Cardiology

Question 1

What is the origin of the normal cardiac electrical impulse and describe the pathway of impulse transmission (AKA conduction) through the heart.

Answer 1

• Generated in the SA node
• Conducted rapidly through atria (atrial systole) > conducted through AV node slowly > rapidly conducted through the bundle of HIS > then right and left bundle branches comprised of Purkinje fibers > depolarize myocytes > ventricular systole > ventricular repolarization

Question 2

What limb locations and charges do the three standard leads represent?

Answer 2

• White on the front right limb
• Black on the front left limb
• Red on the left hind limb

Lead I = RF- to LF+
Lead II = RF- to LH+
Lead III = LF- to LH+

Question 3

How do you calculate heart rate based on two in-class methods?

Answer 3

• Find paper speed, count QRS complexes in 30 large boxes
• For 25 mm/sec multiply by 10
• For 50 mm/sec multiply by 20

OR

• As long as the rhythm is regular, count the number of small boxes in 1 RR interval
• For 25 mm/sec divide 1500 by # of small boxes
• For 50 mm/sec divide 3000 by # of small boxes

Question 4

What does each component of the PQRST represent? Know how to measure them on an ECG.

Answer 4

• P-wave = atrial depolarization
• QRS = ventricular depolarization
• T = ventricular reploarization
• PR interval = atrial depolarization and AV conduction
• QT interval = ventricular depolarization and repolarization
• RR interval = time between ventricular depolariazations
• ST segment = time between end of ventricular depolarizarion and the begining of repolarization
• PR segment = time between atrial depolarization and begining of ventricular depolarization

Question 5

What is the normal duration of a canine and feline QRS complex?

Answer 5

Canines: less than 60ms
Felines: less than 40ms

*narrow is normal, anything higher than that is considered wide

Question 6

What are the six steps in ECG interpretation?

Answer 6

1. General assessment
2. Calculate HR
3. Measure RR intervals (regular vs irregular)
4. Examine each PQRST
5. Identify ectopic complexes
6. Identify pauses

Question 7

What are the ECG criteria for a sinus arrhythmia?

Answer 7

Greater than 10% variation in RR intervals (regularly irregular)

• HR accelerates during inspiration
• HR decelerates during expiration
• Normal HR is often low normal

*Be able to identify a sinus arrhythmia

Question 8

Which species is a sinus arrhythmia normal and common in?

Answer 8

Respiratory sinus arrhythmia common in resting dogs, but abnormal in awake cats

*Exaggerated in some patients with certain respiratory diseases

Question 9

What are the three mechanisms of arrhythmia formation? And what are the names of the arrhythmias that belong to each mechanism?

Answer 9

1. Disturbances of impulse formation (excitability)
   - Sinus (SB, ST)
   - Supraventricular (SVPCs, SVT, A fib, A flutter)
   - Ventricular (VPCs, VT, V fib, AIVR)
2. Disorders of impulse transmission (conduction)
   - Atrioventricular block (first degree, second degree, third degree)
   - BBBs
   - Atrial standstill
3. Complex (disorders involving both impulse formation and conduction)
   - SSS
   - Electrolyte derangements

Question 10

What is the breed disposition for A-fib in canines?

Answer 10

Giant and large breed dogs

Question 11

What is the breed disposition for sick sinus syndrome in canines?

Answer 11

Miniature schnauzers
West highland white terrier
Dachshunds
Cocker spaniels

Question 12

What are the three differentials for a wide QRS complex?

Answer 12

1. VPCs
2. BBBs
3. Electrolyte derrangements

Question 13

What types of electrolyte derangements cause arrhythmias?

Answer 13

• Hypokalemia causes VPCs and APCs
• Hyperkalemia causes prolongation of normal waves and in severe cases V-fib and pulseless electrical activity
• Hypomagnesemia causes VPCs, VT, AIVR
• Hypocalcemia causes lower AP threshold and prolongs QT interval
• Hypercalcemia raiser AP threshold causing bradycardia, shortened QT interval and VPCs

Question 14

What are the ECG abnormalities that are associated with hyperkalemia and hypokalemia?

Answer 14

• Hypokalemia causes VPCs and APCs
  (prolongs repolarization)
• Hyperkalemia causes prolongation of normal waves and in severe cases V-fib and pulseless electrical activity and electromechanical dissociation
  (in mild, shortens repolarization, tented T waves)
  (more moderate, prolongs transmission velocity, wide QRS complexes)
  (severe, prolongs PR interval or absent P waves seen)

Question 15

What factors do hemodynamic effects depend on?

Answer 15

• Ventricular rate (if HR is too high ventricles don’t have time to fill so SV decreases if HR is too low ventricles are not ejecting enough blood)
• Duration of the abnormal rhythm
• Inherant myocardial and valvular function
• Temporal relationship between atria and ventricles
• Extra-cardiac influences