Approach to Discrepant Heart Rates on Two ECGs

Immediate Verification Steps

The American College of Cardiology recommends examining both ECGs for lead misplacement, which can alter computer-generated measurements and produce spurious heart rate calculations 1
The American College of Cardiology suggests verifying proper electrode positioning, as precordial lead misplacement occurs in more than one-third of routine recordings and can affect automated measurements 1
The American College of Cardiology advises looking for baseline wander, electrical interference, or poor electrode contact that may compromise automated heart rate detection 2
The American College of Cardiology recommends checking for pacemaker artifacts that may be missed by automated systems, particularly with modern low-amplitude bipolar pacing, leading to incorrect heart rate calculations 2

The American Heart Association notes that different ECG machines use proprietary algorithms that can produce substantially different measurements, even from the same cardiac electrical activity 5
The American College of Cardiology states that newer electrocardiographs typically use global measurements from simultaneous multilead acquisition, while older machines use single-lead measurements, resulting in systematic differences 4

The American College of Cardiology recommends reviewing prior tracings with correct technique to establish the patient's baseline heart rate pattern 1
The American College of Cardiology suggests that a heart rate change of ≥20 bpm crossing thresholds of 50 or 100 bpm constitutes a significant change requiring clinical correlation 7

The American College of Cardiology advises against assuming the computer-generated heart rate is accurate without manual verification, particularly when two measurements differ significantly 1
The European Society of Cardiology warns that blocked atrial bigeminy or other rhythm disturbances can simulate bradycardia if P waves are not carefully examined 8

The American College of Cardiology recommends documenting which measurement is correct and noting the reason for discrepancy (technical artifact, lead misplacement, algorithm difference) if manual calculation confirms one ECG is accurate 1
The American College of Cardiology suggests documenting both values with timestamps and clinical context if both measurements are technically accurate but differ due to physiologic variation 7