Page 56 - Rapid Review of ECG Interpretation in Small Animal Practice, 2nd Edition

Holter Monitoring

Ventricular arrhythmias are identified by a wide- Table 5.2 Ventricular premature beat counts in
complex QRS, while supraventricular beats are
VetBooks.ir defined by their degree of prematurity. Manual normal dogs VPCs/24 h
Breed
review of automated analyses is needed to
identify wide complex QRS complexes during Beagles <9
sinus rhythm due to abnormal ventricular Large breed dogs 0–24
conduction (i.e., bundle branch block). The Boxers <91
Holter report should provide a total abnormal Doberman Pinschers <50
beat count and quantify whether or not Salukis 0–4
there is complex ventricular ectopy (such as
couplets, triplets, or ventricular tachycardia),
as well as the maximum number of consecutive
ventricular beats and maximum heart rate of ANTIARRHYTHMIC TREATMENT
the tachycardia episodes. Occasional ventricular ASSESSMENT UTILIZING 24-HOUR
escape beats during periods of low heart rate HOLTER DATA
are a normal finding in dogs. Up to 50 single Ideally, antiarrhythmic therapy efficacy should be
ventricular premature beats/24 h can occur in assessed by comparing a pre-treatment and post-
normal dogs other than Boxers. However, even treatment (1–2 weeks after initiating medical
if the total number of ventricular premature therapy) Holter recording. In cases where ventricular
beats is within normal limits, presence of tachycardia is observed on in-hospital ECGs or very
complex ventricular ectopy such as couplets, frequent fainting, a pre-treatment Holter may not
triplets, or ventricular tachycardia is abnormal. be acquired so as to avoid delay in the initiation of
Significant day-to-day variation in the frequency therapy. However, the absence of pre-treatment Holter
and complexity of ventricular ectopy occurs in data makes it difficult to fully assess the response to
dogs, which is why longer recording periods therapy. Comparing pre-treatment and post-treatment
(i.e., 7-day or loop recorders) are sometimes Holter recordings might also reveal potential
indicated. Normal Holter findings in dogs based proarrhythmic drug effects and allow evaluation of
on previous studies are listed in Tables 5.1 treatment efficacy. Because of considerable day-to-
and 5.2. day variability in VPC number, an adequate treatment
response should yield at least an 80% reduction in
VPC number and a reduction in the complexity of the
Table 5.1 Normal 24-hour Holter ECG findings arrhythmia on the post-treatment Holter.
in dogs Specifically, identification of frequent ventricular
ectopy in an adult Boxer or Doberman Pinscher is
Parameters 24-hour Holter ECG findings strongly suggestive of a diagnosis of arrhythmogenic
Heart rhythm Sinus and sinus arrhythmia right ventricular cardiomyopathy (ARVC) or dilated
Mean 24-hour 66 (52–86) bpm cardiomyopathy, respectively, particularly if there is
heart rate (HR)
Minimum 38 (29–52) bpm significant complexity (couplets, triplets, bigeminy,
24-hour HR or ventricular tachycardia) in the absence of other
Maximum 171 (130–240) bpm; underlying systemic or cardiac disease that could
24-hour HR during periods of intense cause ventricular arrhythmias.
exercise/excitement sinus Rate control for dogs with chronic atrial fibrillation
tachycardia may briefly is also best assessed using 24-hour Holter recordings
reach instantaneous rates in the home environment, as in-hospital ECGs tend to
>300 bpm overestimate the ventricular rate of dogs with atrial
Sinus pauses 4–6 seconds at rest fibrillation. Sympathetic stimulation from the stress of
Escape beats Occasional during low heart being in a hospital setting and dog handling for ECG
rates
2nd AVB Rare during periods of low acquisition produce markedly elevated heart rates as
heart rate compared to 24-hour-average heart rates recorded by
Ventricular Uncommon, 0–91 Holter in a familiar setting, making in-hospital ECGs
premature beats (see Table 5.2) of limited value for interpretation of drug efficacy in
this arrhythmia.
Abbreviation: AVB, atrioventricular block

43