Torsade De Pointes
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Objectives
The objectives of this case study are to evaluate the cause of death for a female patient that presented to the ER with ventricular tachycardia, of which elevated to ventricular fibrillation and was unsuccessfully resuscitated. Furthermore, what genetic presupposition to development of VT did she have, and how was this augmented by the influence of Seldane ® (active ingredient terfenadine), an over the counter anti-histamine allergy season remedy.
Clinical History
During spring time of 1998, a typically healthy 43 year old deaf woman presented in the ER with cardiac arrhythmia. Electrocardiogram (ECG) analysis showed a broad QRS segment, suggesting sustained ventricular tachycardia (VT). Due to the ECG analysis, chemical cardioconversion by lidocaine administration was attempted (a 100 mg IV was rapidly run for 2 minutes as standard initial procedure); however, rapid onset of ventricular fibrillation occurred. Direct current defibrillation was employed with a range of 200-300 joules, but unfortunately was unsuccessful. Before a second attempt of defibrillation could be administered, the woman presented with syncope. CPR was attempted however was unsuccessful; briefly after was pronounced dead due to sudden cardiac death (SCD).
Investigations
Blood samples showed sodium (Na+), potassium (K+), and calcium (Ca2+) imbalances, and high content of over the counter antihistamine active ingredient terfenadine. After overview of the patient’s medical history, it was confirmed that her deafness was of congenital nature (specifically neurosensorial). Understanding that this feature is often linked to congenital long QT syndromes, genetic analysis was performed. Analysis found a point mutation in the KCNQ1 and KCNE1 genes (found on chromosome 11), of which she was homozygous recessive.
Discussion: Clinico-pathological Correlations
The genetic findings on chromosome 11 specifically regarding genes KCNQ1 and KCNE1 definitively confirm that the women suffered from Jervell-Lange-Nielsen syndrome (JLNS). JLNS is a congenital long QT syndrome with autosomal recessive associated deafness (Berkow, 492). The alterations in genes KCNQ1 and KCNE1 in most cases prolong the action potential time span (see Figure 1.0) by increasing inward depolarizing currents or decreasing outward repolarising currents during the plateau phase (Figure 2.0). Specifically for JLNS, the slow acting potassium transporter IKs shows a decrease in outward transportation of potassium during the repolarising phase of the cardiac action potential cycle. This decrease in transporter efficacy is directly related to the mutations in genes KCNQ1 and KCNE1 (Hugues A. et al.). Overall, this genetic predisposition to the development of ventricular arrhythmia due to the long QT repolarisation is termed Torsade de Pointes; this is because although clinically the ECG looks similar to that of ventricular tachycardia, in this case the ECG shows a continuously changing QRS vector that is often sparked by the generation of one or two extrasystole occurances(Figure 3.0) (Berkow 491). Risk factors for Torsade de Pointes include female gender, heart disease, hypokalemia,