Here, investigators from the Mayo Clinic show how the recovery phase displays significant and maladaptive changes in the QTc unveiling the most common LQTS type, LQT1. The study, published in the November edition of HeartRhythm, the official journal of the Heart Rhythm Society, is the largest, single-center study of treadmill exercise stress testing in patients with genetically proven LQTS, as well as those who were dismissed as normal.
Long QT syndrome affects about 1 in 2,500 individuals, and nearly 40 percent of patients with LQTS can have a nondiagnostic QTc at rest. However, through treadmill stress testing, this new study reveals significant differences in QTc values for the three primary types of LQTS (LQT1-LQT3) at a specific moment in time during the exercise test. QTc was calculated at rest, peak exercise and for the first five minutes of recovery.
Between 1998 and 2008, more than 1,000 patients with a referral diagnosis of LQTS were seen at the Mayo Clinic’s Long QT Syndrome Clinic in Rochester, Minn. Of these patients, an Institutional Review Board-approved, retrospective analysis was performed on the treadmill stress test in 243 individuals including, 82 LQT1, 55 LQT2, 18 LQT3, and 88 genotype-negative patients (control group) dismissed as normal.
Results of the treadmill exercise stress test reveal the following:
• Maladaptive QTc prolongation during the recovery phase distinguishes LQTS, particularly LQT1 patients, from the control group.
• Specifically, patients with LQT1 most distinguished themselves from the other genotypes and the controls at 2 and 3 minutes of recovery.
• Beta-blockers did not significantly obscure the response noted during the recovery phase, which eliminates the need for a beta-blocker washout.
Overall, even with nondiagnostic QTc at rest, a prolonged QTc (> 470 ms) seen in patients at 3 minutes of recovery provides at 75% pre-genetic test probability for LQT1.
“Our results refine and improve the diagnostic ability of treadmill stress tests during the evaluation of patients with possible long QT syndrome by showing precisely where the greatest diagnostic separation resides, the recovery phase,” stated lead author Michael J. Ackerman, MD, PhD, director of Mayo Clinic’s Long QT Syndrome Clinic and the Windland Smith Rice Sudden Death Genomics Laboratory in Rochester, Minn. “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.”
Over the past two decades, other diagnostic tools used in the evaluation of LQTS have increased dramatically including genetic testing and provocative testing with catecholamines, like the epinephrine QT stress test. However, unlike exercise stress tests, the epinephrine QT stress test is not available at many centers and without appropriate experience in detecting the LQT1 response during epinephrine, it can be challenging to interpret. In contrast, exercise stress tests, such as treadmill testing, is more readily available at cardiology centers around the country. As shown through this study, evaluating patients during the recovery phase of treadmill exercise testing can result in an accurate diagnosis of LQTS, and offers clinicians another approach to consider.
For more information about this study, please visit www.heartrhythmjournal.com.
About the Heart Rhythm Society
The Heart Rhythm Society is the international leader in science, education and advocacy for cardiac arrhythmia professionals and patients, and the primary information resource on heart rhythm disorders. Its mission is to improve the care of patients by promoting research, education and optimal health care policies and standards. Incorporated in 1979 and based in Washington, DC, it has a membership of heart rhythm professionals in more than 70 countries around the world.
About HeartRhythm Journal
HeartRhythm provides rapid publication of the most important science developments in the field of arrhythmias and cardiovascular electrophysiology (EP). As the official journal of the Heart Rhythm Society, HeartRhythm publishes both basic and clinical subject matter of scientific excellence devoted to the EP of the heart and blood vessels, as well as therapy. The journal is the only EP publication serving the entire electrophysiology community from basic to clinical academic researchers, private practitioners, technicians, industry and trainees. HeartRhythm Journal has an impact factor of 4.246 (as of 2011) and ranks 23rd out of 114 cardiovascular medicine journals worldwide by the Institute for Scientific Information, remaining the number one specialty journal in cardiology. It is also the official publication of the Cardiac Electrophysiology Society.
Contact: Kennesha Baldwin
Heart Rhythm Society