Cardio.Chap 46 Bradyarrhy Flashcards
Summary: Sinus bradycardia is usually secondary: Bradyarrhythmias are more common in: Most common requiring tx.: Atril standstilllook for: Medical management of bradyarrhythmias is:
systemic disease causing high vagal tone dogs than cats third-degree AV and sick sinus syndrome hyperkalemia rarely successful
Bradyarrhythmias are defined as
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
pauses may extend beyond ____ lead to syncopy
6-8s
Conduction disturbances include:
BBB, first-, second-, and third-degree atrioventricular
marked vagotonia … what happens to P-waves
wandering pacemaker, which corresponds to a variation in the amplitude of the P wave in relation to the respiratory cycle
Sinus Node Dysfunction
Sinus arrest:
sinus block:
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
Sick sinus syndrome
opioids and SSS
characterized by
breeds
-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
AV 1
causes
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
AV 2 - high grade
second-degree AV block is said to be high grade when more atrial impulses fail to be conducted to the ventricles than are conducted
Wenckebach’s phenomenon
causes:
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
Mobitz type II
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.
ddx Mobitz I vs II
atropine 0.04 mg/kg IV
type I usually improves after atropine
type II is unchanged or worsens.
AV III
Causes
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
Atrial standstill
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
Tx mx:
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.
Tx if mx. fails:
Transcutaneous pacing
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
Temporary transvenous pacemakers
leads:
Vein:
Describe technique:
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.
paces in what mode
This mode requires the selection of the appropriate
sensitivity value needs to be
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
Sensitivity between ___ & ____. What mV
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
