Page 221 - Feline Cardiology

226 Section F: Arrhythmias and Other Electrocardiographic Abnormalities

QRS
QRS

P P

purr

Figure 18.10. Artifact mimicking atrial fibrillation/flutter in a cat: ECG manifestation of purring. Intermittent artifact, rather than su-
praventricular tachycardia, is diagnosed (during the segments highlighted by the blue bars) because there is no influence on the heart
rhythm and in several instances a P wave can be seen at the expected P-R interval during the artifact. A true supraventricular tachycardia
producing so many fine deflections due to atrial depolarization instead of these motion artifacts would inevitably conduct on an intermit-
tent, variable basis through the AV node, producing an irregularly irregular R-R interval. The diagnosis is purring artifact in normal sinus
rhythm in this adult male cat 24 hours after relief of urethral obstruction. 25 mm/sec, 0.8 cm/mV.
Arrhythmias QRS

P T

shiver

Figure 18.11. Artifact mimicking atrial fibrillation/flutter in a cat: ECG manifestation of shivering. As for Figure 18.9, a supraventricular
arrhythmia is essentially ruled out by the perfectly regular R-R intervals. 50 mm/sec, 2 cm = 1 mV.

appreciate. Therefore, a cat suspected of having AF but ment to suppress AF impulse generation in the atria is
where uncertainty persists in the ECG diagnosis should not currently available; use of existing medications to
have 1) a multiple-lead (10-lead) ECG, to identify P accomplish this goal would invariably cause toxicosis
waves and thus rule out AF if the P waves are only visible before improvement in the rhythm. Therefore, effective
in some leads and not in lead II, for example; and 2) a treatment in cats with AF, as in the majority of dogs and
vagal maneuver (see above) if the rate is >260 beats/ humans, revolves around rate control: selective modifi-
minute and it is not possible to determine whether irreg- cation of the AV node such that the number of impulses
ularity exists in the R-R intervals because the beats occur transmitted to the ventricles each minute resembles the
so close together. The paper speed of the ECG should be normal heart rate. A cat with AF whose heart rate (ven-
50 mm/sec, and accelerating it further rarely helps clarify tricular response rate) is similar to the expected heart
the diagnosis; the ECG is effectively “stretched” this way rate of a normal cat (e.g., <220 beats/minute in the
but the amount of time between heartbeats is unchanged. exam room) does not require treatment for the AF. An
Performing a 10-lead ECG and using vagal maneuvers “innocent bystander” advantage is sometimes obtained
help to identify P waves and a regular rhythm, respec- when the underlying heart disease requires treatment
tively, and both of these findings are useful for confirm- and AF is also present; the drug used for treating the
ing artifact, rather than AF, since organized atrial activity structural heart disease (e.g., a beta blocker or calcium
and a regular heart rhythm rule out AF. channel blocker for HCM, or digoxin for DCM) may
The goal of treatment of cats with AF is to limit have rate-limiting effects on conduction through the AV
excessively rapid heart rates, but not usually to convert node, which provides a second benefit by reducing an
the AF back to sinus rhythm. Conversion to sinus excessive heart rate. Drugs typically used for treating AF
rhythm is impractical and unlikely to last when sub- in cats include atenolol (6.25 mg PO q 12h initially; may
stantial atrial enlargement exists (Bright et al. 2005), as increase up to 12.5 mg PO q 12h with careful monitor-
it almost always does in cats with AF. Likewise, treat- ing at higher doses to avoid triggering lethargy, inap-