These are referred to as F waves the QRS complexes are normal, and occur at a more normal and regular heart rate, often at a set frequency to the F waves.ĭisturbances of Ventricular Impulse Formation Is seen as a rapid and regular, 'saw toothed' type movement of the baseline, at a rate of 300-500/min. Slower rates are sometimes seen in the giant breed dogs. The ventricular rate in dogs and cats is nearly always fast, as most cases are in congestive heart failure and therefore there is a compensatory sympathetic drive. They may be indistinguishable from baseline artefact. Sometimes fine irregular movements of the baseline are seen as a result of the atrial fibrillation waves-referred to as F waves. In the majority of cases there are no recognisable P waves preceding the QRS complex. Is recognised by an irregular chaotic ventricular rhythm. It is frequently impossible to differentiate atrial tachycardia from a junctional tachycardia.
The P waves are usually inverted and may precede, be superimposed on or follow the QRS complex. In junctional tachycardia an ectopic focus in the AV junction acts as the primary pacemaker. The rhythm is regular unless a multifocal tachycardia is present. This is characterized by a tachycardia where the P wave configuration differs from the sinus P waves. Supraventricular Tachycardia (SVT)-Atrial or Junctional The QRS complexes are narrow upright complexes in lead II and look similar to the sinus complexes. The P waves may be positive, negative or hidden in the QRS complexes. These are supraventricular complexes that occur early and arise from a focus in the atria or the AV node junctional area rather than from the sinus node. Supraventricular Premature Complexes (SVPC) Animals in pain or with pyrexia may also show a persistent sinus tachycardia.ĭisturbances of Supraventricular Impulse Formation Animals with incessant tachycardia may well have underlying congestive heart failure with high sympathetic drive. Sinus tachycardia is probably the most common rhythm detected in small animal cardiac patients due to the excited state of most patients. The recommended protocol is to record an ECG trace, then administer atropine (0.04 mg/kg by subcutaneous injection) and after 30 minutes record a further ECG trace.
If these bradyarrhythmias are genuinely related to high vagal tone, they should be easily abolished by the administration of atropine. It may also be recognised in patients with hypothermia, hyperkalaemia, CNS lesions, or drug related, e.g., digoxin, opioids, beta blockers, calcium channel antagonists. Periods without evidence of any sinus node activity may be prolonged enough to result in syncope. It is usually recognised in dogs with high vagal tone such as brachycephalic dogs or dogs with underlying respiratory disease. Sinus arrest is a period where there is no evidence of atrial activity for a period in excess of the two preceding R-R intervals, and implies that there is a depression in automaticity within the sinus node. This lecture will focus on the identification of arrhythmias and the treatment options. Arrhythmia can be divided into disturbances in impulse formation and impulse conduction which may result in bradyarrhythmias or tachyarrhythmias.
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