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ECG interpretation sinus rhythm QTc prolongation criteria
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12-lead ECG normal values PR QRS QT intervals axis
GradeResponse
GradeResponse
Here is a thorough, systematic interpretation of this ECG:
ECG Interpretation — 04/04/26, 11:12
Machine-Reported Parameters
| Parameter | Value | Normal Range |
|---|---|---|
| Rate | 98 bpm | 60–100 bpm |
| PR interval | 123 ms | 120–200 ms |
| QRS duration | 83 ms | <120 ms |
| QT | 370 ms | Rate-dependent |
| QTc | 473 ms | ≤440 ms (M) / ≤460 ms (F) |
| P axis | 54° | 0–75° |
| QRS axis | 33° | -30° to +90° |
Settings: 25 mm/s, 10 mm/mV limb and chest leads, filter 0.15–100 Hz
Systematic Interpretation
1. Rhythm
Sinus rhythm. P waves are upright in I and II (axis 54°), confirming sinus origin. Regular rhythm at 98 bpm.
2. Rate
98 bpm — high-normal, approaching sinus tachycardia threshold.
3. Conduction
- PR interval: 123 ms — low-normal/short-normal, no AV block, no pre-excitation (no delta waves visible)
- QRS duration: 83 ms — normal, no bundle branch block
4. Axis
- QRS axis: +33° — normal axis
- P axis: +54° — normal
5. QTc — ⚠️ PROLONGED
The QTc of 473 ms is prolonged (normal upper limit ~440 ms in men, ~460 ms in women). This is the most clinically significant finding on this tracing.
- The machine uses Bazett's formula (QTc = QT / √RR)
- QTc 473 ms falls in the borderline-to-mildly prolonged range
- Risk of Torsades de Pointes increases significantly above 500 ms, but any QTc >440–460 ms warrants attention
6. P Waves
Normal morphology and axis. No evidence of atrial enlargement.
7. QRS Morphology
- No pathological Q waves visible
- Precordial R-wave progression appears normal (R wave grows V1→V5/V6)
- No LVH or RVH voltage criteria apparent
8. ST Segments & T Waves
No ST elevation or depression. T waves appear upright in lateral leads. No obvious acute ischemic changes.
Machine Diagnosis vs. Human Review
| Machine | Human Review | |
|---|---|---|
| Primary interpretation | "Normal ECG" | Not fully normal — QTc is prolonged at 473 ms |
| Rhythm | Sinus ✓ | Sinus ✓ |
| Rate | Normal ✓ | High-normal ✓ |
The machine labeled this "NORMAL ECG" — however, the QTc of 473 ms is above normal limits and should not be dismissed.
Clinical Significance of QTc 473 ms
Causes to consider:
- Medications (most common) — antiarrhythmics (amiodarone, sotalol), antipsychotics (haloperidol, quetiapine), antibiotics (azithromycin, fluoroquinolones), antihistamines, methadone
- Electrolyte abnormalities — hypokalemia, hypomagnesemia, hypocalcemia
- Structural/functional — myocarditis, cardiomyopathy, post-MI
- Congenital long QT syndrome (Romano-Ward, Jervell-Lange-Nielsen)
- Hypothyroidism, hypothermia
Recommended actions:
- Check electrolytes (K⁺, Mg²⁺, Ca²⁺)
- Review current medications for QT-prolonging drugs
- Serial ECGs if on offending agents or if symptomatic (syncope, palpitations)
- Cardiology referral if QTc persistently >500 ms or symptomatic
Summary
Sinus rhythm at 98 bpm. Normal axis. Normal PR and QRS duration. QTc is prolonged at 473 ms — this is the key abnormality. No acute ischemic changes. Machine interpretation as "Normal ECG" is inaccurate regarding the QTc.
(Based on AHA/ACC ECG standardization guidelines and Harrison's Principles of Internal Medicine, 21st ed., p. 6812)
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