ECG criteria
- Sinus tachycardia is the most frequent finding in mild to moderate overdose
- QTc prolongation: thresholds of men >450 ms and women >460 ms (Bazett) are frequently used; these thresholds depend on the correction formula and measurement technique. With tachycardia, the Fridericia formula is preferred because Bazett systematically overestimates QTc. QTc >500 ms is a marker of increased risk of torsades de pointes rather than an independent severity criterion for quetiapine intoxication per se.
- QRS complex widening >100 ms is a rare and non-specific finding; it requires evaluation for sodium channel blockade (as in TCA overdose) and general clinical status, and is not an independent severity criterion for quetiapine intoxication.
- Non-specific ST-T changes, T-wave flattening or inversion
- Sinus bradycardia or AV block are rare, non-specific signs of severe or co-ingested intoxication
- Non-specific intraventricular conduction delay is possible in massive or combined overdose; isolated signs such as a terminal R wave in aVR are not characteristic and not validated for quetiapine.
- Polymorphic ventricular tachycardia (torsades de pointes) in the setting of a prolonged QT interval is possible, but uncommon in isolated overdose.
- Dynamics on serial ECGs: monitoring of QTc and QRS width in the first hours after ingestion, especially with extended-release formulations.
What it looks like on ECG
The most frequent ECG finding in quetiapine overdose is sinus tachycardia, which is recorded even in mild to moderate intoxication. The QT interval is measured from the beginning of the QRS complex to the end of the T wave in the lead where the end of the T wave is most clearly defined and QT appears longest, usually II or V5; when in doubt, compare multiple leads. Heart rate correction is used (Bazett's QTc, Fridericia preferred in tachycardia). At toxic concentrations, quetiapine can inhibit hERG (IKr) potassium channels, and QTc may be prolonged; however, the magnitude of this effect depends on the dose, concomitant drugs, electrolytes, and baseline QT — the degree of prolongation cannot be predicted solely from the quetiapine dose.
QRS complex widening (>100 ms) is significantly less common than QT changes and is not a typical finding in isolated quetiapine overdose. If it appears, especially in the context of massive or combined intoxication, it warrants caution regarding clinically significant fast sodium channel blockade (similar to tricyclic antidepressants) and evaluation of the patient's general condition. Signs specific to sodium channel blockade, such as a terminal R wave in aVR, are not validated for quetiapine and should not be considered expected.
| Parameter | Parameter |
|---|---|
| HR | tachycardia — typical; bradycardia — rare, in severe/mixed intoxication |
| QTc | may be prolonged; clinical severity is unpredictable |
| QRS | usually normal; widening is rare, requires ruling out a sodium-channel effect |
| T wave | flattened, inverted, biphasic presentation possible |
| Rhythm | risk of torsades de pointes (rare in isolated overdose), ventricular arrhythmias |
For extended-release (XR) formulations, the toxic effect and ECG changes may have a delayed onset and persist longer. Any clinically significant overdose — regardless of the dosage form — requires observation and serial ECG recording according to the clinical protocol, as a single normal ECG does not rule out subsequent worsening of changes.
Mechanism
At toxic concentrations, quetiapine inhibits hERG (IKr) potassium channels, which are responsible for the rapid phase of ventricular repolarization, potentially prolonging the action potential and the QT interval. The magnitude of this effect is clinically less predictable than with potent and selective hERG blockers and often depends on the concurrent use of other QT-prolonging drugs and electrolyte disturbances. Prolonged repolarization and dispersion of refractoriness promote early afterdepolarizations and triggered polymorphic ventricular tachycardia (torsades de pointes).
At high concentrations, quetiapine may additionally, and to a lesser extent than tricyclic antidepressants, block fast sodium channels of cardiomyocytes, slowing depolarization. A clinically significant sodium channel effect in quetiapine poisoning is rare. In massive or combined overdose, intraventricular conduction disturbances, ventricular arrhythmias, and hemodynamic collapse are possible; however, the typical immediate cause of a severe outcome is more often CNS and respiratory depression, hypotension, and mixed intoxication, rather than a proven direct development of monomorphic ventricular tachycardia or asystole via a sodium-channel mechanism.
Causes
- Intentional quetiapine overdose (suicide attempt, the most frequent cause of severe cases)
- Accidental ingestion of a high dose, including in children
- Ingestion of extended-release (XR) formulations with potential delayed or prolonged toxicity course
- Co-ingestion with other QT-prolonging drugs (antiarrhythmics, certain antibiotics, other antipsychotics)
- Co-ingestion with CYP3A4 inhibitors that increase quetiapine concentrations
- Underlying electrolyte pathology (hypokalemia, hypomagnesemia) enhancing QT prolongation
Differential diagnosis
- Tricyclic antidepressant poisoning — QRS widening and a terminal R wave in aVR are typical for TCAs rather than quetiapine; differentiated by ingestion history, as routine toxicology screening often fails to detect quetiapine and may yield a false-positive reaction for TCAs
- Congenital long QT syndrome — absence of acute toxic history, QTc does not change dynamically after drug elimination
- Electrolyte disturbances (hypokalemia, hypomagnesemia) as an independent cause of QT prolongation — check potassium, magnesium, and calcium levels
- Poisoning with other QT-prolonging drugs (class IA/III antiarrhythmics, certain antipsychotics, antibiotics) — guided by the ingestion history
- Brugada type 1 pattern — ST elevation in right precordial leads V1–V2, including when recorded in the 2nd–4th intercostal spaces, without QT prolongation; distinguished from a toxic sodium-channel effect by clinical presentation, dynamics upon drug elimination, and the intoxication context
Clinical significance and management
Quetiapine poisoning can lead to torsades de pointes, ventricular tachycardia, and ventricular fibrillation in the setting of a prolonged QT, although such arrhythmias are uncommon in isolated overdose. Conduction abnormalities and hemodynamic collapse are possible in massive or mixed intoxication. Initial management involves ABC: assessment and protection of the airway, level of consciousness, and breathing; determining ingestion time, dose, and formulation; glucose, electrolytes (potassium, magnesium), renal function, and screening for co-ingestants (co-ingested drugs). Activated charcoal is considered according to the toxicology protocol shortly after ingestion of a potentially toxic dose, especially for extended-release (XR) formulations, and only with a protected airway.
