Catecholaminergic polymorphic ventricular tachycardia: successful emergency treatment with intravenous propranolol

Pediatric Catecholaminergic Polymorphic Ventricular Tachycardia: A Translational Perspective for the Clinician-Scientist

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare and potentially lethal inherited arrhythmia disease characterized by exercise or emotion-induced bidirectional or polymorphic ventricular tachyarrhythmias. The median age of disease onset is reported to be approximately 10 years of age. The majority of CPVT patients have pathogenic variants in the gene encoding the cardiac ryanodine receptor, or calsequestrin 2. These lead to mishandling of calcium in cardiomyocytes resulting in after-depolarizations, and ventricular arrhythmias. Disease severity is particularly pronounced in younger individuals who usually present with cardiac arrest and arrhythmic syncope. Risk stratification is imprecise and long-term prognosis on therapy is unknown despite decades of research focused on pediatric CPVT populations. The purpose of this review is to summarize contemporary data on pediatric CPVT, highlight knowledge gaps and present future research directions for the clinician-scientist to address.

Utility of a pediatric observation unit for the management of children admitted to the emergency department

BACKGROUND

Observation Units (OU), as part of emergency department (ED), are areas reserved for short-term treatment or observation of patients with selected diagnoses to determine the need for hospitalization or home referral.

METHODS

In this retrospective cohort study, we analyzed similarities and differences of children admitted to the pediatric ED of the Fondazione Policlinico Universitario A. Gemelli IRCCS hospital in the first 2 years of OU activity, analyzing general patient characteristics, access modalities, diagnosis, triage, laboratory and instrumental examinations, specialist visits, outcome of OU admission and average time spent in OU. Furthermore, we compared total numbers and type of hospitalization of the first 2 years of OU activity with those of previous 2 years.

RESULTS

The most frequent diagnoses were abdominal pain, minor head injury without loss of consciousness, vomiting, epilepsy and acute bronchiolitis. The most performed laboratory examinations were blood count. The most commonly performed instrumental examination was abdominal ultrasound. Neurological counseling was the most commonly requested. Average time spent in OU was 13 h in 2016 and 14.1 h in 2017. Most OU admissions did not last longer than 24 h (90.5% in 2016 and 89.5% in 2017). In the years 2014-2015, 13.4% of pediatric patients accessing the ED were hospitalized, versus 9.9% the years 2016-2017 reducing pediatric hospital admissions by 3.6% (p <  0.001).

CONCLUSIONS

This study demonstrate that OU is a valid alternative to ordinary wards for specific pathologies. In accordance with the literature, our study showed that, in the first 2 years of the OU activity, admissions to hospital ward decreased compared with the previous 2 years with an increase of complex patients.

Themes and variations in ER/SR calcium release channels: structure and function

Calcium (Ca(2+)) release from reticular stores is a vital regulatory signal in eukaryotes. Recent structural data on large NH(2)-terminal regions of IP(3)Rs and RyRs and their tetrameric arrangement in the full-length context reveal striking mechanistic similarities in Ca(2+) release channel function. A common ancestor found in unicellular genomes underscores the fundamentality of these elements to Ca(2+) release channels.

[Catecholaminergic polymorphic ventricular tachycardia]

Catecholaminergic polymorphic ventricular tachycardia (PCVT) is a rare, congenital ventricular tachyarrhythmia which occurs in the setting of adrenergic activation. It potentially leads to syncope and/or sudden cardiac death (SCD). PCVT represents one of the most dangerous congenital ion channel diseases. Mutations of the ryanodine receptor gene (RYR2), the calsequestrin gene (CASQ2), and the triadin gene (TRDN) have been identified as an underlying correlate. β-Blockers are employed as therapy and are sometimes combined with class IC antiarrhythmic drugs, or calcium antagonists of the verapamil type. ICD implantation is recommended in case of persisting syncope in the presence of β-blocker therapy or survived SCD. Left thoracic sympathectomy represents a subsidiary interventional therapy for individual cases. In addition, modifications of the patient's lifestyle including avoidance of physical stress and heart rates> 120/min are recommended.

Primary cardiac arrest following sport or exertion in children presenting to an emergency department: chest compressions and early defibrillation can save lives, but is intravenous epinephrine always appropriate?

OBJECTIVES

The objective of this study was to describe the characteristics and outcome of pediatric patients presenting to an emergency department (ED) following out-of-hospital primary cardiac arrest (OHPCA), to determine if long-term survival is influenced by specific resuscitation interventions.

METHODS

This was a prospective observational study of cases of OHPCA during sport or exertion in young patients presenting to an ED over a 5-year period. Cases were identified from a resuscitation database, which documented patient demographics, nature of event, emergency treatment, response times, and clinical progress. These data were analyzed to determine outcomes.

RESULTS

Nine children were identified who presented following OHPCA during the study period. The mean age was 10.7 (±4.2) years. All were subsequently diagnosed with an underlying primary cardiac disorder. Six patients (66.6%) survived to make a full recovery. All patients who survived had received early chest compressions (within 5 minutes) and early defibrillation (within 10 minutes). The initial cardiac arrest rhythm in all survivors had been an electrically cardiovertable rhythm. Five (83%) of the 6 survivors did not receive epinephrine during resuscitation.

CONCLUSIONS

The importance of early chest compressions and defibrillation in collapsed young athletes is highlighted in this report. These interventions can result in full long-term neurological recovery. Use of epinephrine in these patients may be dangerous. We suggest that special consideration should be given to this subgroup of patients in the development of future resuscitation guidelines.

