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Recovery phase of stress test revealed most common long QT syndrome type
Horner JM. Heart Rhythm. 2011;8:1698-1704.
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Researchers have reported the strong diagnostic ability of treadmill exercise stress testing to uncover long QT syndrome in patients. New data show that the recovery phase displays significant and maladaptive changes in the QTc, unveiling the most common long QT syndrome type, LQT1.
Between 1998 and 2008, patients with LQT1 (n=82), LQT2 (n=55), LQT3 (n=18) and a genotype-negative control group (n=88) underwent treadmill stress testing. Before testing, patients completed a 3-minute pretest rest period: 1 minute sitting, 1 minute supine and 1 minute standing, followed by a 6-minute recovery period after reaching peak exercise. Researchers calculated QTc at rest, peak exercise and after 1 to 5 minutes of recovery.
Patients were distinguished with either manifest or concealed LQT1 from all other subsets with either an absolute QTc of 460 ms or more during the recovery phase or a maladaptive, paradoxical increase in QTc (P<.0001). Average QTc was longer in peak exercise in patients with LQT1 and LQT3 (P<.004), whereas in control patients and patients with LQT2, there was no significant difference at peak exercise (P<.90).
Patients with LQT1 displayed significant lengthened QTc during 5 minutes of recovery (P<.001). However, patients in the control group, LQT2 and LQT3 displayed a QTc that was the same or less than their baseline resting QTc, and throughout the 5 minutes of recovery, change QTc remained negative. In concealed LQT1 patients, QTc and change QTc increased at peak exercise, whereas QTc and change QTc decreased in patients with concealed LQT2 and concealed LQT3 (P<.0001).
“Our results refine and improve the diagnostic ability of treadmill stress test during the evaluation of patients with possible long QT syndrome by showing precisely where the greatest diagnostic separation resides, the recovery phase,” Michael J. Ackerman, MD, PhD, director of the Mayo Clinic’s Long QT Syndrome Clinic and the Windland Smith Rice Sudden Death Genomics Laboratory, said in a press release. “We hope that this targeted approach to reading and measuring the QTc will not only help to catch long QT syndrome when it is there but to also help decrease the current rate of overdiagnosis of long QT, which has resulted from misinterpretations of stress tests, and ultimately improve patients’ quality of life.”
Disclosure: This research program was supported by the Mayo Clinic. Dr. Ackerman reports being a consultant for Transgenomic and chair of its FAMILION Medical/Scientific Advisory Board.
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