EKG Monitoring When Starting Nortriptyline
Obtain a baseline EKG before initiating nortriptyline and monitor for QRS widening, PR interval prolongation, QTc prolongation, and heart rate changes, as tricyclic antidepressants produce significant cardiac conduction effects that can lead to life-threatening arrhythmias. 1, 2
Critical EKG Parameters to Monitor
Pre-Treatment Baseline Assessment
- A baseline EKG is mandatory before starting nortriptyline, as recommended by the American College of Cardiology for all patients initiating psychotropic agents like tricyclic antidepressants 1
- Document baseline heart rate, PR interval, QRS duration, and QTc interval to enable detection of drug-induced changes 2, 3
Key EKG Changes to Monitor During Treatment
QRS Duration (Most Critical Parameter)
- QRS widening ≥0.10 seconds (100 msec) is the best indicator of tricyclic antidepressant toxicity severity and warrants immediate dose reduction or discontinuation 2
- QRS widening >50% from baseline requires dose reduction or discontinuation 4
- Nortriptyline causes statistically significant increases in QRS duration even at therapeutic doses 3, 5, 6
PR Interval Prolongation
- Monitor for first-degree AV block (PR >200 msec), which can develop during nortriptyline treatment 3, 5
- PR interval increases correlate with plasma nortriptyline concentrations 3
- Significant PR prolongation occurred in elderly patients with higher metabolite levels 3
QTc Interval
- Monitor for QTc prolongation >440 msec, which increases risk of torsades de pointes 1, 6
- Changes in QTc interval correlate with nortriptyline metabolite concentrations 3
Heart Rate
- Nortriptyline produces sinus tachycardia due to anticholinergic effects 2, 5, 7
- Monitor for heart rate >100 bpm (asymptomatic sinus tachycardia) 6
Timing of EKG Monitoring
Initial Monitoring Protocol
- Obtain baseline EKG before starting nortriptyline 1, 2
- Repeat EKG after initiation of therapy, typically within 1-2 weeks at steady state 1
- Additional EKGs are indicated after any dosage changes 1
Ongoing Monitoring
- Serial ECGs should be obtained when doses exceed 100-120 mg daily, as this threshold is associated with increased cardiac risk 4
- More frequent monitoring is required if other QT-prolonging medications are added 1
High-Risk Populations Requiring Enhanced Monitoring
Patients Requiring Immediate EKG and Cardiac Monitoring
- Patients with pre-existing cardiovascular disease, including structural heart disease or history of arrhythmias 2
- Elderly patients, who have higher metabolite levels that contribute to cardiotoxicity 3
- Patients taking other medications that prolong QT interval or affect cardiac conduction 1
- Patients with electrolyte abnormalities (hypokalemia, hypomagnesemia, hypocalcemia) 1
Management of Abnormal EKG Findings
When to Discontinue or Reduce Nortriptyline
- QRS duration ≥0.10 seconds (100 msec) 2
- QRS widening >50% from baseline 4
- Development of second- or third-degree AV block 2
- QTc >500 msec 1
- New ventricular arrhythmias 2
Emergency Management of Cardiotoxicity
- Sodium bicarbonate should be used to maintain serum pH 7.45-7.55 for QRS widening and ventricular arrhythmias 2
- Hypertonic saline (7.5% NaCl) can reverse severe cardiotoxicity unresponsive to standard therapy 8
- Type 1A and 1C antiarrhythmics (quinidine, disopyramide, procainamide) are contraindicated 2
Common Pitfalls to Avoid
Critical Mistakes in EKG Monitoring
- Failing to obtain a baseline EKG makes it impossible to detect drug-induced changes and represents a critical error in patient safety 1, 4
- Neglecting to monitor electrolytes (potassium, magnesium, calcium), which can exacerbate QT prolongation and conduction abnormalities 1, 9
- Combining nortriptyline with other QT-prolonging drugs without cardiology consultation substantially increases risk of fatal arrhythmias 1, 4
- Underestimating cardiac risk in elderly patients, who develop higher metabolite concentrations that contribute to cardiotoxicity 3
Monitoring Frequency Errors