Normal ECG Values Chart and Trace Explained

An electrocardiogram is an essential diagnostic test in the domain of cardiac care. Through this test, the electrical activity of the heart is measured and various abnormalities are detected. Understanding the normal ECG values chart is pivotal for interpreting the results of the ECG test accurately. The intricacies of the normal ECG values hold great significance in healthcare, as the normal ECG values chart give vivid insights into the impulses produced by the heart during its electrical activity which are illustrated in the recording device.

The Normal ECG Trace and Square Sizes

A normal ECG trace includes a P wave, a QRS complex and a T wave. In order to assess these correctly, the standard ECG is recorded at a speed of 25mm/sec and gain of 10mm/mV. The square sizes on the recording are defined as follows:

• 40ms = 1mm = 1 small square
• 200ms = 5mm = 1 large square
• 0.1mV = 1mm = 1 small square

Core Components of the ECG Waveform

The ECG waveform consists of several components with each component representing a different electrical event within the heart. These components give insights into cardiac function and identify abnormalities.

P-Wave

The P wave is indicative of atrial depolarisation. In this, electrical impulses initiate from the natural pacemaker of the heart, i.e. sinoatrial node, and propagate through the upper chambers of the heart, i.e. atria. In the standard electrocardiogram, the duration of the P wave is 0.06 to 0.11 seconds. Moreover, the amplitude of the P wave is up to a height of 2.5 mm. A normal P-wave is an indicator of normal depolarization.

QRS Complex

The QRS complex is indicative of ventricular depolarisation. In this, the electrical impulses originating from the SA node spread through the ventricles. A normal QRS complex has a duration that ranges from 0.06 to 0.10 seconds. Furthermore, the amplitude of the complex is up to a height of 5mm.

T-Wave

The T wave is indicative of ventricular repolarisation, signifying the recovery phase of the ventricles post-depolarization. In the standard electrocardiogram, the T-wave has a duration that ranges from 0.16 to 0.24 seconds. Additionally, the amplitude of the T-wave is of a height of up to 5 mm. Deviations from these standard units can indicate T-wave abnormalities that can cause electrolyte imbalances or myocardial ischemia.

Additional ECG Parameters and Intervals

Apart from the basic ECG components, there are some additional ECG parameters in the normal ECG values chart. Through these additional parameters, we get insights into various cardiac functions:

• PR interval: the time between atrial depolarisation and ventricular depolarisation, suggestive of AV conduction time. In a normal PR interval, the time period taken ranges from 0.12 to 0.20 seconds. This reflects the conduction of electrical impulses from the atria to the ventricles through the atrioventricular node.
• QT interval: the time between ventricular depolarisation and repolarisation. It typically ranges from 0.36 to 0.44 seconds at a heart rate of 60 to 100 beats per minute. Any deviation from this unit can be likely due to cardiac arrhythmia.
• Heart rate: normally expressed in beats per minute, is a critical factor in the assessment of an electrocardiogram.

The Standard 12-Lead ECG System

A standard 12-lead ECG includes bipolar limb leads, unipolar limb leads and chest leads. Electrical potential difference is measured between the electrodes to monitor different areas of the heart.

Bipolar Limb Leads

• Lead I: RA to LA (Direction: 0) — Lateral
• Lead II: RA to LL (Direction: +60) — Inferior
• Lead III: LA to LL (Direction: +120) — Inferior

Unipolar (Augmented) Limb Leads

• aVL: LA (Direction: -30) — Lateral
• aVR: RA (Direction: -150) — Right atrial
• aVF: LL (Direction: +90) — Inferior

Unipolar Chest Leads

• V1: Right atrial
• V2: Septal
• V3 & V4: Anterior
• V5 & V6: Lateral