What to do for prolonged QTc (QT interval corrected)?

From the Guidelines

For QTc prolongation, immediate actions include discontinuing any QT-prolonging medications and checking and correcting electrolyte abnormalities, especially potassium and magnesium, as the risk of adverse events increases with QTc >500 ms 1. When managing QTc prolongation, it is crucial to prioritize maintaining normal potassium and magnesium balance, as hypokalemia or hypomagnesemia can precipitate episodes of torsades de pointes. Key considerations include:

• Discontinuing QT-prolonging medications, as their use can increase the risk of adverse events in patients with long QT syndrome 1
• Maintaining potassium levels >4.0 mEq/L and magnesium levels >2.0 mg/dL to reduce the risk of torsades de pointes
• Avoiding concurrent use of stimulant or non-stimulant attention deficit/hyperactivity medications, which may increase the risk of syncope or cardiac arrest in patients with long QT syndrome, particularly in males 1
• Reducing fever with antipyretics, as rare case reports suggest that fever can prolong the QT interval in patients with long QT syndrome type 2 1 Hospital admission for cardiac monitoring should be considered if the QTc is severely prolonged (>500 ms) 1. In patients with congenital long QT syndrome, beta-blockers like nadolol or propranolol are first-line treatments, and patients should be educated about symptoms of arrhythmias, including palpitations, dizziness, syncope, and seizures, which warrant immediate medical attention.

From the FDA Drug Label

The necessary treatment of hemodynamically unstable polymorphic ventricular tachycardia (including torsades de pointes) is withdrawal of treatment with quinidine and either immediate cardioversion or, if a cardiac pacemaker is in place or immediately available, immediate overdrive pacing. After pacing or cardioversion, further management must be guided by the length of the QTC interval Factors contributing to QTC prolongation (especially hypokalemia, hypomagnesemia, and hypocalcemia) should be sought out and (if possible) aggressively corrected Prevention of recurrent torsades may require sustained overdrive pacing or the cautious administration of isoproterenol (30 to 150 ng/kg/min).

The management of QTC interval prolongation involves:

• Withdrawal of quinidine treatment
• Cardioversion or overdrive pacing for hemodynamically unstable polymorphic ventricular tachycardia
• Correction of underlying factors contributing to QTC prolongation, such as hypokalemia, hypomagnesemia, and hypocalcemia
• Sustained overdrive pacing or cautious administration of isoproterenol to prevent recurrent torsades 2

From the Research

QTc Interval Prolongation Management

To manage QTc interval prolongation, several steps can be taken:

• Identify patient-related risk factors, such as female sex, age >65 years, and uncorrected electrolyte disturbances 3
• Assess the potential risk and degree of QT prolongation associated with the proposed drug 3
• Consider co-prescribed medicines that could increase the risk of QT prolongation 3
• Use a simple algorithm to guide clinical management in patients at risk of QT prolongation/TdP 3

Monitoring and Prevention

Regular monitoring of electrocardiography (EKG) and electrolytes is necessary to prevent TdP:

• Patients at risk for QT interval prolongation should be educated to go directly to the emergency room if they experience palpitations, lightheadedness, dizziness, or syncope 4
• When the QTc interval is 470-500 ms for males or 480-500 ms for females, or the QTc interval increases 60 ms or more from pretreatment values, dose reduction or discontinuation of the offending drug should be considered 4
• If the QTc interval is ≥500 ms, the offending drug should be discontinued, and continuous EKG telemetry monitoring should be performed, or the 12-lead EKG should be repeated every 2-4 hours, until the QT interval has normalized 4

Measurement and Interpretation

Measurement and interpretation of the QT interval can be challenging:

• Automated ECG printouts cannot be relied upon to diagnose QT interval prolongation; thus, the onus is on the clinician to identify it 5
• A wealth of correctional formulae have been derived, but none has proven superior 5
• A step-by-step guide to manually measuring and correcting the QT interval can be useful in common hospital-based clinical scenarios 5

Risk Factors and Associations

Several risk factors and associations are related to QTc interval prolongation:

• Hypokalemia, female sex, drug-drug interactions, advancing age, genetic predisposition, hypomagnesemia, heart failure, bradycardia, and corrected QT (QTc) interval prolongation are risk factors for drug-induced TdP 4
• Many drugs, including pain medications, antipsychotics, and antidepressants, can increase the risk of QT prolongation 6, 7
• Slow dose titration and electrocardiography monitoring are recommended when using drugs that may increase the risk of QT prolongation 6