My humanoids have 2 hearts that are about 5 inches apart in the chest(this is to make room for the 2 aortas to minimize turbulent flow). However on an EKG, the rhythm of the right heart and the rhythm of the left heart might merge and this could be problematic.

For example here is what might show up from A fib of 1 heart when the other heart is at the same heart rate but without any arrhythmia:

enter image description here

You can see that the fibrillation has merged with the normal EKG to form these fibrillatory P waves, fibrillatory QRS complexes, and fibrillatory T waves.

Now granted, this would more likely happen in someone with V fib in 1 heart but it could happen in someone with A fib in 1 heart.

And don't comment on my terrible drawing of an EKG because I know it is terrible. I know I get what look like PVCs and AV blocks and Sick Sinus Syndrome etc. But really I am just trying to get across the sequence of waveforms or that there is fibrillation.

Anyway, this merged EKG would be tough to determine, especially with A fib and V fib since with fibrillation it can be hard to know whether those bigger waveforms are just fibrillation at a higher voltage or whether they are the result of fibrillation merging with the other heart that doesn't have fibrillation(fibrillatory P waves, QRS complexes, and T waves I mentioned earlier).

Asystole of 1 heart + NSR(normal sinus rhythm) in the other heart can look just like the normal synchronized NSR so that is another close call. Though usually the heart rate will be faster if 1 of the hearts is in V fib or asystole than it would otherwise so sinus tachycardia would more likely happen to compensate for the V fib or asystole.

Defibrillation would be much more complicated and they would likely have to do open heart surgery every single time or insert an ICD.

Anyway, how can I avoid merging of the EKG while not having leads directly on the hearts(would lead to a wavy baseline that could easily be mistaken for A fib or atrial flutter) but still keep the 2 circulatory systems my humanoids have? I don't think extra leads is enough.

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    $\begingroup$ Quick sanity check: you're worried about the ability to read the diagnostic tools, right? (as opposed to worrying about the body not functioning due to the two hearts) $\endgroup$ – Cort Ammon Jan 7 '17 at 19:52
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    $\begingroup$ Idea that different humanoids, with different system, would use our method is naive. Probably they will either have both hearts in sync anyway, or will develop a method with electrodes and a way of reading resulting lines, that will let them see what they need to see. $\endgroup$ – Mołot Jan 7 '17 at 19:52
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    $\begingroup$ You might get a better answer at signal processing SE $\endgroup$ – Mrkvička Jan 7 '17 at 20:07
  • $\begingroup$ @Mrkvička No, OP won't, unless he rephrases it to a signal processing question. I think this about "creature design" and not about signal processing at all. He copy and pasted this in verbatim worldbuilding.stackexchange.com/questions/67160/… , and it doesn't make any sense on signals.stackexchange.com $\endgroup$ – Marcus Müller Jan 7 '17 at 23:08
  • $\begingroup$ @MarcusMüller I disagree. OP asks "how to keep two EKG signals separated without changing creature design?". If OP want to use modern, human, tech and want an actual answer for how to keep the signals separated, then I'd argue that signal processing will give a much more detailed and accurate answer; if OP want to use alien tech, then the answer can be anything close to hand waving. $\endgroup$ – Mrkvička Jan 8 '17 at 13:02

If the hearts were to be put close together, then their ECG traces would be separate in exactly the same way as the heart ECG of a fetus appears alongside the mother's ECG during gestation in human beings (again, two completely different circulatory systems). In that case, the fetus ECG is at a higher frequency (smaller organism) and lower amplitude than that of the mother.

It is possible to extract the fetal ECG from a single lead abdominal ECG system; however, the typical way to acquire signals in this case is to add more and more electrodes at specific locations to be able to discriminate the different electrical sources in a better way than just a three lead system.

Will there be margin for misinterpretation such as the one described in the question? Yes, but that would be very very small because superposition in a specific direction could be resolved by leads oriented in a different direction.