Flecainide prevents catecholaminergic polymorphic ventricular tachycardia in mice and humans

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited arrhythmia syndrome in which drug therapy is often ineffective. We discovered that flecainide prevents arrhythmias in a mouse model of CPVT by inhibiting cardiac ryanodine receptor-mediated Ca(2+) release and thereby directly targeting the underlying molecular defect. Flecainide completely prevented CPVT in two human subjects who had remained highly symptomatic on conventional drug therapy, indicating that this currently available drug is a promising mechanism-based therapy for CPVT.

Exercise-induced polymorphic ventricular tachycardia in adults without structural heart disease

Patients with catecholaminergic polymorphic ventricular tachycardia present at a young age with exercise-induced ventricular arrhythmias (VAs) and may have a positive family history. We describe 8 patients who presented with exercise-induced symptoms as adults, have a negative family history, and responded to beta-blocker therapy. The study evaluated exercise treadmill electrocardiographic data from patients referred for exercise-induced VA. Inclusion criteria consisted of development of bidirectional, pleomorphic, or polymorphic ventricular tachycardia with exercise, adult age at first onset, negative family history, and no evidence of structural heart disease. We correlated VA configurations with respect to heart rate before and after beta-blocker therapy. Patients displayed a pattern of increasing ventricular complexity with increasing heart rate. The appropriate beta blocker (n = 7) or calcium channel blocker (n = 1) was defined as the dose that resulted in control of symptoms. Three patients showed suppression of VA with sinus tachycardia at peak heart rate. Six patients had decreased VA defined as absence of higher complexity arrhythmias. With drug therapy, average heart rate associated with premature ventricular complex couplets/triplets increased, whereas duration and complexity of premature ventricular complexes decreased. One patient had an automatic implantable cardiac defibrillator placed but has had no discharges from the device since starting the appropriate beta blocker. In conclusion, these patients appear to respond well to beta-blocker or calcium channel blocker therapy with decreased ectopic complexity and an increased heart rate threshold for inducing VA.

Stabilization of cardiac ryanodine receptor prevents intracellular calcium leak and arrhythmias

Catecholaminergic polymorphic ventricular tachycardia is a form of exercise-induced sudden cardiac death that has been linked to mutations in the cardiac Ca2+ release channel/ryanodine receptor (RyR2) located on the sarcoplasmic reticulum (SR). We have shown that catecholaminergic polymorphic ventricular tachycardia-linked RyR2 mutations significantly decrease the binding affinity for calstabin-2 (FKBP12.6), a subunit that stabilizes the closed state of the channel. We have proposed that RyR2-mediated diastolic SR Ca2+ leak triggers ventricular tachycardia (VT) and sudden cardiac death. In calstabin-2-deficient mice, we have now documented diastolic SR Ca2+ leak, monophasic action potential alternans, and bidirectional VT. Calstabin-deficient cardiomyocytes exhibited SR Ca2+ leak-induced aberrant transient inward currents in diastole consistent with delayed after-depolarizations. The 1,4-benzothiazepine JTV519, which increases the binding affinity of calstabin-2 for RyR2, inhibited the diastolic SR Ca2+ leak, monophasic action potential alternans and triggered arrhythmias. Our data suggest that calstabin-2 deficiency is as a critical mediator of triggers that initiate cardiac arrhythmias.

Experimental therapy of genetic arrhythmias: disease-specific pharmacology

The integration between molecular biology and clinical practice requires the achievement of fundamental steps to link basic science to diagnosis and management of patients. In the last decade, the study of genetic bases of human diseases has achieved several milestones, and it is now possible to apply the knowledge that stems from the identification of the genetic substrate of diseases to clinical practice. The first step along the process of linking molecular biology to clinical medicine is the identification of the genetic bases of inherited diseases. After this important goal is achieved, it becomes possible to extend research to understand the functional impairments of mutant protein(s) and to link them to clinical manifestations (genotype-phenotype correlation). In genetically heterogeneous diseases, it may be possible to identify locus-specific risk stratification and management algorithms. Finally, the most ambitious step in the study of genetic disease is to discover a novel pharmacological therapy targeted at correcting the inborn defect (locus-specific therapy) or even to "cure" the DNA abnormality by replacing the defective gene with gene therapy. At present, this curative goal has been successful only for very few diseases. In the field of inherited arrhythmogenic diseases, several genes have been discovered, and genetics is now emerging as a source of information contributing not only to a better diagnosis but also to risk stratification and management of patients. The functional characterization of mutant proteins has opened new perspectives about the possibility of performing gene-specific or mutation-specific therapy. In this chapter, we will briefly summarize the genetic bases of inherited arrhythmogenic conditions and we will point out how the information derived from molecular genetics has influenced the "optimal use of traditional therapies" and has paved the way to the development of gene-specific therapy.

Catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (VT) is a rare arrhythmogenic disease characterized by exercise- or stress-induced ventricular tachyarrhythmias, syncope, or sudden death, usually in the pediatric age group. Familial occurrence has been noted in about 30% of cases. Inheritance can be autosomal dominant or recessive, usually with high penetrance. The causative genes have been mapped to chromosome 1. Mutations of the cardiac ryanodine receptor gene (RyR2) have been identified in autosomal dominant pedigrees, while calsequestrin gene (CASQ2) mutations are seen in recessive cases. Ankyrin-B mutations may also be implicated in catecholaminergic polymorphic VT: mutations in this gene were previously linked to the long-QT 4 phenotype. Ventricular ectopy, bidirectional VT, and polymorphic VT occur in a predictable and progressive manner with increasing heart rate during exercise or isoproterenol infusion. Estimated mortality of untreated cases ranges from 30% to 50% before the age of 20-30 years according to family studies. Although beta-blocker therapy was considered to be effective in preventing clinical recurrence in the initial series, recent data show low efficacy. As there is a chance for sudden cardiac death if even a single dose of beta-blocker is missed, there is a trend toward implantation of defibrillators in more and more patients.