You are asked to admit a 63-year-old male with a history of hypertension and osteoarthritis. The patient, who fell at home, is scheduled for open repair of his femoral neck fracture the following day. The patient reports tripping over his granddaughter’s toys and denies any associated symptoms around the time of his fall. An electrocardiogram (ECG) reveals a QTc (QT) interval of 480 ms. How should this hospitalized patient’s prolonged QT interval be managed?
Patients with a prolonged QT interval on routine ECG present an interesting dilemma for clinicians. Although QT prolongation—either congenital or acquired—has been associated with dysrhythmias, the risk of torsades de pointes and sudden cardiac death varies considerably based on myriad underlying factors.1 Therefore, the principle job of the clinician who has recognized QT prolongation is to assess and minimize the risk of the development of clinically significant dysrhythmias, and to be prepared to manage them should they arise.
The QT interval encompasses ventricular depolarization and repolarization. This ventricular action potential proceeds through five phases. The initial upstroke (phase 0) of depolarization occurs with the opening of Na+ channels, triggering the inward Na+ current (INa), and causes the interior of the myocytes to become positively charged. This is followed by initial repolarization (phase 1) when the opening of K+ channels causes an outward K+ current (Ito). Next, the plateau phase (phase 2) of the action potential follows with a balance of inward current through Ca2+channels (Ica-L) and outward current through slow rectifier K+ channels (IKs), and then later through delayed, rapid K+ rectifier channels (IKr). Then, the inward current is deactivated, while the outward current increases through the rapid delayed rectifier (IKr) and opening of inward rectifier channels (IK1) to complete repolarization (phase 3). Finally, the action potential returns to baseline (phase 4) and Na+ begins to enter the cell again (see Figure 1, above).
The long QT syndrome (LQTS) is defined by a defect in these cardiac ion channels, which leads to abnormal repolarization, usually lengthening the QT interval and thus predisposing to ventricular dysrhythmias.2 It is estimated that as many as 85% of these syndromes are inherited, and up to 15% are acquired or sporadic.3 Depending on the underlying etiology of the LQTS, manifestations might first be appreciated at any time from in utero through adulthood.4 Symptoms including palpitations, syncope, seizures, or cardiac arrest bring these patients to medical attention.3 These symptoms frequently elicit physical or emotional stress, but they can occur without obvious inciting triggers.5 A 20% mortality risk exists in patients who are symptomatic and untreated in the first year following diagnosis, and up to 50% within 10 years following diagnosis.4