Clinical Detection of LQTS Mutation Carriers
How do the updated criteria for the diagnosis of long QT syndrome (LQTS) compare with prior diagnostic criteria?
The authors scored cases of LQTS patients by using different Schwartz diagnostic criteria from 1993, 2006, and 2011. A cohort of 132 patients was examined; all presented with prolonged QT corrected for heart rate (QTc) intervals and/or abnormal clinical history, and underwent exercise stress testing. LQTS scores of ≥3.5 points by the 2006 and 2011 criteria were considered to indicate high probability of LQTS, as opposed to 4 points by the 1993 criteria. The 2011 criteria were updated by adding the evaluation of the recovery phase of exercise.
The 2011 criteria significantly increased the number of high probability patients (n = 62) compared to the 1993 criteria (n = 32) or the 2006 criteria (n = 36). The percentage of mutation carriers in those with an intermediate score, which was rather high, with the 1993 (53%) and 2006 criteria (53%), was greatly reduced with the 2011 criteria (15%). Among 54 mutation carriers, the 1993, 2006, and 2011 criteria identified high probability patients in 25 (46% sensitivity and 91% specificity), 27 (50% sensitivity and 88% specificity), and 48 (89% sensitivity and 82% specificity), respectively.
The authors concluded that the use of the 2011 criteria facilitates the diagnosis of LQTS by decreasing the number of false-negative results.
While the diagnosis of LQTS is predicated on the measurement of the QTc interval, approximately 20-25% of patients with LQTS confirmed by the presence of a LQTS gene mutation have a QTc in the normal range. Thus, diagnostic scoring, taking into account the age of the patient, medical and family history, symptoms, and QTc, has been used to determine the likelihood of LQTS. The newest ‘2011 criteria’ also include an evaluation of the recovery phase of exercise testing, which can unmask patients with occult LQTS, particularly LQT1. The results of the current study show that inclusion of the exercise test results can identify more silent gene mutation carriers as being at a high probability of LQTS. The implication is that patients in whom the diagnosis of LQTS is seriously contemplated, but not confirmed, should undergo an exercise test.
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