Electrocardiography is an integral part of the cardiological exam. It is the only way to determine heart rhythm accurately
and to determine if there are any conduction abnormalities. This is also the most useful part of an ECG. ECGs can do other
things however, these are not nearly as important.
An ECG is a recording of the electrical activity of the heart recorded on the surface of the body (or from the esophagus).
Standard lead systems have been developed, these help determine the orientation of the depolarizing forces, an indirect indicator
of the position of the heart in the chest cavity. These lead systems are however not needed to determine rhythm, you could
in theory record the ECG from the fingertips if you have to.
1. How can an ECG be recorded: A standard lead system can be used an electrodes attached to the limbs. This does require
that the patient be in right lateral recumbency. This must be done if amplitude measurements are to be made (only in lead
II). Alternatively a direct chest lead system can be used for rhythm diagnosis. Telemetry, holter monitors (24 hour ambulatory
ECG) and cardiac event recorders (push a button and it records ECG immediately before and after the button is pushed) are
other specialized ECG forms.
2. What can an ECG do extremely well: Only the ECG can determine rhythm or conduction abnormalities.
3. What can an ECG do well: The ECG can be helpful in evaluating for heart enlargement. These changes are however not
specific nor sensitive. It is more sensitive in cats because there are less confounding breed differences. The ECG is also
more helpful with certain congenital heart diseases. It can be helpful for diagnosing pericardial effusion and hyperkalemia.
4. What can an ECG not do: It cannot give a definitive answer regarding heart size, imaging studies are needed. ECGs
also do not reflect the mechanical strength of the heart, an ECG can be normal and no pulse may be present.
5. What are the indications for an ECG: arrhythmia on auscultation, syncope, heart murmur, pre-, intra- and postop monitoring,
dyspnea, cyanosis, drug monitoring (digoxin, beta blocker, tricyclic antidepressants), emergency cases (trauma, GDV, urethral
obstruction, hyperkalemia suspect), periocardiocentesis (VPCs indicate the needle is tickling the heart), certain breeds (doberman,
boxer), unexplained brady- or tachycardia.