This is the most difficult a level bio question I’ve seen

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I can’t even start.
Upon looking at the MS
All I could comprehend were marking points 1,2,4 and 5.
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Last edited by CurrentlyAtLevel; 3 years ago
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(I have an unfair advantage of having seen cardiac patients and therefore a large number of ECGs - I shall try to put myself in the shoes of an A level student)

3. If you look at the intervals (on x axis = horizontally) between the beats , this interval is steady on the ECG on left [normal], but is shorter between the 1st normal beat and the ectopic beat on ECG on right [abnormal], yeah? So the ectopic beat is premature i.e. it has come too early.
6. ECG on right [abnormal]: For the interval between the 2nd [= ectopic] beat and the 3rd beat [normal one] the gap is much longer, so this tells you that "a beat has been missed" [to put it simply], with me?
7. (v unfair Q for A level): the pulmonary artery pressure trace on right (abnormal) shows no peak at the time of the ectopic beat [looking directly vertically below the abnormal ECG above it], so this tells you that there was effectively no blood pumped out by the heart in timing with the ectopic beat [however, it is actually not ideal to measure pulmonary artery pressure here but aortic pressure, but I suppose at A level, these items cannot be fully correct [the examiners are extremely unlikely to be doctors]].
8. (look up refractory period in your books).
9. (difficult to predict this wording i.e. difficult to read examiner's mind here)
10. (as in 8).

EXTRA INFO: Yes, this is a very difficult Q for A level.
1. An ectopic beat has a different waveform from normal beats (you can see that the shape of "E" is very different from that of the other QRS complexes.
2. "E" has no P wave before it, yeah? Do you remember what generates the P wave? ……………………………………………………………………...Yes, correct: atrial depolarization - so the absence of a P wave tells you that this is a VENTRICLAR ectopic beat (although you would get a similar ECG with a junctional ectopic beat (= one originating in the junction between the atria and the ventricles)
3. (NB: ONLY for super-nerds or budding cardiologists): There are several other highly complex ways of distinguishing between ventricular and supraventricular (supra = above so above ventricles = originating in atria or junctional area) ectopic beats BUT MIGHT JUST BE USEFUL TO NOTE ONE ITEM IN THIS Q:- If you measure the time interval between the normal beat (abnormal trace [on right]) i.e. 1st beat, and the next normal beat on the same trace (right one) i.e. 3rd beat, it is twice the distance between individual beats on the normal trace (left one}. Assuming that the traces are from the same patient at different times RATHER THAN from different patients, this tells us that the last beat (3rd one - one after "E") in the abnormal trace (right one) occurs when expected - this is one clue to the ventricular origin of the ectopic beat [because the electrical activity generated cannot travel retrogradely (backwards) to the SA node and so the pause between the ectopic beat and the next normal beat is a "compensatory" one, NOT shorter [due to an early conduction from the SA node of the retrogradely transmitted impulse] OR longer.

Most students: please ignore text in italics.


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