Friday, March 27, 2015

Three (and a bit) things I learned about ECGs in small animal patients

kitten stethoscope
I've lost count of the number of times my stethoscope is nommed by small animals.

How confident are you in interpreting ECGs? Cardiology specialist Dr Niek Beijerink gave a great talk this week on ECGs for general practitioners and I picked up a few user-friendly tips. ECGs been around forever, in fact since the 19th Century, but they still have the power to freak vets and vet students out.

So here is what I learned:

  1. There are only really three big indications for performing an ECG: bradycardia (in a dog with a heart rate less than 60, or 65 if the dog is very nervous); tachycardia (depending on the anxiety) and irregularly irregular rhythm (except for sinus arrhythmia). In cats an irregular rhythm is always abnormal. Other indications include syncope, although normally dogs with syncope will present with one of the formerly mentioned major indications, e.g. bradycardia.
  2. Ideally dogs should lay in right lateral recumbency because this is how reference ranges for ECGs are made. That said, the colour system of ECGs can be specific to a machine so you need to check the manual of each machine you use before placing electrodes. Cats can be measured in sternal position, but don’t over-interpret small changes. They have smaller complexes in the first place which makes them a bit harder ECG. Now there are apps to obtain an ECG using a smartphone.
  3. Neik analyses ECGS according to a comprehensive checklist. That means that for every ECG he assesses: the quality of the registration (including whether the ECG is for that specific patient), regularity and frequency (assessed in light of the indication, eg tachycardia), the consistency of association between p and qrs (there should always be a p wave before every qrs complex, and there should be a qrs after every p wave). He looks at the height and duration of P waves (for example of the P wave is too high it might indicate right atrial enlargement). He assesses AV conduction (looking at the pq interval), examines the qrs complex (duration, height, configuration, heart axis), the st segment, t wave and qt interval. There is no part of the ECG he ignores.
  4. Assume arrhythmias are either always either problem of impulse formation, or impulse conduction. For example, if animal has bradycardia, it is almost always a disorder of impulse conduction. If it has a tachyarrhythmia, this would be due to a disorder of impulse formation.
  5. Always treat the animal, not the rhythm. In particular, with VPCS, treat the underlying cause. Potential cardiac causes of VPCs include dilated cardiomyopathy, arrythmogenic right ventricular cardiomyopathy, hypertrophic cardiomyopathy, endocarditis, myocarditis, myocardial contusion. Extra-cardiac causes include hypoxemia, anaemia, intoxication (e.g. digoxin), gastric-dilatation volvulus or splenic masses.

Declaration: the webinar was hosted by PAW (Blackmores).