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:
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.