|ECG ChallengeMay, 2008
A 34-year-old woman is evaluated prior to surgical repair of a torn medial meniscus of the right knee. Her knee pain began about two years ago, was gradual in onset, and was not a result of injury or antecedent events. During the last two weeks, her pain has become significantly more severe. She describes it as “throbbing,” “sharp,” and “constant,” rating it 10 out of 10 on a pain scale. The pain worsens with any activity, including walking or bending, and has not responded to NSAIDs or oxycodone. MRI confirmed a “bucket-handle” tear of the medial meniscus of the right knee.
Medical history is remarkable for anxiety disorder, depression, type 2 diabetes mellitus, hypertension, and hypercholesterolemia. There is no prior surgical history. The patient’s family history is significant for diabetes and hypertension. Her mother died suddenly from a “heart condition” at age 40.
The patient denies a history of smoking or recreational drug use, but she does have a history of alcohol abuse. Her last use of alcohol was six months ago. Symptom review reveals four episodes of syncope during the last year, which were attributed to her anxiety disorder by her mental health care provider. The remainder of the systems review is noncontributory.
The patient has no drug allergies. Her current medication list includes atenolol (100 mg/d), lisinopril (40 mg bid), atorvastatin (80 mg/d), metformin (1,000 mg in the morning and 500 mg at night), levetiracetam (1,000 mg bid), and mirtazapine (45 mg at bedtime).
Preoperative laboratory data are within normal limits, and the chest x-ray is normal. An ECG shows the following: a ventricular rate of 108 beats/min; PR interval, 130 ms; QRS duration, 84 ms; QT/QTc interval, 400/536 ms; P axis, 61°; R axis, 59°; and T axis, 37°. What is your interpretation of this ECG—and is there anything in the patient’s history to warrant concern?
|ECG ChallengeMay, 2008
The ECG is remarkable for sinus tachycardia at a rate of 108 beats/min. PR and QRS intervals are normal; however, the patient has prolonged QT/QTc intervals. Given a family history suspicious for sudden cardiac death, four episodes of syncope during the last year, and prolonged QT/QTc intervals, a diagnosis of long QT syndrome should be strongly suspected.
Long QT syndrome is an inherited autosomal dominant mutation in one of five genes (KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2) that regulate the ion channels responsible for myocardial conduction. The gene variant occurs on a nonsex chromosome, so that each child of an affected parent has a 50% chance of inheriting it.
The diagnosis can be made based on an ECG in 50% of cases; however, in another 40% of cases, the QT interval is not sufficiently prolonged to make a definitive diagnosis, and in the remaining 10% of cases, the initial ECG will look normal. Subsequent genetic testing confirmed the diagnosis of long QT syndrome in this patient.