The physician must record an ECG as early as possible, evaluate the QTc interval and QRS width, and repeat the ECG dynamically, as changes may progress in the first hours, especially with extended-release formulations. Rhythm monitoring in a setting that allows immediate defibrillation, along with monitoring and correction of electrolytes (potassium, magnesium), is indicated. Administration of sodium bicarbonate is not routine treatment for quetiapine overdose: it is considered in cases of marked QRS widening, hypotension, or ventricular arrhythmias with suspected clinically significant sodium channel blockade, with monitoring of pH and sodium levels, and after consultation with a toxicologist.
In torsades de pointes with hemodynamic instability (including when a pulse is present but unstable) or cardiac arrest, immediate unsynchronized defibrillation is indicated, regardless of whether magnesium has been administered yet. Alongside this, magnesium sulfate is administered intravenously regardless of baseline magnesium levels, potassium is corrected, and all QT-prolonging drugs are discontinued. For recurrent pause-dependent TdP after magnesium and electrolyte correction, heart rate acceleration is considered, primarily temporary cardiac pacing (overdrive pacing); isoproterenol can be used as a temporary measure in acquired drug-induced pause-dependent TdP, but not when congenital long QT syndrome is suspected. There is no specific antidote for quetiapine; treatment is symptomatic and supportive.
Common interpretation errors
- Assessing QT without heart rate correction — in tachycardia, uncorrected QT appears deceptively normal
- A single ECG without serial monitoring — changes can progress over several hours, especially with extended-release formulations
- Automatically attributing a typical TCA pattern (terminal R in aVR, right axis deviation) to quetiapine without sufficient grounds
- Ignoring concurrent hypokalemia and hypomagnesemia, which exacerbate QT prolongation
- Administering sodium bicarbonate solely based on overdose or moderate QT prolongation without clinical indications
1. Which ECG finding is most common in quetiapine overdose?
Sinus tachycardia is the most frequent and least specific finding in quetiapine overdose, including mild and moderate cases.
2. What is the electrophysiological mechanism underlying potential QT prolongation in quetiapine overdose?
At toxic concentrations, quetiapine can inhibit hERG potassium channels, slowing ventricular repolarization, although the clinical magnitude of the effect is unpredictable.
3. How typical is clinically significant torsades de pointes in isolated quetiapine overdose?
QTc prolongation is possible with quetiapine, but clinically significant torsades de pointes in isolated intoxication is rare and more commonly associated with additional risk factors.
Frequently asked questions
What is the main ECG sign of quetiapine poisoning?
The most frequent finding is sinus tachycardia. QTc may be prolonged, which theoretically creates a risk of torsades de pointes, but in isolated quetiapine overdose, clinically significant torsades de pointes is uncommon. QRS widening is possible but rare, and is associated with massive or mixed intoxication.
Is quetiapine poisoning dangerous to the heart?
Yes, in severe or mixed overdose, torsades de pointes, ventricular tachycardia, ventricular fibrillation, and hemodynamic collapse are possible, although such complications are uncommon in isolated overdose. The risk of ECG changes persists for several hours after ingestion, especially with extended-release formulations of the drug.
How to distinguish quetiapine poisoning from tricyclic antidepressant poisoning on ECG?
QRS widening and a terminal R wave in aVR are typical for tricyclic antidepressants rather than quetiapine, in which such changes are rare. They cannot be reliably distinguished by ECG alone; medical history and clinical presentation are crucial, and standard toxicological screening may have limited utility and yield cross-reactivity (false positives for TCAs).
Do I need to repeat the ECG in quetiapine poisoning?
Yes, a single normal ECG does not rule out risk, as changes, particularly with extended-release drug formulations, can progress over several hours.
What indicates a high degree of quetiapine cardiotoxicity?
The severity of intoxication is assessed primarily by the level of consciousness, respiration, hemodynamics, and ECG dynamics, rather than a single numerical threshold. QRS widening >100 ms and QTc >500 ms increase the risk of arrhythmias, while bradycardia and AV block are rare and non-specific signs of severe or mixed intoxication that require hemodynamic evaluation and investigation of other causes.
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Related terms
More in "Pharmacology and Toxicology"
Sources
- Goldberger's Clinical Electrocardiography, latest edition
- Surawicz, Knilans. Chou's Electrocardiography in Clinical Practice
- Orlov V.N. Guide to Electrocardiography
- AHA/ACCF/HRS Recommendations for Standardization and Interpretation of the ECG, 2009
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.