50. Long QT Syndrome
Definition
Long QT syndrome (LQTS) is prolonged duration of the QT interval in the cardiac cycle. This syndrome can be congenital or acquired. The congenital form may or may not be accompanied by deafness. Both forms have a propensity for ventricular dysrhythmias, which in turn may lead to unstable dysrhythmias (e.g., torsades de pointes, ventricular fibrillation), syncope, cardiac arrest, and/or sudden death.
Incidence
The true incidence of LQTS is difficult to estimate. It can be acquired or congenital, as a result of genetic mutations; approximately 10% to 15% of gene mutation carriers have normal QT C duration. Overall, LQTS may occur as frequently as 1:3000 to 1:5000.
Etiology
The congenital form of LQTS is the result of the mutation of cardiac ion channel genes. Thus far six chromosomal mutation locations and five specific genes have been identified. There are six variants of LQTS associated with Romano-Ward syndrome and two variants associated with Jervell and Lange-Nielsen syndrome. The prolongation of the QT interval occurs when the myocardial cells become overloaded with positively charged ions during the process of ventricular repolarization. This prolongation predisposes the patient to unstable ventricular dysrhythmias, particularly torsades de pointes, ventricular fibrillation, and sudden cardiac death. The appearance of ventricular dysrhythmias may be precipitated by any of a large number of adrenergic stimuli, including exercise, emotion, loud noises, atnd startle, but may occur spontaneously without preceding conditions or triggers. As a result, the patient with LQTS should be generally discouraged from participation in competitive sports.
LQTS can be acquired as a result of ingestion of various medications. The complete list of medications that may produce LQTS and/or an incidence of torsades de pointes is too large to be included in this volume, but it includes amiodarone, erythromycin, methadone, procainamide, and quinidine. A complete list of the medications can be found at www.qtdrugs.org/medical-pros/drug-lists/list-01.cfm.
Signs and Symptoms
• Aborted cardiac arrest
• Congenital deafness
• Family history of sudden cardiac death (especially at a young age)
• Notched T-wave in three leads
• Slow heart rate for patient age
• Sudden death
• Syncope
• Torsades de pointes
• T-wave alternans
Medical Management
The pharmacologic choice for management of LQTS is the use of a β blocker. β Blockers reduce the risk of cardiac dysrhythmia by blocking the adrenergic response. Until recently β blockers have been given in large doses (e.g., propranolol, 3 mg/kg/day). Current data suggest that a smaller dose may deliver protective effects similar to that observed with the larger doses. The most commonly used β blockers are propranolol and nadolol, although atenolol and metoprolol are also frequently prescribed. β Blockade is not a curative treatment. About 70% of LQTS patients are effectively treated (i.e., cardiac events are prevented) with β blockers; however, about 30% may still experience a cardiac event. Gene-specific therapy is not presently available to treat the alteration or mutations to the relevant ion channel(s).
A patient deemed to be at greatest risk for a cardiac event may benefit from having a cardioverter-defibrillator implanted. A higher risk patient is defined as one who has experienced an aborted cardiac arrest, has recurrent cardiac events despite conventional pharmacologic therapy, or uses β blockers combined with a cardiac pacemaker and/or stellectomy. Left cervicothoracic stellectomy may be used as an antiadrenergic therapy in a high-risk LQTS patient.
Complications
• Cardiac arrest
• Neurologic deficits (after an aborted cardiac arrest)
• Sudden death
• Torsades de pointes
• Ventricular fibrillation
Anesthesia Implications
First and foremost, the patient with LQTS must continue the usual oral dose of β blocking medication(s) on the operative day. Anxiety should be treated prophylactically with a preoperative anxiolytic medication, “erring” on the larger end of the dosage range. To minimize adrenergic stimulation, the patient should ideally be deeply anesthetized before any attempt at direct laryngoscopy. The anesthetic course should be charted with every effort directed at minimizing adrenergic stimulation. The technique should rely fairly heavily on opioid administration to blunt or suppress adrenergic response to noxious stimulation. Nitrous oxide should not be used because of its inherent mild sympathetic stimulation. For this same reason, desflurane should not be the volatile agent chosen for the maintenance of general anesthesia. Epinephrine should be avoided, whether in conjunction with regional anesthesia or for treatment of hypotension or bradycardia. Isoflurane and sevoflurane are each known to prolong the QT interval and are best avoided; halothane reduces the QT interval and may be used if it is available. Propofol also reduces the QT interval as well as QT dispersion. Total intravenous anesthesia (TIVA) may be the most appropriate choice for the patient with LQTS. At the conclusion of surgery it may be appropriate to extubate the patient while he or she is still relatively deeply anesthetized—unless there are contraindications such as gastroesophageal reflux disease (GERD) or morbid obesity—to minimize any anxiety and/or adrenergic stimulation during the emergence process. For longer, more extensive surgical procedures, a supplemental infusion of a β blocker may be indicated. This infusion should be continued into the postanesthesia care phase before being tapered to discontinuation. Pain must be adequately controlled postoperatively, along with any nausea or vomiting.
