Hello NAVE Crew! In this fourth episode of the NAVE WAVES series, Understanding ECG in anesthesia, we gonna talk about ECG waveforms and highlight the most common changes in the ECG during anesthesia.
Electrocardiography, also known as ECG or EKG, is a composite of several sequenced waves, representing the electrical activity generated by the heart in one beat. To understand how to get ECG waves, we need to remember that the heart is a muscle with rhythmic electrical conduction. As long as it is healthy, it will always generate the first stimulus in a specific place and then propagate it to other parts of the organ.
The trigger is called the Sinoatrial node, located in the right atrium. The impulse goes towards the atrioventricular node and, after, to the ventricles, through the Hiss bundle, located in the interventricular septum. Then, the impulse reaches the Purkinje fibres, forming the electrocardiogram waves.
We generally use Einthoven's bipolar leads I, II and III to obtain ECG waves in anaesthesia. The standard ECG wave has a usual form: The first wave is called "P wave", which indicates the atrial depolarization, and is positive. The second one is called the "QRS complex, " representing ventricular depolarization. The last one is called the "T wave", representing ventricles repolarization, which is usually positive, with a maximum size of 25% of the R wave. It is important to understand that the wave generated by atrial repolarization is generally not observed, as the QRS complex superimposes it.
We use the base-apex derivation in horses and cattle, which gives us a slightly different reading, with an inverted QRS complex. The T wave can be positive or biphasic. Another very important detail is that the P wave can be bifid in adult horses, due to the size of the atria.
The electrocardiogram interpretation during anaesthesia is much more dynamic than in clinical medicine. That's because we take a faster reading, without measuring wave sizes, and trying to correlate with drugs or events during anaesthesia. The most common changes in the ECG waveforms during anaesthesia are sinus bradycardia, sinus arrest, 1st and 2nd-degree atrioventricular block, sinus tachycardia, premature ventricular complex, ventricular escape and premature atrial complex.
Find out more watching the video!
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Additional Material
- Carregaro AB, Silva ANE. Monitoração Anestésica. In: Luna SPL, Carregaro, AB. Anestesia e Analgesia de Equideos, Ruminantes e Suínos. 247-280, 2019.
- ECG Educator Blog. ecg-educator.b...
- Kaese et al. Herzschrittmacherther Elektrophysiol, 24:84-91,2013.
- Tilley LP. Essentials of canine and feline electrocardiography: Interpretation and treatment. Lea & Febiger, 500p, 1992.
Additional credits
heart video - • Cardiac Conduction Sys...
ECG waveform video - • EKG/ECG Interpretation...
Final musci - Level Up - Quincas Moreira
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NAVE was created in 2005 and its main objective is to disseminate videos and webseries aimed at Veterinary Medicine students and professionals who work in the field of veterinary anesthesiology.
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