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Electrocardiography 1097

• If the reason for using cardiac monitoring
is the occurrence of sporadic clinical signs,
VetBooks.ir indicated in addition to the ECG:
a complete medical evaluation is usually
○ CBC, serum biochemistry, urinalysis
+/− urine culture: all cases; hypoglycemia,
hypocalcemia (p. 515), urinary tract
infection (p. 232), acid-base/metabolic
disorders
○ Serum preprandial and postprandial bile
acids (if consistent with case): hepatic
encephalopathy (p. 440)
○ Thoracic radiographs, echocardiogram
(p. 1094): all cases; assessment of cardiac
structure, presence or absence of conges-
tive heart failure Procedures and Techniques
○ Troponin-I (p. 1389), tick panel, Chagas
(if consistent with case): myocarditis (p.
675)
ELECTROCARDIOGRAPHY Patient is gently restrained in right lateral recumbency, with the legs perpendicular
Possible Complications and to the body. Patient is placed on a mat for insulation to reduce electrical interference. Standard limb leads are
Common Errors to Avoid attached in addition to two precordial leads.
• Poor electrode/lead contact with skin:
avoided by applying sufficient isopropyl
alcohol to the skin at the location of lead
contact, clipping fur if adhesive electrode green = right hindlimb, red = left hindlimb. ECG Clip/Electrode Placement for
patches applied Precordial leads may also be attached. Standard Limb Leads (I, II, III, aVR,
• Motion artifact (can mimic abnormal cardiac • Alcohol or conducting gel should be applied aVL, aVF)
activity, leading to misdiagnosis): avoided where leads are attached to patient (unless
by adequate patient restraint (+/− sedation leads attached to adhesive electrode pads). Electrode Placement
if safe and necessary); apply leads to distal • A standard ECG includes tracings from all RA, white Right forelimb, clip to skin
limbs to minimize respiratory motion artifact six limb leads (I, II, III, avR, aVL, aVF). just proximal to the olecranon
• Electrical interference: avoided by placing Additional information may be gained (caudal triceps region)
patient on nonconductive surface, adjusting from precordial lead tracings. Generally, LA, black Left forelimb, clip to skin just
filter setting on ECG machine to eliminate the ECG is collected and monitored for 3 proximal to olecranon (caudal
60-Hz cycle interference, avoid wire-to-wire minutes for overt abnormalities/abnormal triceps region)
and/or clip-to-clip contact complexes. ECG settings should be noted
• Purring/shaking artifact: alcohol-soaked and adjusted as needed (e.g., paper speed of RL, green Right hindlimb, clip to skin just
proximal to the stifle (cranial
gauze in front of cat’s nose, fear-free/calming 25 or 50 mm/sec); sensitivity of 10 mm/mV thigh); ground wire
techniques for shaking/nervous patients is standard, but half sensitivity (5 mm/mV)
+/− sedation if safe and necessary may be necessary when large QRS complexes LL, red Left hindlimb, clip to skin just
• Multiple leads should be evaluated rather than present (e.g., tall R waves, deep S waves, proximal to the stifle (cranial
thigh)
just one lead: lead II does not always provide or ventricular premature complexes). The
clearest deflections/waves, and assessment of tracing can be evaluated in more detail to
multiple leads provides various viewpoints perform specific interval and deflection
around the heart to more thoroughly evaluate measurements (e.g., PR interval, R-wave monitoring (up to 10 months). Devices are
directionality of electrical activity, as well as height, QRS duration) after completion of very small (size of a USB jump drive), and
artifact the procedure. Measurements ideally should implantation is achieved with a subcutaneous
• Cutaneous adhesive pads should be used be performed on 50-mm/sec paper speed for pocket. Devices are available from Canpac-
for prolonged ECG monitoring (e.g., under accuracy. ers and relatively inexpensive. Access to a
general anesthesia, hospitalized patients) to Medtronic programmer is necessary, however,
avoid damage to the skin from prolonged Postprocedure to retrieve the stored information.
attachment of lead clips. Clips are carefully removed from the patient • Smart phone ECG application: smartphone
before release of restraint, or adhesive pads are case with electrodes can be purchased and used
Procedure removed after monitoring is complete. with the associated app (www.alivecor.com);
• Patient should be placed in right lateral allows owners to collect ECG tracing at home
recumbency. Other positions (sternal, sitting, Alternatives and Their Relative and transmit electronic PDF of ECG to
standing) are also acceptable, but determina- Merits veterinarian by email.
tion of mean electrical axis and criteria for • Telemetry: for prolonged ECG monitor-
chamber enlargement is applicable only if ing (e.g., patients admitted to hospital or AUTHORS: Ashley E. Jones, DVM, DACVIM; Amara H.
ECG performed with standard positioning. monitoring after anesthesia) Estrada, DVM, DACVIM
• Typically at least two people are required to • Holter monitor: 24-hour ECG used for EDITORS: Leah A. Cohn, DVM, PhD, DACVIM; Mark S.
perform an ECG: an assistant to restrain the screening occurrence of infrequent arrhyth- Thompson, DVM, DABVP
patient and a clinician to attach the leads mias, for antiarrhythmic therapy monitoring
and interpret the tracing. • Event monitor: for long-term (days to
• Leads are attached to skin of distal limbs months) monitoring
according to color/label. Usually, white • Implantable event monitor (e.g., Reveal Plus
= right forelimb, black = left forelimb, [Medtronics]): allows an extended period of

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