Cardiology - ECG

Question 1

Discuss how to calculate heart rate on ECG

Answer 1

• 300 divided by number of large squares between RR

- Count off by 300, 150, 100, 75, 60, 50, 43, 37

Question 2

Discuss how to calculate heart rhythm

Answer 2

• every P wave followed by QRS
• every QRS wave preceded by P wave
• P wave axis is normal at 0-90 degrees

Question 3

Discuss how to calculate QRS axis

Answer 3

Inspect leads I and II
- QRS upward in both I and II then axis is normal (-30 to 90)
- if not then go to step 2
Inspect QRS in leads in I and aVF
- if positive in lead I and negative in aVF then left axis deviation (-30 to -90)
- If negative in lead I and positive in aVF then right axis deviation (90-180)
- if negative in both lead I and aVF then extreme right axis deviation (-90 to -180)

Question 4

Discuss findings in Q wave

Answer 4

Pathologic if width >1mm and depth >1/4 R wave and is due to previous myocardial ischemia
Inferior (RCA)
- Leads II, III and aVF
Anteroseptal (LAD)
- lead V1/V2
Anteroapical (LAD distal)
- lead V3/V4
Anterolateral (CFX)
- lead V5/V6, I and aVF
Posterior (RCA)
- V1/V2 tall R wave instead of Q

Question 5

Discuss normal findings in QRS complex

Answer 5

Narrow QRS Complex (normal) Requires

• electrical implese triggering depolarization at AV node
• functional His-Purkinje system to conduct electrical impulse at equal and rapid pace
• Cardiomyocyte able to transmit electrical impulse

Question 6

Discuss wide QRS complex causes (>120ms or >3 squares)

Answer 6

Premature Ventricular Complex
- wide QRS complex appear after certain number of normal beats
- no P wave before PVC
- only 1
Right Bundle Branch Block
- wide QRS with normal sinus rhythm
- RSR in V1, prominent S in V6 (bunny ears)
- prominent R wave in V1
- inverted T wave in V1/V2/V3/V4
Left Bundle Branch Block
- wide QRS with normal sinus rhythm
- broad notched R in V6 (W)
- Absent R and prominent S in V1
Pacemaker
Accessory Pathway

Question 7

Discuss right and left ventricular hypertrophy

Answer 7

Right Ventricular Hypertrophy
- R wave > S wave in V1/V2
- Right axis deviation
Left Ventricular Hypertrophy
- Sokolow-Lyon: R in V5 or V6 + S in V1 >35mm
- higher R wave in leads 1, aVL, V5, V6

Question 8

Discuss ST segment pathology

Answer 8

• elevation of 2 small squares right of J point (QRS) relative to baseline TP segment
• Have T wave inversion in V1-V6 for ischemia
  Reciprocal Leads
• Lateral leads to inferior leads
• Anterior leads to posterior leads

Question 9

Discuss QT interval

Answer 9

• calculated by QT duration in milliseconds / square root of RR
• normal 350-450

Question 10

Discuss the JVP Waveform and Pathology

Answer 10

Waveform:

• a is atrial contraction
• x is atrial relaxation
• c is ventricular contraction
• v is atrial venous filling
• y is ventricular filling

Pathology

• absent a wave in Afib
• Tamponade have x descent only and absent y
• Constrictive pericarditis have prominent y descent and Kussmaul sign (increase in JVP with inspiration)

Question 11

Discuss dominant circulation for the hear

Answer 11

• Posterior descending/interventitricular artery +
• branch of RCA in right dominant (80%)
• branch of LCx in left dominant (15%)
• both (5%)

Question 12

Discuss the size of the boxes

Answer 12

Horizontal
- 1mm =40ms
- 5mm = 200ms
Vertical
- 1mm = 0.1mV
- 10mm = 1mV

Question 13

Discuss trifasicular block

Answer 13

• 1st degree AV block +
• LAHF +
• RBBB