomyocytes after PKP2 knockdown. Data were combined with informatics analysis of human cardiac transcriptome using GTEx. Separately, the presence of non-myocyte cells at the time of analysis was assessed by imaging methods. We identified a large number of transcripts upregulated consequent to PKP2 deficiency in myocytes, inversely correlated with PKP2 abundance in human transcriptomes, and part of functional pathways associated with inflammatory/immune responses. Our data support the concept that PKP2 is transcriptionally linked, in cardiac myocytes, to genes coding for host-response molecules even in the absence of exogenous triggers. Targeted anti-inflammatory therapy may be effective in ARVC.

Background: Plakophilin-2 (PKP2) is classically defined as a protein of the desmosome, an intercellular adhesion structure that also acts as a signaling hub to maintain structural and electrical homeostasis. Mutations in PKP2 associate with most cases of gene-positive arrhythmogenic right ventricular cardiomyopathy (ARVC). A better understanding of PKP2 cardiac biology can help elucidate the mechanisms underlying arrhythmic and cardiomyopathic events that occur consequent to its mutation. Here we sought to captureearly molecular/cellular events that can act as nascent substrates for subsequent arrhythmic/cardiomyopathic phenotypes.
Method(s): We used multiple quantitative imaging modalities, as well as biochemical and high-resolution mass spectrometry methods to study the functional/structural properties of cells/tissues derived from cardiomyocytespecific, tamoxifen-activated, PKP2 knockout mice ("PKP2cKO"). Studies were carried out 14 days post-tamoxifen injection, a time point preceding an overt electrical or structural phenotype.Myocytes from right or left ventricular free wall were studied separately, to detect functional/structural asymmetries.
Result(s): Most properties of PKP2cKO left ventricular (LV) myocytes were not different from control; in contrast, PKP2cKO right ventricular (RV) myocytes showed increased amplitude and duration of Ca2+transients, increased frequency of spontaneous Ca2+release events, increased [Ca2+] in the cytoplasm and sarcoplasmic reticulum compartments, and dynamic Ca2+accumulation in mitochondria. In addition, RyR2 in RV presented enhanced sensitivity to Ca2+and preferential phosphorylation in a domain known to modulate Ca2+gating. RNAseq at 14 days post-TAM showed no relevant difference in transcript abundance between RV and LV, neither in control nor in PKP2cKO cells, suggesting that in the earliest stage, [Ca2+]i dysfunction is not transcriptional. Rather, we found an RV-predominant increase in membrane permeability that can permit Ca2+entry into the cell. Cx43 ablation mitigated the increase in membrane permeability, the accumulation of cytoplasmic Ca2+and the early stages of RV dysfunction.
Conclusion(s): Loss of PKP2 creates an RV-predominant arrhythmogenic substrate (Ca2+ dysregulation) that precedes the cardiomyopathy and that is, at least in part, mediated by a Cx43-dependent membrane conduit. Given that asymmetric Ca2+ dysregulation precedes the cardiomyopathic stage, we speculate that abnormal Ca2+ handling in RV myocytes can be a trigger for gross structural changes observed at a later stage

BACKGROUND:Plakophilin-2 (PKP2) is classically defined as a desmosomal protein. Mutations in PKP2 associate with most cases of gene-positive arrhythmogenic right ventricular cardiomyopathy (ARVC). A better understanding of PKP2 cardiac biology can help elucidate the mechanisms underlying arrhythmic and cardiomyopathic events consequent to PKP2 deficiency. Here, we sought to capture early molecular/cellular events that can act as nascent arrhythmic/cardiomyopathic substrates. METHODS:We used multiple imaging, biochemical and high-resolution mass spectrometry methods to study functional/structural properties of cells/tissues derived from cardiomyocyte-specific, tamoxifen-activated, PKP2 knockout mice ("PKP2cKO") 14 days post-tamoxifen (post-TAM) injection, a time point preceding overt electrical or structural phenotypes. Myocytes from right or left ventricular free wall were studied separately. RESULTS:homeostasis. Similarly, PKC inhibition normalized spark frequency at comparable SR load levels. CONCLUSIONS:handling in RV myocytes can be a trigger for gross structural changes observed at a later stage.

AIMS/OBJECTIVE:Calmodulinopathies are rare life-threatening arrhythmia syndromes which affect mostly young individuals and are, caused by mutations in any of the three genes (CALM 1-3) that encode identical calmodulin proteins. We established the International Calmodulinopathy Registry (ICalmR) to understand the natural history, clinical features, and response to therapy of patients with a CALM-mediated arrhythmia syndrome. METHODS AND RESULTS/RESULTS:A dedicated Case Report File was created to collect demographic, clinical, and genetic information. ICalmR has enrolled 74 subjects, with a variant in the CALM1 (n = 36), CALM2 (n = 23), or CALM3 (n = 15) genes. Sixty-four (86.5%) were symptomatic and the 10-year cumulative mortality was 27%. The two prevalent phenotypes are long QT syndrome (LQTS; CALM-LQTS, n = 36, 49%) and catecholaminergic polymorphic ventricular tachycardia (CPVT; CALM-CPVT, n = 21, 28%). CALM-LQTS patients have extremely prolonged QTc intervals (594 ± 73 ms), high prevalence (78%) of life-threatening arrhythmias with median age at onset of 1.5 years [interquartile range (IQR) 0.1-5.5 years] and poor response to therapies. Most electrocardiograms (ECGs) show late onset peaked T waves. All CALM-CPVT patients were symptomatic with median age of onset of 6.0 years (IQR 3.0-8.5 years). Basal ECG frequently shows prominent U waves. Other CALM-related phenotypes are idiopathic ventricular fibrillation (IVF, n = 7), sudden unexplained death (SUD, n = 4), overlapping features of CPVT/LQTS (n = 3), and predominant neurological phenotype (n = 1). Cardiac structural abnormalities and neurological features were present in 18 and 13 patients, respectively. CONCLUSION/CONCLUSIONS:Calmodulinopathies are largely characterized by adrenergically-induced life-threatening arrhythmias. Available therapies are disquietingly insufficient, especially in CALM-LQTS. Combination therapy with drugs, sympathectomy, and devices should be considered.