Electrocardiography

Basic Information

Overview and Goal(s)

• An electrocardiogram records the depolarization and repolarization process in atria and ventricles during the cardiac cycle.

• Electrocardiography is used to evaluate cardiac rate and rhythm. It allows the diagnosis of the nature of a dysrhythmia (eg, origin of ectopy, type of conduction disturbance).

Indications

• Monitoring:

Routine monitoring during general anesthesia and intensive care

Monitoring during treatment procedure (eg, antiarrhythmic drug administration such as quinidine)

Monitoring a patient at risk for developing arrhythmias (eg, due to electrolyte imbalance)

• Diagnosis of the presence and origin (ectopy, conduction disturbance) of an arrhythmia:

An arrhythmia detected on auscultation

Exercise intolerance

Clinical signs suggestive of syncope

Underlying cardiac or systemic disorders that might predispose to arrhythmias

Equipment, Anesthesia

• Electrocardiograph (ECG machine) to make the recording. This can be a large or small (handheld) recorder, or a recorder that transmits data wirelessly to a computer with appropriate software (Figures 1 and 2).

• Cable to connect the machine to the electrodes on the patient.

• Electrodes: Best results are obtained with self-adhesive (equine) electrodes. These are well tolerated, easy to use, and produce few artifacts. Crocodile clamps are more painful and produce more movement artifacts, although they are also often used.

• The ECG trace can be displayed on a screen, recorded on paper, or digitally recorded (digital media, computer).

• A single lead recording is satisfactory in most cases. However, multiple lead recordings may be helpful in some situations.

FIGURE 1 Example of recording an ECG using one type of ECG (wireless) equipment. 1, A battery powered recorder (Televet100) records the ECG digitally and transmits it wireless to a computer. 2, Using an elastic girth (OrthoHorse) with Velcro, the recorder and wires are fixed within the girth by closing the tissue flap (arrows). 3 and 4, Proper placement of self-adhesive electrodes under the girth (so that they do not fall off during recording) results in good quality recordings from leads I, II, and III.

FIGURE 2 Example of an ECG obtained from the system described in Figure 1. Electrodes are placed as indicated in figure 1 to record three leads in this horse. Leads I and II produce the largest deflections. However, ventricular premature complexes are hard to differentiate from the normal complexes on lead II (*). The difference is more obvious on lead I (arrowheads) but most easily seen on lead III (arrows), which shows the smallest deflections.