The ECG Leads: Introduction and Applications

By ANIWARE Veterinarian Dr. Hsieh

What is ECG Lead?

An ECG bipolar lead consists of two surface electrodes of opposite polarity, one positive and one negative. The electrodes record the animal heart’s electrical activity and present the ECG wave pattern. There are several Lead Systems with different directions and connection methods. Traditionally, 12-Lead ECG is the international standard Lead System.

In animal healthcare, primary care veterinarians often use the 6-Lead ECG. Other leads such as precordial lead are less suitable to apply on pets as there are great variations within breeds. For example in the case of deep-chested breeds, the precordial lead position would require adjustment. Overall, the leads record the magnitude of the cardiac potential activity and the directional current changes.

The Lead Systems details are shown below:

Source: Manual of Canine and Feline Cardiology 5th Edition

The standard limb lead, also known as 6-lead, record the heart depolarization changes on a frontal plane and the cardiac position and axis orientation. The 1 to 3 lead in limb lead (Lead I, II, III) is attached to the skin surface of the limbs to measure the spread and changes of the electrical activity within the heart. It is also known as the bipolar limb lead. In addition, as Lead II is most parallel and closest to the cardiac axis, it is considered as the most commonly used ECG lead.

How to choose between single-lead and multi-lead ECG?

A single-lead ECG is relatively simple to operate and providing result within a short period of time. Another reason why Lead II is the most commonly used single-lead is that the normal values of common ECG parameters are primarily calculated by Lead II. Hence, it is widely used in veterinary clinical practice for cardiac arrhythmia detection including bradycardia, tachycardia, sinus or non-sinus arrhythmia. Lead II can also detect conduction and electrolyte abnormalities, providing a preliminary evaluation of cardiac chamber patterns and heart disease tracking.

Since the procedure is relatively simple, fast and stress-free to the pet patient, Lead II is considered to be a routine test for high-risk group pets (aged pet or breeds at risk), pre-anaesthesia check and heart disease tracking. The insights provided by the ECG data serve as evidence for further investigations.

The common single-lead ECG in the market like CardioBird, backed by AI technologies and cardiologists to support primary care veterinarians. CardioBird assists in breaking through the limitations of time and resources. It serves as a good tool for veterinary professionals to perform initial cardiac assessments on animals!

Regarding multi-lead ECG (usually 6 or 12 leads), it is also called as diagnostic ECG. It gives a tracing from multiple electrical positions of the heart. Each lead records electrical activity from a different dimension and allows interpretation from different angles. The procedure of performing diagnostic ECG is much complicated and challenging in terms of data collection and interpretation. There are various diagnostic ECG brands currently available in the market. However, as mentioned that it requires advance ECG interpretation skills, the targeted users of diagnostic ECG are the veterinary cardiologists.

In conclusion, cardiologists recommend primary care veterinarians to integrate single-lead ECG into the clinical practice. With single-lead ECG, information about the rhythm and electrical conduction of the patient’s heart can be quickly obtained. In order to complete the initial cardiac assessment for the patient, auscultation of heart sounds including heart murmurs should also be performed to assess the condition of the cardiac structure. Further investigations, for example diagnostic ECG, Holter, X-ray, cardiac ultrasound, etc., can be conducted according to the single-lead ECG result.