ECG Interpretation

Question 1

Frontal plane

Answer 1

an imaginary cut through the heart from top to bottom and side to side providing information about the inferior and lateral wall of the heart (Limb Leads).

Question 2

Horizontal plane

Answer 2

a cross-sectional view front to back and side to side providing information about the anterior, septal, lateral and posterior wall of the heart (Chest/Precordial Leads).

Question 3

ECG Paper (speed)

Answer 3

Each small box represents 1mm/0.04 seconds.
Each large box represents 5mm/0.20 seconds.
Normal speed at which the strip runs across the screen (and prints) is 25 mm/sec.
Doubling the speed is useful with very fast rhythms.
Each ECG strip is normally 6 seconds.
5 large boxes is 1 second.

Question 4

ECG Paper (voltage)

Answer 4

One small box is 0.1mV/1mm
Five small boxes is 0.5mV/5mm
Standard is what they are usually recorded at, two large boxes.
Half-standard is sometimes what they are recorded at due to adipose tissue/heart failure, one and a half large boxes.

Question 5

Isoelectric line

Answer 5

areas of the ecg where there is no depolarization or repolarization occuring.

Question 6

P wave and PR interval

Answer 6

Question 7

QRS Complex

Answer 7

Question 8

ST Segment

Answer 8

Question 9

T wave and QT interval

Answer 9

Question 10

QT Interval and QTc

Answer 10

Question 11

U wave

Answer 11

Delayed repolarization of the Purkinje fibers.
Usually goes in same direction as T wave.
Rarely seen as a result of its small size.
More commonly seen in bradycardic rhythms.
Has many causes, including possible hypokalemia.

Question 12

1500 method

Answer 12

Count the number of small boxes between two R waves and divide 1500 by that number. This is only accurate if the rhythm is REGULAR.

Question 13

300 method

Answer 13

Count the number of large boxes between two R waves and divide 300 by that number. Stop counting PRIOR to the next R wave.

Only gives an estimate!

Question 14

QT interval and QTc

Answer 14

• Measured from the beginning of the QRS complex to the end of the T wave.
• Measures the refractory period.
• Normal (less than or equal to) 0.44 seconds or half of the RR interval.
• The QT interval can be lengthened by cardiac ischemia, electroly disturbance and over 300 different medications.
• The longer the QT interval, the more likely a trigger will occur casuing Torsades de Pointes. Prolongation may suddenly cause a chaotic and lethal rhythm.

Question 15

ST segment

Answer 15

Between the end of ventricular depolarization and the beginning of repolarization.
The ST segment starts at the J-point and ends at the start of the T-wave.
Normal: up to 1 or 2 mm elevation (depending on the lead); up to 0.5mm depressed.