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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Pause-dependent polymorphic ventricular tachycardia occurs in the presence of a prolonged QT interval (ECG pattern often resembles twisting around a point, hence the name)

  • Torsades de pointes in congenital long QT syndrome (LQTS) is not pause dependent:

    • – It is referred to as adrenergic torsades de pointes

    • – It is secondary to delayed after depolarizations (DADs) due to prolonged refractory period of the cardiac action potential

GENERAL CONSIDERATIONS

  • Lengthening of the pause-dependent action potential provides the substrate for the arrhythmia

  • QT prolongation may be induced by:

    • – Medications such as class IA and III antiarrhythmic drugs

    • – Antibiotics such as erythromycin (macrolides), fluoroquinolones

    • – The phenothiazine group of drugs

    • – Metabolic states such as hypokalemia and hypomagnesemia

  • Antihistamines such as terfenadine can cause QT prolongation (avoid in combination with macrolide antibiotic)

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Family history of LQTS in some

  • Malignant syncope

  • Lightheadedness

  • Palpitations

  • Sudden cardiac death

PHYSICAL EXAM FINDINGS

  • Deafness as part of congenital LQTS

DIFFERENTIAL DIAGNOSIS

  • Polymorphic ventricular tachycardia secondary to acute ischemia (QT interval may be normal)

  • Catecholamine-dependent polymorphic ventricular arrhythmia

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Serum potassium

  • Serum magnesium

  • Cardiac biomarkers

  • Basic metabolic panel

ELECTROCARDIOGRAPHY

  • ECG usually shows prolonged QT interval

  • Telemetry for arrhythmia detection

  • Outpatient cardiac monitoring if patient complains of palpitations or syncope but has no documented arrhythmia

IMAGING STUDIES

  • Echocardiogram to evaluate left ventricular function and evaluate for structural heart disease

TREATMENT

CARDIOLOGY REFERRAL

  • All patients should be evaluated by a cardiologist and preferably by an electrophysiologist at the cardiologist’s discretion

HOSPITALIZATION CRITERIA

  • All patients must remain hospitalized until the problem resolves and secondary prevention is addressed

MEDICATIONS

  • Patients with hemodynamic collapse require emergent electrical countershock

  • Stable patients can start with aggressive boluses of IV magnesium

  • For frequent pauses, consider temporary pacing (ideally atrial pacing) or IV isoproterenol

  • Eliminate medications that prolong the QT interval

  • Beta blockers for congenital LQTS

THERAPEUTIC PROCEDURES

  • Implantable cardioverter-defibrillator (ICD) in patients with congenital LQTS

MONITORING

  • ECG monitoring in the hospital

DIET AND ACTIVITY

  • No long-term restrictions recommended

ONGOING MANAGEMENT

HOSPITAL DISCHARGE CRITERIA

  • Once the acute symptoms and arrhythmia resolve

  • After an ICD implantation in patients with LQTS

FOLLOW-UP

  • Two weeks after hospital discharge

  • Outpatient cardiac monitor to document arrhythmia ...

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