Cardio.Chap 46 Bradyarrhy

Question 1

Summary:
Sinus bradycardia is usually secondary:
Bradyarrhythmias are more common in:
Most common requiring tx.:
Atril standstilllook for:
Medical management of bradyarrhythmias is:

Answer 1

systemic disease causing high vagal tone
dogs than cats
third-degree AV and sick sinus syndrome
hyperkalemia
rarely successful

Question 2

Bradyarrhythmias are defined as

Answer 2

heart rate < 60 beats/min in dogs, 100 beats/min in cats associated with CS, such as lethargy, decreased appetite, exercise intolerance, CHF, and syncope

Question 3

pauses may extend beyond ____ lead to syncopy

Answer 3

6-8s

Question 4

Conduction disturbances include:

Answer 4

BBB, first-, second-, and third-degree atrioventricular

Question 5

marked vagotonia … what happens to P-waves

Answer 5

wandering pacemaker, which corresponds to a variation in the amplitude of the P wave in relation to the respiratory cycle

Question 6

Sinus Node Dysfunction
Sinus arrest:
sinus block:

Answer 6

Sinus arrest - is identified as a prolonged pause with no atrial activation or P wave on the ECG
Sinus block - which describes the failure of an impulse to exit the sinus node, cannot be differentiated from sinus arrest on a surface ECG

Question 7

Sick sinus syndrome

opioids and SSS

characterized by

breeds

Answer 7

-disease of the conduction system characterized by periods of normal sinus rhythm or sinus bradycardia, interspersed with long sinus arrest that can last up to 10 or 12 seconds because junctional and ventricular pacemakers fail to initiate escape beats

• sedatives results in a prolongation of periods
• while awake ok, but GA hemodynamically unstable

paroxysmal atrial tachycardia followed by a temporary failure of the sinus rhythm to resume when the tachycardia abruptly terminates

corresponds to an exaggeration of a normal physiologic response of the sinus node to the effect of a tachyarrhythmia, a mechanism known as overdrive suppression

-Older Miniature Schnauzers and Terrier breeds are more commonly affected with sick sinus syndrome

Question 8

AV 1

causes

Answer 8

PR interval prolonged: >130 msec dogs, PR >90 msec cats
results from AV node

fibrosis, increased vagal tone, or drugs that delay AV node conduction, including digoxin, calcium channel blockers, and β-blockers

Question 9

AV 2 - high grade

Answer 9

second-degree AV block is said to be high grade when more atrial impulses fail to be conducted to the ventricles than are conducted

Question 10

Wenckebach’s phenomenon

causes:

Answer 10

Mobitz type I second-degree AV block is characterized by a progressive increase in the PR interval duration ending by a blocked P wave

AV node fibrosis and a progressive increase
in vagal tone

This form of AV block is usually benign and does not
require specific treatment

Question 11

Mobitz type II

Answer 11

unexpected occurrence of blocked P waves
PR intervals before and after blocked P waves are identical

QRS complexes of conducted beats are usually wide because the area of block is below the His bundle, causing bundle branch blocks and intraventricular conduction delays

This form of block is more likely to worsen and result in clinical signs.

Question 12

ddx Mobitz I vs II

Answer 12

atropine 0.04 mg/kg IV
type I usually improves after atropine
type II is unchanged or worsens.

Question 13

AV III

Causes

Answer 13

displays independent atrial and ventricular activities

atrial rate, under adrenergic tone, is elevated
electrical activation of the ventricles is dependent on an escape rhythm beyond the site of block

QRS complexes are wide and bizarre at rates around 20 to 60 beats/min in dogs and 60 to 120 beats/min in cats

myocardial fibrosis, inflammation or infiltration, and potentially drug toxicity (calcium channel blockers,
β-blockers, or digoxin)

Age-related fibrodegenerative disease is the most common cause of AV block in dogs

Question 14

Atrial standstill

Answer 14

defined by a lack of visible atrial electrical activity
on the surface ECG

temporary or persistent

persistent atrial standstill is a rare disease that seems more prevalent in English Springer Spaniels

P waves with a regular ventricular or AV nodal escape
rhythm, at rates of 20 to 60 beats/min in dogs

Hyperkalemia is a common cause of temporary atrial standstill - above 5.5 to 6 mmol/L

Question 15

Tx mx:

Answer 15

Terbutaline (0.2 mg/kg orally q8-12h, 0.01 mg/kg IV) is a selective β2 agonist commonly used as a bronchodilator.

Aminophylline (10 mg/kg twice orally q12h, or 10 mg/kg IV) is a phosphodiesterase inhibitor and bronchodilator with mild chronotropic effect.

Question 16

Tx if mx. fails:

Transcutaneous pacing

Answer 16

Pacing electrodes are within adhesive pads applied to clipped skin at the level of the third to fifth costrochondral junction

thorax can be bandaged to ensure good contact if the patient is not anesthetized

ECG is recorded by the pads or via standard limb leads. The pacing rate is programmed, and the pads sense the intrinsic cardiac rhythm and deliver an impulse if necessary

sensitivity adjusted until intrinsic QRS sensed
current (in mA) should be gradually increased until ventricular capture recognized by the appearance of wide QRS complexes on the ECG in addition to palpation of associated femoral pulses

Question 17

Temporary transvenous pacemakers

leads:

Vein:

Describe technique:

Answer 17

lead placed in the right side of the heart, generally the right ventricle, and connected to a generator external to the patient

bipolar, 100 to 110 cm in length and 4 to 6 Fr in diameter

(left leave right for permanent) jugular, saphenous, or femoral vein can be used depending on the size

vascular introducer sheath that is large enough to accommodate the pacing lead is secured in the vein via Seldinger’s technique or via a cutdown

lead is then advanced into the right ventricular apex and attached to the generator

Fluoroscopic guidance is recommended to facilitate
passage into the right ventricle; however, if this is not available, the distance from the introducer to the apex can be estimated and the lead gently advanced blindly.

The electrode is connected to the external pacing generator, the heart rate is programmed at 80 to 100 pulses/min, and the highest output current is selected

As the lead progresses closer to the cardiac chamber, pacing spikes can be seen on the surface ECG until wide QRS complexes appear when the catheter reaches the right ventricle

if pacing is lost, the lead should be slightly adjusted until capture is regained. Because of this, the lead can be held in place with tape or sutured to the patient but should remain accessible in case adjustment is needed.

Question 18

paces in what mode

This mode requires the selection of the appropriate

sensitivity value needs to be

Answer 18

VVI mode (ventricle paced, ventricle sensed, inhibition of pacing when spontaneous ventricular activation sensed)

current delivered to the endocardium
sensitivity - minimum voltage an electrical potential that the pacemaker will detect

low enough to recognize spontaneous QRS complexes but high enough to prevent detection of other electrical potentials, such as T waves

Question 19

Sensitivity between ___ & ____. What mV

Answer 19

less QRS above T

A sensitivity of 1.5 mV is usually adequate. If T waves are detected by the pacemaker and inhibit pacing, sensitivity is decreased—that is, the number is increased (e.g., from 1.5 to 3 mV)

The paced QRS complexes are wide and sometimes preceded by a pacing spike. The output can usually be selected between 0.1 and 20 mA. A starting current of 2 mA is usually sufficient