The conduction system findings in sudden cardiac death

Phytanic acid accumulation is associated with conduction delay and sudden cardiac death in sterol carrier protein-2/sterol carrier protein-x deficient mice

INTRODUCTION

The sterol carrier protein-2 gene encodes two functionally distinct proteins: sterol carrier protein-2 (SCP2, a peroxisomal lipid carrier) and sterol carrier protein-x (SCPx, a peroxisomal thiolase known as peroxisomal thiolase-2), which is involved in peroxisomal metabolism of bile acids and branched-chain fatty acids. We show in this study that mice deficient in SCP2 and SCPx (SCP2null) develop a cardiac phenotype leading to a high sudden cardiac death rate if mice are maintained on diets enriched for phytol (a metabolic precursor of branched-chain fatty acids).

METHODS AND RESULTS

In 210 surface and 305 telemetric ECGs recorded in wild-type (C57BL/6; wt; n = 40) and SCP2 null mice (n = 40), no difference was observed at baseline. However, on diet, cycle lengths were prolonged in SCP2 null mice (262.9 +/- 190 vs 146.3 +/- 43 msec), AV conduction was prolonged (58.3 +/- 17 vs 42.6 +/- 4 ms), and QRS complexes were wider (19.1 +/- 5 vs 14.0 +/- 4 ms). In 11 gene-targeted Langendorff-perfused hearts isolated from SCP2 null mice after dietary challenge, complete AV blocks (n = 5/11) or impaired AV conduction (Wenckebach point 132 +/- 27 vs 92 +/- 10 msec; P < 0.05) could be confirmed. Monophasic action potentials were not different between the two genotypes. Left ventricular function studied by echocardiography was similar in both strains. Phytanic acid but not pristanic acid accumulated in the phospholipid fraction of myocardial membranes isolated from SCP2 null mice.

CONCLUSION

Accumulation of phytanic acid in myocardial phospholipid membranes is associated with bradycardia and impaired AV nodal and intraventricular impulse conduction, which could provide an explanation for sudden cardiac death in this model.

Sudden cardiac death in a 5-year-old girl associated with parvovirus B19 infection

We report on a 5-year-old girl who suddenly collapsed and died while dancing at a family party. Histological examination of the heart including the cardiac conduction system revealed lymphocytic infiltrations of the sinu-atrial node and perivascular infiltration in the atrio-ventricular region. Additionally, foci of mononuclear infiltrates were observed in the myocardium. Consequently, myocarditis was diagnosed as cause of death. The child also had lymphocytic conjunctivis, parotitis and tracheitis. Evaluation of infections by means of nested polymerase chain reaction revealed parvovirus B19 DNA (PVB19) in tissue samples of the trachea.

Evaluation of a simplified method of the conduction system analysis in 110 forensic cases

A simplified method of the His bundle analysis is evaluated by the study of 110 forensic cases. The atrioventricular node or its part were observed in 96 cases (87.3%), penetrating bundle in 92 cases (83.6%), branching and left bundles branch in 109 cases (99.1%) and right bundle branch in 73 cases (66.4%). The changes such as fibrosis and fatty infiltration show statistically significant differences (P<0.01) between progressive age groups confirming their degenerative and age-related nature. The study included as well nine cases of sudden unexpected death and two cases of sudden infant death syndrome (SIDS), for which the autopsy with histological examination and toxicological analysis resulted negative. For nine of these cases, pathological lesions were found which can even explain the fatal issue. Moreover, in the cases with known cause of death, potentially lethal changes were noticed. This simple, low cost technique could be proposed to forensic pathologists as easy to fit into the routine processing of autopsy material, allowing the detection of major abnormalities with minimal effort. The authors also consider the difficulties related to the interpretation of the pathological findings in the conduction system.

Sudden cardiac death associated with hypoplasia of the coronary arteries and conduction system alteration

We present a case of sudden cardiac death in a 24-year-old woman with evidence of hypoplasia of the left anterior descending (LAD) and posterior descending (PDA) coronary arteries. These vessels averaged 0.7 mm in internal diameter combined, in contrast to an average of 2.4 mm in control coronary arteries (p < 0.001). The myocardium exhibited areas of acute and chronic ischemic change. Also, the cardiac conduction system (CCS) had diffuse cellular enlargement, believed to be secondary to ischemia. The cells of the sinoatrial node (SAN) and the Purkinje cells of the proximal right bundle branch (RBB) averaged 28.5 and 25.6 microns, respectively. These were significantly larger than the SAN cells (21.6 microns, p = 0.002) and larger than the Purkinje cells (15.9 microns, p = 0.012) of control cases. We report that hypoplastic coronary artery disease is a cause of sudden death, is associated with varying degrees of ischemic change in the heart, and can be associated with condition system alteration.