Page 2069 - Cote clinical veterinary advisor dogs and cats 4th

1034 Ventricular Arrhythmias

Clinically overt: Differential Diagnosis • Abdominal imaging: if there is suspicion of
• Wide range of presentations, from clinically • VPCs can occur in many situations and an abdominal problem or a primary cause
VetBooks.ir to profoundly weak and hemodynamically disorder. They can be seen in normal animals • Arterial blood gas (ABG) analysis: if acid-base
for the arrhythmia is not found
normal and alert if arrhythmia is intermittent
do not automatically equate to a cardiac
in low numbers (<50/24 hours). They are
collapsed with very rapid, sustained VT
or oxygenation abnormalities are suspected
• Regularity or irregularity and pulse deficit
as for incidental finding (see above) very commonly associated with noncardiac TREATMENT
disease, possibly secondary to myocardial
ischemia, electrolyte abnormalities, or other
Common Causes of Ventricular factors surrounding the underlying disease. Treatment Overview
Arrhythmias • Physical exam (irregular cardiac rhythm) • Control arrhythmia to such a degree that
○ Supraventricular premature beats, marked adequate organ perfusion is present and there
Hypokalemia a,b respiratory sinus arrhythmia is a resolution or control of any arrhythmia-
Hypoxemia (e.g., due to cardiogenic pulmonary
edema, pleural effusion, primary lung disease) a • ECG (wide and bizarre QRS-T complexes) related clinical signs (e.g., syncope).
Cardiomyopathy ○ Right or left bundle branch block • Treatment decisions should be made based
Gastric dilation/volvulus a ○ Ventricular escape rhythm on whether the patient is experiencing or
Traumatic myocarditis/hit by car ○ Right ventricular enlargement (if QRS will experience hemodynamic compromise
Abdominal mass, especially splenic or hepatic a predominantly negative in lead II) due to the arrhythmia. The goal is to treat
Advanced valvular heart disease ○ Motion artifact the patient, not the ECG.
Hypomagnesemia a,b ○ Accelerated idioventricular rhythm • The goal is not to abolish every VPC because
Acidosis a (ventricular rhythm at a rate of 120-170 overzealous treatment of arrhythmias may
Intoxication (digitalis; oleander, foxglove, lily beats/min). This is a fancy term for be detrimental.
a
of the valley, azalea, and yew plants; many
over-the-counter, prescription, or illicit drugs) slow VT, but it is an appropriate name Acute General Treatment
because a ventricular myocyte is firing as
a Potentially correctable/curable. a pacemaker cell at an accelerated rate. A treatment algorithm is provided on p. 1457.
b Presence may make ventricular antiarrhythmic drugs such as • First, determine if the arrhythmia is a
lidocaine, procainamide, and mexiletine ineffective. Initial Database ventricular arrhythmia (VPC, VT) by ruling
ECG (p. 1096) remains the gold standard for out common impostors (see Differential
Etiology and Pathophysiology diagnosis of cardiac arrhythmias. Criteria for Diagnosis above).
• Enhanced or abnormal automaticity, ventricular arrhythmias: • Second, identify and address any relevant
microreentry, and triggered activity (early or • VPC is substantially different from normal underlying causes.
delayed after depolarizations) are mechanisms sinus QRS complexes. • Third, determine if there are overt clinical
that underlie ventricular arrhythmias. ○ Wide and bizarre QRS shape occurs signs associated with the ventricular arrhyth-
• These mechanisms can be activated or because the impulse originates below the mia (e.g., syncope). If so, antiarrhythmic
potentiated by systemic disturbances such bundle of His and therefore cannot take treatment is warranted.
as those previously listed (see Associated advantage of the specialized conduction • Fourth, if the ventricular arrhythmia is
Disorders above). system. It must travel through the ventricu- sustained at a rapid rate (>180 beats/min
• The result is one or more spontaneous electrical lar myocardium from muscle cell to muscle in large-breed dogs, > 220 beats/min in
depolarizations originating prematurely in the cell. This is slow and produces a wide, small-breed dogs, > 260 beats/min in cats),
ventricles. The prematurity is manifested on the bizarre complex. QRS complexes can be antiarrhythmic treatment is indicated.
ECG as a shorter R-R interval. The ventricular positive in lead II or negative, depending • Medications
origin results in a QRS complex that is of a on the site of origin in the ventricle. ○ Lidocaine 1-2 mg/kg (dog) or 0.25-1 mg/
different shape from a sinus QRS complex. ○ VPC occurs prematurely. The R-R interval kg (cat) IV bolus (can repeat up to three
• A greater degree of prematurity of VPCs (or from the preceding normal sinus beat times in 10-15 minutes); can be followed
more rapid VT) results in reduced diastolic to the VPC is shorter than the interval with IV constant-rate infusion (CRI) at
filling time before contraction and ultimately between two normal sinus beats. 40-80 mcg/kg/min (dog) or 10-20 mcg/
a higher probability of clinical signs or ○ Large, bizarre T wave occurs because kg/min (cat)
hemodynamic deterioration (e.g., poor depolarization is abnormal; repolarization ■ To make CRI of lidocaine: withdraw
pulse, cerebral hypoperfusion) compared is also abnormal. 25 mL from a 500-mL bag of crys-
with slower ventricular arrhythmias. ○ P waves continue to occur regularly during talloid fluid (e.g., lactated Ringer’s
• Accelerated idioventricular rhythms are seen ventricular arrhythmias, but they are not solution) and replace with 25 mL of
commonly in hospitalized patients in associa- related to VPCs and often are lost within 2% lidocaine. Concentration in bag is
tion with noncardiac diseases (e.g., GDV the VPCs. 1000 mcg/mL. Administer IV at usual
surgery, splenic disease, immune-mediated fluid maintenance rate (66 mL/kg/
hemolytic anemia, pancreatitis, post trauma, Advanced or Confirmatory Testing day) assuming congestive heart failure
neurologic disease). They are typically benign, • A 10- or 12-lead ECG: improved visual- (CHF) is not present. Infusion at this
the rate is not rapid, and they usually do not ization of certain features of ventricular rate will be 50 mcg/kg/min.
require therapy. arrhythmias (e.g., better ability to see P ○ Procainamide 6-15 mg/kg (dog) or
waves not associated with the wide, bizarre 1-2 mg/kg (cat) slow IV bolus; may follow
DIAGNOSIS QRS complexes of VPCs) with IV CRI at 25-50 (dog) or 10-20
• CBC, serum biochemistry profile, urinalysis: (cat) mcg/kg/min. Usually administered
Diagnostic Overview especially to assess systemic proarrhythmic if lidocaine was ineffective despite normal
Ventricular arrhythmias can be suspected on abnormalities such as hypokalemia electrolyte status, but both may be given
history (syncope), physical exam (premature • Thoracic radiographs: particularly if suspicion together
beats, pulse deficits), and ECG (classically, wide of primary cardiac disease, hypoxemia, or • In patients who do not convert with IV
and bizarre QRS complexes occurring prema- thoracic trauma lidocaine or procainamide, it is important
turely). Careful inspection of the ECG allows • Echocardiogram (p. 1094): if a primary to assess for any electrolyte abnormalities,
differentiation from other similar-appearing but cardiac problem is suspected or no other particularly potassium, because antiarrhyth-
clinically different ECG deflections. cause is identified mic agents are less effective when there is

www.ExpertConsult.com