Normal range of PQRST axis
In the field of electrocardiogram (ECG) measurement and analysis in medicine, identification of the PQRST waveform segments is a critical issue. For many ECG features, determining the normal range of the PQRST axis is essential.
Normal Range of the PQRST Axis
The normal PQRST axis falls between –30° and +90°. When interpreting an ECG, one must first examine the horizontal (time) and vertical (voltage) axes. Each horizontal small division represents 0.04 seconds, while each vertical small division corresponds to 0.1 mV. In a normal ECG, the P-wave duration is typically less than 0.12 seconds—equivalent to fewer than three horizontal divisions. Its amplitude is measured vertically: in most limb leads, it is less than 2.5 divisions; in precordial leads, less than 2 divisions. The P wave reflects atrial depolarization. The QRS complex duration is normally less than 0.11 seconds, commonly ranging from 0.06 to 0.10 seconds. Furthermore, the morphology and amplitude of the QRS complex often differ across precordial leads. The R wave progressively increases in amplitude from right to left—reflecting proximity to the left ventricle. On the ECG, this manifests as a gradual increase in R-wave amplitude from lead V1 to V5, with the R wave in V6 typically smaller than that in V5. The QRS complex represents ventricular depolarization. The T wave usually points in the same direction as the main deflection of the QRS complex in most leads, and its amplitude generally exceeds one-tenth of the corresponding R-wave amplitude in the same lead.
The PQRST mnemonic is commonly used for patients presenting with pain. The five letters—P, Q, R, S, and T—are consecutive in the alphabet and correspond precisely to the sequence of major waveform components in the ECG, making this mnemonic easy to remember and apply.
ECG waveforms represent the electrical activity of the heart within the body, with each waveform corresponding to a specific phase of cardiac electrophysiology. We hope this explanation proves helpful!
