Cardio. Arrhyth. Chap 48.

Question 1

ventricular escape rhythm (idioventricular rhythm)
accelerated idioventricular rhythm
ventricular tachycardia

Answer 1

rate of about 30 to 40 beats/min (60 to 130 b/min in cats)
rate >40 <160 dogs
>160bpm - upper limit of normal sinus >3 beats

Question 2

define VT

Answer 2

Purkinje cells or any excitable ventricular myocyte = ventricular rhythm as three or more consecutive ventricular beats occurring at a rate faster than conventional upper limit for normal sinus rhythm

Question 3

Three arrhythmogenic mechanisms:

Answer 3

enhanced automaticity
triggered activity
reentry

Question 4

nonsustained vs. sustained VT:

Answer 4

nonsustained < 30 seconds

sustained if it lasts longer

Question 5

incessant VT vs VT storm:

Answer 5

recurrent episodes of sustained VT in 24-hr
VT storm is a life-threatening emergency
synonyms

Question 6

Dx VT:
QRS > __:
QRS. followed by ___:

Answer 6

6-lead surface ECG right lateral recumbency
broad QRS tachycardia
wider than 0.06 second in dogs
0.04 second in cat

large T wave, directed opposite to the QRS deflection

Question 7

challenge to ddx:

Answer 7

differentiate VT from broad complex SVT

because of structural BBB, a functional or rate-related BBB, or finally an accessory atrioventricular pathway

Question 8

three most reliable diagnostic criteria of VT:

Answer 8

1. AV dissociation
2. fusion beats
3. capture beats

Question 9

AV dissociation decribe and draw:

Answer 9

P waves are occasionally seen on the ECG tracing but are not related to ventricular complexes

these P waves reflect atrial activity independently from
the ventricle

Question 10

fusion beats

Answer 10

summation of a ventricular impulse and a simultaneous supraventricular impulse

= QRS complex of intermediate morphology and preceeded by a P wave

Question 11

capture beat

Answer 11

supraventricular impulse conducting through the
normal conduction pathways to the ventricle during an episode of VT or AIVR

occurs earlier than expected and is narrow if the conduction system is intact

Question 12

VT vs a-fib/SVT:

Answer 12

regularity of the rhythm - less accurate criterion because VT can be slightly irregular but when the RR interval varies by >100 msec suggestive of atrial fibrillation

vagal manuever

clinical picture (Boxer/Doberman)

p-waves

Question 13

When in doubt, why treat SVT as VT?

Answer 13

• managing SVT as VT is usually less dangerous
• drugs used to stop SVT (i.e., CCB & β-blockers) do not interrupt VT but do worsen hypotension with
  their vasodilatory or negative inotropic effects

Question 14

Dx VT on ECG, next step is to ddx:
noncardiac (4):
cardiac (2):

Answer 14

noncardiac:
1. hypoxemia
2. electrolyte imbalances (hypokalemia)
3. acid-base disorders
4. drugs

cardiac:
1. ARVC arrhythmogenic cardiomyopathy in boxers
2. DCM Doberman Pinschers

Question 15

Most common cause of noncardiac and MoA:

Answer 15

Hypokalemia 
-increases phase 4 depolarization
-increasing spontaneous automaticity
-prolongs AP duration 
= promotes arrhythmias from triggered activity

Question 16

MoA Digoxin arrhythmia increase risk with what e-:

Answer 16

digoxin competes with potassium on its
receptors (Na/K ATPase)
-hypokalemia increases the risk of digoxin toxicity
-hypomagnesemia bc cofactor sodium-potassium ATP

Question 17

MoA drug induced prolonged QT segment:
risk of arrhythmia via what mechanism:
and examples:

Answer 17

• reflects prolongation of cardiac membrane repolarization
• risk of ventricular arrhythmia from triggered activity
• procainamide and sotalol
• cisapride, erythromycin

Question 18

Tx - first ID these underling causes and correct via:

