Ritme idioventricular accelerat transitori en un nounat afectat d’acidèmia metilmalònica / Ritmo idioventricular acelerado en un neonato afecto de acidemia metilmalónica / Transient accelerated idioventricular rhythm in a newborn with methylmalonic academia

Introducció: el ritme accelerat idioventricular (RIVA) és una disrítmia originada a nivell dels feixos de His, de les fibres de Purkinje o dels miòcits ventriculars, molt rara en infants i nadons. Cas clínic: es presenta el cas d'un nounat a terme amb la presència de RIVA els primers dies de vida, sense repercus-sió hemodinàmica, i que s'autolimita als dos mesos d'edat. Posteriorment es va diagnosticar d'acidèmia metilmalònica tipus mut0, i es va iniciar el tractament amb dieta específica, carnitina i vitamina B12, amb bon control metabòlic. En el seguiment presenta extrasístoles ventriculars aïllades i un desenvolupament físic i psicomotor correctes. Comentaris: la identificació d'aquesta disrítmia pot ser difícil i és de gran transcendència, ja que planteja el diagnòstic diferencial principalment amb la taquicàrdia ventricular. El seu pronòstic generalment és benigne i tendeix a la resolució espontània; per tant, els fàrmacs antiarítmics no estan indicats. La coexistència de RIVA i acidèmia metilmalònica en un mateix pacient no ha estat descrita fins al moment

Introducción. El ritmo acelerado idioventricular (RIVA) es una disritmia originada a nivel de los haces de His, de las fibras de Purkinje o de los miocitos ventriculares, muy rara en niños y neonatos. Caso clínico. Se presenta el caso de un recién nacido a término con la presencia de RIVA los primeros días de vida, sin repercusión hemodinámica, y que se autolimita a los dos meses de edad. Posteriormente se diagnosticó de acidemia metilmalónica tipo mut0, y se inició el tratamiento con dieta específica, carnitina y vitamina B12, con buen control metabólico. En el seguimiento presenta extrasístoles ventriculares aisladas y un desarrollo físico y psicomotor correctos. Comentarios. La identificación de esta disritmia puede ser difícil y es de gran trascendencia, puesto que plantea el diagnóstico diferencial principalmente con la taquicardia ventricular. Su pronostico es, generalmente, benigno y tiende a la resolución espontánea; por tanto, los fármacos antiarrítmicos no están indicados. La coexistencia de RIVA y acidemia metilmalónica no ha sido descrita hasta el momento en un mismo paciente (AU)

Introduction. The accelerated idioventricular rhythm (AIVR) is a very rare pediatric dysrhythmia originated in the bundles of His, Purkinje fibers, or ventricular myocytes. Case report. A term newborn presented with AIVR in the first days of life; he was hemodynamically stable, and the arrhythmia resolved by two months of age. The infant was subsequently diagnosed with mut0 methylmalonic acidemia, and was started on specific diet, carnitine, and vitamin B12, with good response. On follow-up, the infant was found to have isolated ventricular extrasystoles and normal physical and psychomotor development. Comments. The identification of this dysrhythmia can be difficult; its prompt recognition is critical due to its differential diagnosis with ventricular tachycardia. The prognosis is usually benign, with spontaneous resolution in most cases; thus, antiarrhythmic agents are not indicated. The coexistence of AIVR and methylmalonic academia has not been previously described (AU)

Purkinje fiber dysplasia (histiocytoid cardiomyopathy) with ventricular noncompaction in a savannah kitten.

In a 2-month-old female savannah kitten that died unexpectedly, the pathologic findings of significance were restricted to the heart and included abnormal Purkinje fibers and biventricular myocardial trabeculation or noncompaction. The Purkinje fibers were large, angular, and tightly packed. They contained few disorganized myofibrils among a rarified cytoplasm. The fibers were distinct from adjacent myocytes and were immunohistochemically positive for desmin, muscle actin, myoglobin, sarcomeric actin, and chromogranin A. These findings are identical to those that occur in children with histiocytoid cardiomyopathy, a fatal genetic mitochondrial disorder of Purkinje fibers. Ventricular noncompaction likely has a multifactoral cause that results from fetal arrest of ventricular organizational development that might occur in conjunction with, or independent of, histiocytoid cardiomyopathy.

Nkx2.5 cell-autonomous gene function is required for the postnatal formation of the peripheral ventricular conduction system.

The ventricular conduction system is responsible for rapid propagation of electrical activity to coordinate ventricular contraction. To investigate the role of the transcription factor Nkx2.5 in the morphogenesis of the ventricular conduction system, we crossed Nkx2.5(+/-) mice with Cx40(eGFP/+) mice in which eGFP expression permits visualization of the His-Purkinje conduction system. Major anatomical and functional disturbances were detected in the His-Purkinje system of adult Nkx2.5(+/-)/Cx40(eGFP/+) mice, including hypoplasia of eGFP-positive Purkinje fibers and the disorganization of the Purkinje fiber network in the ventricular apex. Although the action potential properties of the individual eGFP-positive cells were normal, the deficiency of Purkinje fibers in Nkx2.5 haploinsufficient mice was associated with abnormalities of ventricular electrical activation, including slowed and decremented conduction along the left bundle branch. During embryonic development, eGFP expression in the ventricular trabeculae of Nkx2.5(+/-) hearts was qualitatively normal, with a measurable deficiency in eGFP-positive cells being observed only after birth. Chimeric analyses showed that maximal Nkx2.5 levels are required cell-autonomously. Reduced Nkx2.5 levels are associated with a delay in cell cycle withdrawal in surrounding GFP-negative myocytes. Our results suggest that the formation of the peripheral conduction system is time- and dose-dependent on the transcription factor Nkx2.5 that is cell-autonomously required for the postnatal differentiation of Purkinje fibers.