Clinical Interpretations of ECG I Flashcards Preview

CAM201 Clinical Skills > Clinical Interpretations of ECG I > Flashcards

Flashcards in Clinical Interpretations of ECG I Deck (22):
1

Electrode

An electrode is a conductor through which electric current leaves the body. 

2

Lead

A lead is the electric potential between two defined electrodes (represented by the tracing). 

3

1 small square translated to what on the Y axis?

0.1mV

4

One small square translates to what on the X axis?

0.04s

5

What is the normal paper speed?

25mm/sex

6

PR interval

Beginning of P to the beginning of QRS complex

7

QRS interval

Beginning of Q to end of S

8

QT interval

Beginning of QRS complex to end of T wave

9

What do you check on an ECG?

  1. Patients name, age and gender.
  2. Date and time of trace. 
  3. Check paper speed and calibration. 

10

Describe the things we look at when analysing an ECG

  1. Rate
  2. Rhythm
  3. Axis
  4. P wave
  5. PR interval
  6. QRS complex
  7. ST segment
  8. T wave
  9. (QT interval)
  10. (U wave)

11

How do you calaculate rate?

(i) R-R interval method

  • 300 divided by the number of large squares between two consecutive R waves. 

It can only be used if rhythm is regular. 

 

(ii) Six second method

  • The number of cardiac cycles in 6 seconds multiplied by 10 

It can be used of rhythm is regular or irregular. 

12

Rate abnormalities

Tachycardias or tachyarrhythmias

  • Faster than normal rate (>100bpm)

Bradycardias or bradyarrhythmias

  • Slower than normal rate (<60 bpm)

13

Rhythm

Regular

Sinus rhythm

  • Every P wave must be followed by a QRS complex
  • Every QRS complex must be preceded by a P wave

Other: eg. SVT, VT

Irregular

Regularly irregular

  • e.g. second degree heart block, ventricular bigeminy/trigeminy etc.

Irregularly irregular

  • e.g. AF

14

Calculating axis via the two-lead method

Examine QRS complexes wave in lead I and aVF. 

  • If both predominanly positive, axis is normal
  • If I is positive, aVF is negative, left axis deviation
  • If I is negative, aVF is positive, right axis deviation
  • If both leads predominanly negative, extreme right axis deviation. 

15

Calculating axis via the three-lead method

Examine polarity of R wave in leads I, II and III.

  • If all three are predominantly positive, axis is normal
  • If I is positive, II and III are negative, left axis deviation.
  • If I is negative, II is biphasic or positive and III is positive, right axis deviation
  • If all three leads predominanly negative, extreme right axis deviation. 

16

P wave

Duration: 0.04-0.12 sec

Heigh: 1-3mm

17

PR interval

0.12-0.20 sec

18

QRS complex

Duration: 0.05 - 0.11 sec (approximately 1-3 small squares)

Q wave normal if:

  • <25% R wave voltage

Rule of thumb:

  • <10mm in limb leads
  • <20mm in chest leads

19

ST segment

Duration not important. 

Morphology

  • ST elevation
  • ST depression

20

T wave

Voltage (height)

  • Should not exceed 50% to 1/3 preceding QRS complex

Generally same net deflection as preceding QRS complex. 

21

QT interval values

Varies between males and females. 

Needs to be corrected for heart rate. 

Normal QTc interval = 350-450ms

22

U wave

Normal in children and young adults. 

Prominent U waves:

  • Hypokalaemia
  • LVH
  • Mitral valve prolapse