I am assuming here that the two hearts are supporting different circulatory systems (?) as that makes very good (survival) sense. In that case, it would not be good to put them side-by-side. First of all, a hit at the general area of the heart would take out both organs and that is not very good from a survival point of view. Secondly, you can forget about defibrillation, at least in the classical way because the electrical field would likely affect both organs. But, if you positioned the hearts well apart, that would increase the resilience of the creature and enable the use of current defibrillators developed here on earth to revive them. Except if their heart size is different in which case the defibrillator would need a setting to adjust its power.

Hope this helps.

  • $\begingroup$ I wouldn't really say that the heart of a fetus and a mother are close together. The fetus' heart is also measured in a completely different way: Cardiotocography (CTG) of the baby measures the heart rate (and the mother's contractions if done during labour), this is done with a belt placed around the mother's belly. Electrocardiography (ECG/EKG) of the baby measures the electrical activity and the pattern of the heart beats and is performed by placing electrodes into the scalp of the baby (through the cervix of the mother). This way you (almost) only pick up the baby's signal. $\endgroup$ – Mrkvička Jan 8 '17 at 14:54
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    $\begingroup$ Thank you for your comment, I do not see any major disagreement here. There are however multi-lead montages used during pregnancy to monitor fetal condition and this is what I had in mind when writing this response here. $\endgroup$ – A_A Jan 8 '17 at 19:36
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    $\begingroup$ Ah, thank you for that information, it was news for me. Where I live they use ultrasound exclusively to evaluate the heart at all points during the pregnancy, except for the delivery where they use the scalp EKG. I did, at first, consider your answer blatantly wrong, but as I stand corrected I would like to change my voting. If you do an edit to your post, then I'll be able to switch to an upvote. $\endgroup$ – Mrkvička Jan 8 '17 at 20:30
  • $\begingroup$ @Mrkvička Thank you. I appreciate blatant honesty immensely. From my point of view, I do not consider this as such a big issue to warrant an edit to the post and the link is available here in the comments. Multi-lead fetal ECG is not standard but it is a valid technique. Changing (or not) the vote is a power that is entirely left to you. All the best. $\endgroup$ – A_A Jan 8 '17 at 21:28

I think such a being with 2 hearts would have two distinct hearts, in tge same role that we have a double pump in one organ. So the ideas of A-fib and V-fib won’t make sense for these hearts, since they won’t be a pair of double pumps but two distinct simple pumps.

Each heart will have a much simpler pattern of electrical activity. Each can be picked up separately, and interpreting them will be more straightforward.

  • $\begingroup$ I do believe that a pair of double pumps is best. Single pumps are only useful if all their breathing is via their skin. And how could 1 atrium have a blood pressure of 5 mmHg and 1 ventricle have a blood pressure of 130 mmHg leading to an aortic pressure of 120 systolic? So since all their breathing is through their lungs, a pair of double pumps is best to achieve that pressure difference. So like 2 human hearts, not a right heart and left heart separated so much they are in themselves hearts(1 heart leads to pulmonary, other heart leads to systemic). $\endgroup$ – Caters Jan 13 '17 at 13:31
  • $\begingroup$ A pump for the lungs and a pump for the circulation is what I was supposing. See e.g. squid. $\endgroup$ – JDługosz Jan 13 '17 at 13:40
  • $\begingroup$ I know that was what you were supposing but that is not what I was thinking at all. I was thinking more like the pulmonary artery for each heart being at 90 degrees from where it is in us and thus 4 branches of 2 pulmonary arteries and the left heart being inverted to make room for the left aorta to be in the middle of the chest and thus 2 double pumps. This is better in terms of oxygen transport to all organs and would maintain the 2 sets of coronary arteries per heart. $\endgroup$ – Caters Jan 13 '17 at 16:41
  • $\begingroup$ Why would that evolve? Is there any precedent in the animal kingdom? $\endgroup$ – JDługosz Jan 13 '17 at 16:45
  • $\begingroup$ There are a few humans that have 2 hearts but they don't have 2 circulatory systems, just 2 hearts. And like I said in my question, high oxygen transport, faster vascularization, and more cardiac stem cells all point towards 2 side by side circulatory systems, each with 1 4 chambered heart and the lungs being more centered. I mean, how else could each heart have 2 sets of coronary arteries? $\endgroup$ – Caters Jan 13 '17 at 21:01

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