Page 170 - Problem-Based Feline Medicine

162 PART 3 CAT WITH SIGNS OF HEART DISEASE

than the tachycardia, and include a heart mumur, dysp- Treatment
nea, weakness, collapse and lameness, paralysis or pare-
If the patient is symptomatic (hypotension, cardiogenic
sis from systemic thromboembolism.
shock, collapse) for the arrhythmia, then treatment is
Clinical signs related to a fast heart rate (> 280 bpm) required. The following drugs can be used in succes-
include restlessness, tachypnea, open-mouth breathing, sion and are written in order of preference if the previ-
poor pulse quality and delayed capillary refill time. ous drug is not effective.
● Diltiazem at 0.1–0.3 mg/kg IV slow bolus over
3–5 minutes. The dose can be repeated in 5–10
Diagnosis minutes if sustained SVT. After IV bolus an intra-
venous constant rate infusion can be started at
The diagnosis is based on physical examination and an
5–20 μg/kg/min. Diltiazem is compatible with any
electrocardiogram.
type of IV fluids.
The heart rate is above 220 bpm. ● Esmolol at 250–500 μg/kg IV bolus given slowly
over 1 minute. The bolus can be followed with
The cardiac rhythm is regular.
a constant rate infusion at 50–200 μg/kg/min.
The QRS complex morphology is normal. Esmolol is compatible with 5% dextrose.
● Propranolol at 20 μg/kg IV slow bolus over
There is a P wave for every QRS complex, but the P
5 minutes. Propranolol can be given up to a total
wave morphology may or may not be different from
dose of 100 μg/kg in repeated boluses.
normal sinus beats.
If the patient is not symptomatic for the arrhythmia:
P waves may be “buried” in the S–T segment.
● Atenolol at 6.25–12.5 mg/cat PO every 12 hours.
The arrhythmia may be sustained or occur in parox- ● Diltiazem at 7.5–15 mg/cat PO every 8 hours.
ysms. ● Propranolol at 2.5–5 mg/cat PO every 8–12 hours.
● Sotalol at 10–20 mg/cat PO every 12 hours.
The changes in the heart rate are abrupt. The
arrhythmia may terminate spontaneously with a
sudden decrease in heart rate.
Prognosis
The QRS complex may be slightly aberrant in the
beginning of the paroxysm of tachycardia. The prognosis depends on the underlying etiology.
The QRS complex may alter its configuration (electri- In general, the presence of this arrhythmia suggests
cal alternans) in the first few seconds of the run of advanced underlying cardiac disease.
tachycardia.
In cases where the etiology is due to the existence of a
by-pass tract, the cat may have a good prognosis, pro-
Differential diagnosis viding there is good control of the tachycardia.

Sinus tachycardia may look identical to supraventricu-
lar tachycardia sinus on the ECG. Excessive heart rate
(greater than 250 bpm) is more likely to be supraventric- ATRIAL FIBRILLATION*
ular tachycardia. Supraventricular tachycardia may have
abnormal P wave morphology or lack P waves compared Classical signs
to sinus tachycardia where P waves are normal.
● Fast and irregularly irregular variable heart
Motion or electrical artifact can usually be resolved rate.
by improved ECG recording technique: repositioning ● Strong precordial impulse.
the electrodes, moistening the skin with alcohol, posi- ● Loud and variable S1 heart sound.
tioning the cat on a non-metal table isolated from other ● Weakness/collapse (rare).
electrical devices.