Answer 18

correct e-, suppl. O2, removed drugs

Question 19

If R/O non-cardiac, next dx:

Cardiac ddx:

Answer 19

Echo
occasionly w cardiac tumors, myocarditis, endocarditis, and ischemia

DCM, ARVC

Question 20

Breed prevelance in DCM
Newfoundl.
Doberman

Answer 20

21%
16%
92%

Question 21

Dobermans
occult stage risk or death
over stage risk of death

Answer 21

occult stage of the disease no CS but echo indicators of left ventricular dysfunction - approximately 30%

It can last 2 to 4 years.

In the overt stage - approx. 30% to 50%

Question 22

Dober. BBB morphology:

indicating originating in ____ ventricle:

Answer 22

right bundle branch morphology in lead II

left ventricle

Question 23

GSH

Answer 23

inherited ventricular arrhythmia has been identified in some German Shepherds
propensity for sudden death until 18 months of age
polymorphic, rapid (>300 beats/min), nonsustained, and usually preceded by a pause

Question 24

Boxer:
BBB:
Ectopy originating in:

Answer 24

left BBB

right ventricle

Question 25

Decision to treat:

Answer 25

polymorphic, >180, R-on-T, CV collapse

Question 26

MoA of R-on-T

Answer 26

superimposition of an ectopic beat on the T wave of the “vulnerable period”
represent an increased risk for VT and sudden death from ventricular fibrillation

Question 27

first line tx:
MoA:
Why first line:
Cats:

Answer 27

Lidocaine
Fast Na channel blocker - phase 0 of AP, Class 1b
better on rapid VTs and in normokalemic animals
-B-blocker preferred

Question 28

If lidocaine dose not work:

-ve:

Answer 28

Procainamide class 1a
Procainamide is used intravenously for VTs that do not respond to lidocaine (bolus of 10 to 15 mg/kg)CRI 25 to 50 mcg/kg/min 

• rapid IV can cause hypotension
• long-term management of VT can be attempted with oral procainamide at 10 to 20 mg/kg q6h

Question 29

B-blockers and VT:

risk:

Answer 29

Esmolol is a short-acting β-blocker that can
help control sympathetically driven VTs such as those associated w pheochromocytoma or thyrotoxic dz cats

negative inotropic effects may be too pronounced in some patients = cardiovascular collapse

Propranolol, a nonselective β-blocker, is the preferred β-blocker for the treatment of VT storm human

Question 30

Sotalol:

Amiodarone:

Answer 30

Sotalol is an oral medication that is very effective at controlling VT

it is the main antiarrhythmic drug for longterm management of VT, especially in Boxers with arrhythmogenic cardiomyopathy

author often administers sotalol at 1 to 2 mg/kg PO to
restore sinus rhythm in dogs with VT refractory to lidocaine and procainamide

Amiodarone at MSU
bolus of 5 mg/kg over 10 minutes

Question 31

Magnesium sultate:
MoA:

Digitalis glycosides and hypomagnesmia both inhibit:
and increase intracellular ____ levels:

Digoxin also increases urinary excretion of:

Answer 31

anecdotal IV magnesium sulfate as an adjunct

• have evaluated magnesium therapy in reversing prolonged QT syndrome (cofactor)
• there are no studies evaluating the efficacy of magnesium therapy in dogs with spontaneously
• human reports that it aids in therapeutic drug overdoses, but it is not considered mainstream antiarrhythmic therapy

sodium–potassium ATPase
calcium

magnesium

A variety of arrhythmias can develop with digitalis toxicity, and these can be responsive to magnesium sulfate administration

Question 32

Other treatments

Answer 32

Anesthesia/sedation to decrease high sympathetic tone

Electrical therapies - Rapid pacing is indicated to overdrive suppress some ventricular arrhythmias

Finally - arrhythmia can be terminated via synchronized electrical cardioversion or defibrillation