Evaluation of Prolonged QT Interval: Structural Heart Disease Mimicking Long QT Syndrome.
BACKGROUND
In about 20-25% of patients with congenital long QT syndrome (LQTS) a causative pathogenic mutation is not found. The aim of this study was to explore the prevalence of alternative cardiac diagnoses among patients exhibiting prolongation of QT interval with negative genetic testing for LQTS genes.


METHODS
We conducted a retrospective analysis of 239 consecutive patients who were evaluated in the inherited arrhythmia clinic at the Toronto General Hospital between July 2013 and December 2015 for possible LQTS. A detailed review of the patients' charts, electrocardiograms, and imaging was carried out.


RESULTS
The analysis included 56 gene-negative patients and 61 gene-positive patients. Of the gene-negative group, 25% had structural heart disease compared to only 1.6% of gene-positive patients (P < 0.001). Structural heart disease was more likely if only one abnormal QTc parameter was found in the course of the evaluation (35.2% vs 9.1%, P = 0.01). The most common structural cardiac pathology was bileaflet mitral valve prolapse (8.9%). No gene-positive patient had episodes of nonsustained ventricular tachycardia, compared to seven of the gene-negative patients (0% vs 12.5%, P = 0.005).


CONCLUSIONS
Structural pathology was detected in a quarter of gene-negative patients evaluated for possible LQTS. Hence, cardiac imaging and Holter monitoring should be strongly encouraged to rule out structural heart disease in this population.
Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
Adaya
A
Weissler-Snir
Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
Michael H
MH
Gollob
Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
Vijay
V
Chauhan
Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
Melanie
M
Care
Division of Cardiology, Peter Munk Cardiac Centre, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada.
Danna A
DA
Spears
D000328:Adult; D057791:Cardiac Imaging Techniques / Q000379:methods*; D009202:Cardiomyopathies / Q000175:diagnosis* / Q000235:genetics; D003937:Diagnosis, Differential; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005820:Genetic Testing; D006801:Humans; D008133:Long QT Syndrome / Q000000981:diagnostic imaging* / Q000235:genetics*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
gene negative; long QT syndrome; prolonged QT interval; structural heart disease