From the Guidelines
To measure the QRS complex on an electrocardiogram (ECG), identify the beginning of the Q wave (or R wave if Q is absent) to the end of the S wave, and calculate the duration in seconds or milliseconds, as recommended by the American Heart Association 1. Normal QRS duration is 0.06-0.10 seconds (60-100 milliseconds) 1. Use ECG paper where each small box equals 0.04 seconds, so a normal QRS spans 1.5-2.5 small boxes. Count the boxes the QRS occupies and multiply by 0.04 seconds per box. For accurate measurement, use leads with the clearest QRS complexes, typically leads I, II, or V1 1. A prolonged QRS (>0.12 seconds) may indicate conduction abnormalities like bundle branch blocks or ventricular hypertrophy 1. QRS measurement is important because it reflects how quickly electrical impulses travel through the ventricles, with prolongation suggesting impaired conduction that may require further evaluation or treatment 1. Some key points to consider when measuring the QRS complex include:
- The QRS complex should be measured from the beginning of the Q wave (or R wave if Q is absent) to the end of the S wave 1.
- The lead with the clearest QRS complex should be used for measurement, typically leads I, II, or V1 1.
- The QRS duration should be calculated in seconds or milliseconds, with a normal duration of 0.06-0.10 seconds (60-100 milliseconds) 1.
- A prolonged QRS (>0.12 seconds) may indicate conduction abnormalities and requires further evaluation or treatment 1. The most recent and highest quality study on this topic is from 2019, which provides updated guidelines for the measurement and interpretation of the QRS complex 1. Therefore, the most accurate and reliable method for measuring the QRS complex is to use the guidelines outlined in the 2019 study 1.
From the Research
Measuring QRS
To measure the QRS complex, it is essential to understand its components and the ventricular conduction system. The QRS complex is composed of the electrical currents originating from ventricular depolarization 2.
Key Components of QRS Measurement
- The QRS duration can be measured from a 12-lead ECG 3
- The effects of sodium channel blockers on QRS duration can be examined 3
- QRS interval prolongation can be measured as changes in the QRS interval on the ECG 4
- The QRS complex is responsible for the synchronized and almost simultaneous activation of both ventricles 2
Factors Affecting QRS Measurement
- Sodium channel blockers can increase QRS duration 3
- The potency of sodium channel blockers can affect QRS duration 3
- High-rate pacing can modify the arrhythmogenic substrate of Brugada syndrome and affect QRS measurement 5
- Epicardial fibrosis can compromise impulse conduction at the BrS fibrotic substrates and affect QRS measurement 5