Rhythm Disturbances

Escape beats might be widened and seen in (1) __________. Do not confuse them with (2) ____________.

(1) 3rd degree AV block (2) VPCs

What is sick sinus syndrome?

(1) KEY FINDING ON AN ECG is *sinus arrest [absence of electrical activity]* that can last several seconds and lead to syncope. (2) concurrent bradycardia-tachycardia syndrome

Atrial pre-mature complexes look like (1) .......But, they are occuring......(2)

(1) sinus QRS complexes (2) earlier than they should be (short RR interval) ( http://www.unm.edu/~lkravitz/EKG/prematurebeats.html )

Why are supraventricular tachycardias considered less clinically important than ventricular tachycardias in the dog? (A) Supraventricular tachycardias can occur incidentally and will usually convert back to normal sinus rhythm by themselves. (B) Ventricular tachycardia is caused by severe cardiomyopathies and is indicative of a serious underlying disease. (C) Supraventricular tachycardias may progress to atrial fibrillation and cause progressive left ventricular dysfunction, whereas ventricular tachycardias may lead to ventricular fibrillation and death (D) Supraventricular tachycardia is actually just as clinically important as ventricular tachycardia because they can both lead to cardiac arrest and death. (E) Supraventricular tachycardias are easily treated with a beta blocker or calcium channel blocker whereas the treatment for ventricular tachycardia is less efficacious.

(C) Supraventricular tachycardias may progress to atrial fibrillation and cause progressive left ventricular dysfunction, whereas ventricular tachycardias may lead to ventricular fibrillation and death

What will you see on an ECG in a dog with a pericardial effusion?

electrical alternans - R waves varies on a beat to beat basis

What are the features of hyperkalemia on an ECG?

1. From reduction of P wave amplitude OR absence of P waves altogether. 2. Increase of QRS duration (widening of the QRS) 3. Slowing of heart rate. 4. T waves become tall and spiked.

Bradycardia in a cat is ________

<100bpm

In a dog over 20kg, bradycardia is defined as

<60bpm

In a dog 20kg or less, bradycardia is defined as

<70bpm

Name two drugs that are used to slow heart rate and their mechanisms of action

Beta- blockers e.g. atenolol Calcium channel inhibitors e.g. diltiazem

AF in a horse might only affect them ____________ (at rest/during excercise). Explain

During excercise- When attempting to exercise, the atria are unable to contribute effectively, since there is poor filling of the chambers as a result of being in atrial fibrillation. However, at rest, atrial fibrillation may not cause a significant deficit in cardiac output and the horse may appear normal

Explain Mobitz I (Wenkebach)

In 2nd degree AV block successively longer PR intervals until one QRS fails ( http://www.unm.edu/~lkravitz/EKG/avblocks.html )

A tall R wave might suggest...

Left ventricular enlargement

Explain Mobitz II

PR intervals *DO NOT* lengthen will again see drops in QRS

What is the most common pathologic arrhythmia in the horse?

atrial fibrillation

A deep S wave might suggest....

Right ventricular enlargement

Describe what sick sinus syndrome is

SNS is a disturbance of the normal rhythm of the heart in adult/older dogs. Normally, a dog's heart will beat at a rate as low as 40 beats/minute during sleep and as high as 280 beats/minute during intense exercise. In sick sinus syndrome, the heart's natural ability to beat is compromised. Some dogs suddenly have a heart rate as slow as 10 beats/minute, even during physical exercise; this causes a drastic drop in circulation, and then they recover for hours or days before having another sudden drop in heart rate. Other dogs have the opposite: a heart rate that suddenly is very fast, causing a pounding heartbeat and also compromising the circulation. Overall, then, sick sinus syndrome is a disorder that causes an erratic change in the heartbeat, and that begins mildly and then develops over time into a potentially life-threatening problem. The hallmark symptom of sick sinus syndrome is sudden loss of consciousness (fainting), also called syncope.

What is the most common cause of cardiac arrest in dogs? Ventricular tachyarrhythmias Oleander Myocardial infarction Systemic hypoxemia

Systemic hypoxemia (usually due to neurologic, pulmonary, or myocardial hypoxia)

"Heart block" means

a group of disorders characterized by variable conduction from the atria to the ventricles

1st degree heart block is....

all electrical signals from the atria reach the ventricles, but the signal is slowed down slightly, i.e. there is a delay between P and QRS

What is ventricular bigeminy?

alteration between sinus beat and VPC (VPC every 2nd beat) e.g. sinus beat-VPC-sinus beat-VPC-sinus beat-VPC

Why are second degree AV blocks common in the horse?

because they have such high vagal tone. If you gave them a vagolytic drug such as atropine, these would stop

What causes VPCs (ventricular premature contractions)

heart disease GDV splenic disease hypokalemia

How can you differentiate sick sinus syndrome from 3rd degree block?

in sick sinus syndrome, there are no escape beats versus 3rd degree block will have an escape beat provided by somewhere else in the ventricle

Sick sinus syndrme will effect the following how? -Rhythm -HR -P wave -QRS

irregular rhythm HR will be slow P waves will be present QRS complexes have associated P-waves

What are the ECG findings of atrial fibrillation?

irregularity with absent p-waves *is classic* +/- f-waves (not always present) rapid rhythm in the dog

A widened p-wave might suggest....

left atrial enlargement hint- as the p widens, look like an "m" and "m" is for mitral

What breeds are predisposed to sick sinus syndrome?

miniature Schnauzers, cocker spaniels, West Highland white terriers, and dachshunds

The main ECG feature(s) of 3rd degree block is/are...

no association between P and QRS, depolarizations are escape beats

3rd degree heart block is...

none of the electrical impulses from the atria reach the ventricles. When this happens, the bundle of His or other tissues of the ventricles function as a substitute pacemaker for the ventricles, producing escape beats *atria and ventricles are deporlarising independently*

2nd degree heart block is...

not all electrical signals reach the ventricles. Some beats are "dropped," resulting in a slower and sometimes irregular rhythm.

The main ECG feature(s) of 1st degree block is/are....

prolonged PR interval

AF in a horse is treated with __________. What kind of drug is this? What is its mechanism of action?

quinidine - class Ia anti-arrhythmic - membrane stabilizers - inhibits moderate sodium channels - inhibits rate of spontaneous depolarization

Hyperkalemia will effect the following how? -Rhythm -HR -P wave -QRS

rhythm will be regular HR will be slow absent or decreased amplitude P-wave increased QRS duration

If there is a P for every QRS and a QRS for every P wave, the rhythm is _________

sinus

The main ECG feature(s) of 2nd degree block is/are...

some P waves without QRS

When you ausculate a-fib what does it sound like?

tennis shoes in the dryer (Very irregularly irregular)

2nd degree block, Type I is common in __________. It is a mechanism to __________.

the horse regulate blood pressure

What is ventricular trigeminy?

trigeminy is a *VPC every third beat*