Sustained Ventricular Tachycardia Presenting As Gastrointestinal (GI) Symptoms.

Ventricular arrhythmias (VAs) are among the most common cardiac rhythms seen among patients. Patients presenting with frequent, sustained ventricular tachycardia (VT) pose a dilemma for clinicians due to the constant risk of sudden cardiovascular compromise. Ventricular tachycardia, which is commonly seen in patients with defects in cardiac anatomy, has been associated with an increased risk of sudden death. A previous myocardial scar from a previous myocardial infarction remains the most common cause of sustained monomorphic VT (SMVT) in patients with structural cardiac disease. Studies have shown that implantable cardioverter-defibrillators (ICDs) can be used for primary prevention in patients with ischemic or nonischemic cardiomyopathy whose ejection fraction remains below 35% despite guideline-directed medical therapy. It can also be used for secondary prevention of sudden cardiac death in patients who have had a VT or ventricular fibrillation (VF). Identifying individuals at risk for developing deleterious VTs who will benefit from ICD placement for prevention has been the objective of many large studies in recent years. We present a case of clinical importance involving the use of ICD in the primary prevention of mortality from sustained ventricular arrhythmias.

Genomic organization, alternative splicing, and expression of human and mouse N-RAP, a nebulin-related LIM protein of striated muscle.

Linkage analysis identifies 10q24-26 as a disease locus for dilated cardiomyopathy (DCM), a region including the N-RAP gene. N-RAP is a nebulin-like LIM protein that may mediate force transmission and myofibril assembly in cardiomyocytes. We describe the sequence, genomic structure, and expression of human N-RAP, as well as an initial screen to determine whether N-RAP mutations cause cardiomyopathy. Human expressed sequence tag databases were searched with the published 3,528-bp mouse N-RAP open reading frame (ORF). Putative cDNA sequences were interrogated by direct sequencing from cardiac and skeletal muscle RNA. We identified two human N-RAP isoforms with ORFs of 5,085 bp (isoform C) and 5,190 bp (isoform S), encoding products of 193-197 kDa. Genomic database searches localize N-RAP to human chromosome 10q25.3 and match isoforms C and S to 41 and 42 exons. Only isoform C is detected in human cardiac RNA; in skeletal muscle, approximately 10% is isoform C and approximately 90% is isoform S. We investigated apparent differences between human N-RAP cDNA and mouse sequences. Two mouse N-RAP isoforms with ORFs of 5,079 and 5,184 bp were identified with approximately 85% similarity to human isoforms; published mouse sequences include cloning artifacts truncating the ORF. Murine and human isoforms have similar gene structure, tissue specificity, and size. N-RAP is especially conserved within its nebulin-like and LIM domains. We expressed both N-RAP isoforms and the previously described truncated N-RAP in embryonic chick cardiomyocytes. All constructs targeted to myofibril precursors and the cell periphery, and inhibited myofibril assembly. Several human N-RAP polymorphisms were detected, but none were unique to cardiomyopathy patients. N-RAP is highly conserved and exclusively expressed in cardiac and skeletal muscle. Genetic abnormalities remain excellent candidate causes for cardiac and skeletal myopathies.