Five factors underlie the ongoing overdiagnosis and misdiagnosis of long QT syndrome (LQTS), including temporary QT prolongation following vasovagal syncope, a “pseudo”-positive genetic test result, family history of sudden cardiac death, transient QT prolongation, and misinterpretation of the QTc interval, a new study suggests.
Awareness of these characteristics, which led to a diagnostic reversal in 290 of 1,841 (16%) patients, could reduce the burden of overdiagnosis on the health care system and on patients and families, senior author Michael J. Ackerman, MD, PhD, of Mayo Clinic, Rochester, Minn., and colleagues conclude.
“The findings are a disturbing and disappointing sequel to the paper we published about LQTS overdiagnosis back in 2007, which showed that 2 out of every 5 patients who came to Mayo Clinic for a second opinion left without the diagnosis,” Dr. Ackerman told this news organization.
To date, Dr. Ackerman has reversed the diagnosis for 350 patients, he said.
The consequences of an LQTS diagnosis are “profound,” he noted, including years of unnecessary drug therapy, implantation of a cardioverter defibrillator, disqualification from competitive sports, and emotional stress to the individual and family.
By pointing out the five biggest mistakes his team has seen, he said, “we hope to equip the diagnostician with the means to challenge and assess the veracity of a LQTS diagnosis.”
The study was published online in the Journal of the American College of Cardiology.
Time to do better
Dr. Ackerman and colleagues analyzed electronic medical records on 290 of 1,841 (16%) patients who presented with an outside diagnosis of LQTS but subsequently were dismissed as having normal findings. The mean age of these patients at their first Mayo Clinic evaluation was 22, 60% were female, and the mean QTc interval was 427 ±25 milliseconds.
Overall, 38% of misdiagnoses were the result of misinterpretation of clinical factors; 29%, to diagnostic test misinterpretations; 17%, to an apparently positive genetic test in the context of a weak or absent phenotype; and 16%, to a family history of false LQTS or of sudden cardiac or sudden unexplained death.
More specifically, the most common cause of an LQTS misdiagnosis was QT prolongation following vasovagal syncope, which was misinterpreted as LQTS-attributed syncope.
The second most common cause was an apparently positive genetic test for an LQTS gene that turned out to be a benign or likely benign variant.
The third most common cause was an LQTS diagnosis based solely on a family history of sudden unexplained death (26 patients), QT prolongation (11 patients), or sudden cardiac arrest (9 patients).
The fourth most common cause was an isolated event of QT prolongation (44 patients). The transient QT prolongation was observed under myriad conditions unrelated to LQTS. Yet, 31 patients received a diagnosis based solely on the event.
The fifth most common cause was inclusion of the U-wave in the calculation of the QTc interval (40 patients), leading to an inaccurate interpretation of the electrocardiogram.
Dr. Ackerman noted that these LQTS diagnoses were given by heart-rhythm specialists, and most patients self-referred for a second opinion because a family member questioned the diagnosis after doing their own research.
“It’s time that we step up to the plate and do better,” Dr. Ackerman said. The team’s evaluation of the impact of the misdiagnosis on the patients’ lifestyle and quality of life showed that 45% had been restricted from competitive sports (and subsequently resumed sports activity with no adverse events); 80% had been started on beta-blockers (the drugs were discontinued in 84% as a result of the Mayo Clinic evaluation, whereas 16% opted to continue); and 10 of 22 patients (45%) who received an implanted cardioverter device underwent an extraction of the device without complications.
The authors conclude: “Although missing a patient who truly has LQTS can lead to a tragic outcome, the implications of overdiagnosed LQTS are not trivial and are potentially tragic as well.”