Page 171 - Problem-Based Feline Medicine

10 – THE CAT WITH TACHYCARDIA, BRADYCARDIA OR AN IRREGULAR RHYTHM 163

Pathogenesis which appear similar to P waves, but these can be
distinguished from true P waves because they do not
This arrhythmia results from rapid disorganized atrial
occur in every lead. With atrial flutter, P waves can be
activity “bombarding” the AV node.
identified in all leads with a regular P–P interval.
The heart rate may be normal or increased.
Frequent paroxysmal supraventricular tachycar-
Its presence is usually associated with severe left atrial dia: Usually paroxysmal supraventricular tachycardia
enlargement. is sustained for several beats. These beats have a regu-
lar R–R interval compared to atrial fibrillation where
the R–R interval is always irregular.
Clinical signs
In the majority of patients, clinical signs are related to Treatment
the underlying cardiac disease. The goal is to obtain a heart rate below 180 beats per
Clinical signs related to a fast heart rate (> 280 bpm) minute in the exam room. The heart rate should be
include restlessness, tachypnea, open-mouth breathing, determined by ECG rhythm strip. Several recheck
poor pulse quality and delayed capillary refill time. visits, usually weekly, may be needed for adjustment
of medication to reach the target heart rate.
The onset of atrial fibrillation may be marked by decom-
pensation of the heart disease with pulmonary conges- For cats with underlying dilated cardiomyopathy:
tion. ● Digoxin at 1/4 of 0.125 mg tablet/cat PO every
24–48 hours. Cats should be monitored carefully for
signs of toxicity, and medication stopped if anorexia
Diagnosis or vomiting develop.
For cats with preserved myocardial systolic function:
The heart rate may be normal or increased (Figure 10.2).
● Atenolol at 12.5 mg/cat PO every 12 hours.
There are no visible P waves in any lead. ● Diltiazem at 7.5–15 mg/cat PO every 8 hours.
● Propranolol at 2.5–5 mg/cat PO every 8–12 hours.
Small fluctuations on the baseline (f waves) may be
● Sotalol at 10–20 mg/cat PO every 12 hours.
seen and are not related to the QRS complex.
The ventricular rate is irregularly irregular, and the Prognosis
QRS complex has a normal configuration.
In general, this arrhythmia is associated with end-stage
cardiac disease and with severe left atrial enlarge-
Differential diagnosis ment. It may predispose to the development of throm-
boembolic disease.
Atrial flutter with variable conduction: With atrial
fibrillation the baseline may have some deflections The prognosis for long-term survival is poor.

RHYTHM STRIP: II
50 mm/sec; I cm/mV f f

Figure 10.2. Atrial fibrillation. Note fibrillatory “f” waves.