ECG basics

Question 1

heart rate calculations

• standard paper speed
• time and length of dark/light lines
• formula

Answer 1

SPS: 25 mm/sec

dark: every 0.2 sec, so 5 “big boxes” per second
light: every 0.04 sec, so 1500 “small boxes” per minute

HR = # beats in 6 seconds x 10 = 1500/# light lines between beats

Question 2

AV and IV conduction

Answer 2

AV = PR interval, less than or equal to 0.2 seconds
IV = QRS interval, less than or equal to 0.1 seconds

Question 3

QTc interval

Answer 3

less than or equal to 0.45 seconds

• from onset of QRS to end of T (depol and repol)
• QT interval varies with HR
• QTc = QT/square root of R-R interval

Question 4

right bundle branch block appearance

Answer 4

prolonged QRS

• late upward deflections in right sided leads (V1, aVR)
• late downward deflections in left sided leads (1, V6)

Question 5

left bundle branch block appearance

Answer 5

prolonged QRS

• late upward deflection in left sided leads (1, aVL, V6)
• late downward deflections in right sided leads (V1)

Question 6

AV conduction levels of heart block

Answer 6

1st degree: prolongation of PR interval only
2nd degree: some but not all beats are conducted
-Mobitz type 1: gradually increasing PR interval until a P wave is not conducted
–following P wave is conducted with shorter PR interval
–not serious, more common
-Mobitz type 2: sudden non-conducted P waves with no change in PR intervals
–more serious, but uncommon; may go to 3rd degree
3rd degree: no P waves are conducted, need pacemaker

Question 7

complications of 3rd degree heart block

Answer 7

• escape rhythm

- junctional bradycardia with BBB or ventricular bradycardia (idioventricular rhythm)

Question 8

ventricular tachycardia

Answer 8

HR > 100/min originates from one of the ventricles, resulting in a wide QRS complex
-potentially life threatening b/c can degenerate into ventricular fibrillation resulting in sudden death

Question 9

narrow VS wide QRS complexes in tachycardias

Answer 9

narrow: QRS < 100 ms are supraventricular origin, with intact IV conduction
wide: QRS > 120 ms are supraventricular rhythm with aberrant IV conduction (RBBB, LBBB), or ventricular tachycardia