| Date | November 2016 | Marks available | 2 | Reference code | 16N.3.HL.TZ0.22 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 22 | Adapted from | N/A |
Question
The electrocardiogram (ECG) of a normal patient after exercise is shown.
Using the R–R interval in this ECG, calculate the heart beats per minute (bpm) of this patient. Show your working.
Describe the electrical activity that occurs in the heart during the P wave.
Explain why the QRS wave has a larger amplitude than a P wave.
Markscheme
a. determining time of 1 beat = 0.46 «seconds»
b. correct calculation of heart rate/beats per minute = 130 «bpm»
Other possible calculations
eg:
23 «squares» × 0.02 «sec» = 0.46
OR
2.3 × 0.2 «sec» = 0.46
OR
atrial depolarization/electrical impulse travels from the sinoatrial/SA node to the atrioventricular/AV node
Accept atrial systole.
a. atrium has a small contraction requiring low electrical charge/OWTTE
b. the QRS complex shows the depolarization of the «right and left» ventricles
Accept ventricular systole.
c. the ventricles have a large muscle mass compared to the atria, so the QRS complex has a larger amplitude than the P wave/OWTTE
OR
ventricle contraction needs more electricity than atrial contraction/OWTTE
Accept answers implying large muscle mass eg, stronger contraction, more pressure, etc.
