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An ectopic beat originating from the ventricles is called a ventricular ectopic beat. Ventricular ectopic complexes (VPCs) are characterised by being wide (more than 70 ms in dogs and more than 40ms in cats) and bizarre, and their T waves are prominent. It is helpful to compare both the QRS and T waves to those of normal sinus rhythms to appreciate those variations. VPCs are also not associated with P waves which can be intermittently present or may be buried within the QRS complexes or the T waves. When two of these ventricular complexes appear together they are name couplets, when three of them triplets and when four or more a ventricular rhythm. Rhythms above 180 beats per minute are called ventricular tachycardia. Those between 60 and 180 in dogs or 120 and 180 in cats are called accelerated idioventricular rhythms and those below 60 in dogs and 120 in cats are idioventricular rhythms. Ventricular rhythms can be caused by cardiac causes (in particular any disease affecting the ventricles) or by extra cardiac causes. Almost any cardiac disease can cause ventricular ectopy but cardiomyopathies, congestive heart failure, cardiac tumours and congenital defects such as subaortic stenosis are often associated with it. Some of the extracardiac causes which can cause ventricular ectopy include: systemic diseases such as SIRS or shock states; abdominal diseases such as splenic masses, pancreatitis or GDV; neurological diseases; diseases causing hypoxia and/or hypoxaemia such as respiratory diseases or anaemia and acid-base or electrolytes imbalances. Three major aspects need to be looked at before treating a ventricular arrhythmia:
1. The complexity of the arrhythmia: How fast? How frequent? Is it unifocal or multifocal? Is there R on T? If fast (above 180-200 bpm), very frequent, multifocal and with R on T it is more likely that antiarrhythmic therapy will be indicated. Accelerated idioventricular rhythms are often caused by systemic disease or hypoxia and very rarely require specific antiarrhythmic therapy (other than treating the underlying disease). Idioventricular rhythm are often escape rhythms (subsidiary pacemakers and life-saving rhythms) which should not be treated with antiarrhythmics.
2. The presence of clinical signs and haemodynamic compromise.
3. The underlying disease: Is the underlying disease transient or persistent/progressive?
The most common antiarrhythmic therapy used include lidocaine (IV), sotalol (PO), mexiletine (PO) and amiodarone (PO). It is however very important to always treat first or at the same time the underlying disease (e.g. CHF or anaemia) as the arrhythmia may disappear or improve markedly when this is carried out first.
