Page 64 - Basic Monitoring in Canine and Feline Emergency Patients

Because variants of sinus rhythm (sinus arrhyth- compared to normal sinus complexes; (ii) the pres-
mia, sinus bradycardia, sinus tachycardia) almost ence of a large T wave of opposite polarity; and (iii)
VetBooks.ir always occur as a physiologic response to changes the absence of a preceding P wave. Ventricular ectopy
can be caused by abnormal automaticity (ectopic
in autonomic tone, these ‘arrhythmias’ rarely require
directed treatment. Rather, the underlying cause of
sinus tachycardia or bradycardia (see Table 3.2) activity) in ventricular myocytes or re-entrant loops
of electrical activity within the ventricles. A number
should be identified and treated if needed. of terms are used to designate how frequently ven-
Persistent sinus tachycardia that occurs secondary tricular ectopic beats occur. A single ventricular
to drug toxicity or autonomic imbalance is typic- ectopic beat that occurs before the next expected
ally treated with a β-blocker (such as oral atenolol sinus beat is called a single (or isolated) ventricu-
or IV short-acting esmolol; see Table 3.6) to dir- lar premature complex. Two VPCs in a row is called
ectly counteract SNS overstimulation and slow sinus a ventricular couplet; three VPCs in a row is
rate. Persistent sinus bradycardia causing hypoten- called a ventricular triplet; and more than three
sion (e.g. during general anesthesia) can be treated VPCs in succession is termed ventricular tachycar-
with an anticholinergic (atropine, glycopyrrolate; dia (VT) (see Fig. 3.9). Periods of VT alternating
see Table 3.6). with sinus rhythm are often called ‘runs’ or ‘parox-
ysms’ of VT. Ventricular ectopy (the umbrella term
Common tachyarrhythmias in small animals for these arrhythmias) can occur in patients with
structural heart disease (and is particularly com-
Ventricular tachyarrhythmias
mon in dogs with dilated cardiomyopathy or
A ventricular ectopic complex is recognized electrocar- arrhythmogenic right ventricular cardiomyopathy)
diographically by (i) wide, bizarre QRS morphology or cardiac trauma. However, ventricular ectopy can

Fig. 3.7. Lead II ECG (25 mm/s, 10 mm/mV) showing sinus arrhythmia / sinus bradycardia. The heart rate is
approximately 60 bpm. The rhythm is irregular, with greater than 10% variation in R–R interval between beats.
Normal P–QRS–T complexes are identifiable for each beat.

Fig. 3.8. Lead II ECG (25 mm/s, 10 mm/mV) showing sinus tachycardia. The heart rate is approximately 180 bpm.
The rhythm is regular, and normal P–QRS–T complexes are identifiable for each beat.

56 J.L. Ward