Heart placement

[caters]

My Kepler Bb humanoids have a double circulatory system in 2 ways.

1) Pulmonary circulation + systemic circulation(sometimes coronary is considered separate from systemic though)

and

2) 2 circulatory systems in the body. 1 heart, the right heart is normal(aorta to the left). The other heart, the left heart is inverted(aorta to the right)

And well there is a reason they have 2 circulatory systems, each with a single heart. This increases oxygen transport to all organs. In fact there are even primary and secondary coronary arteries.

Yes you heard that right, 2 sets of coronary arteries for each heart. The primary coronary arteries come from the aorta that the heart in question is connected to(so right heart, right aorta, left heart, left aorta)

The secondary coronary arteries come from a branch further down on the opposite aorta(so right heart, left aorta, left heart, right aorta)

I have heard from someone who answered my merged EKG question on Stack Exchange, that having the 2 hearts side by side makes them more vulnerable to chest shots(in other words while a shot right at the heart is less likely than before, a shot at 1 or both aortae(plural of aorta) causing severe arterial bleeding is much more likely than a lung shot causing a pneumothorax.

And defibrillation would be a problem with 2 hearts close together. They would likely have to do open heart surgery and even then there is a chance that the heart that is in V fib would not be the only one affected by the shock. There is a chance that the other heart that is in Sinus Tach to compensate for the V fib is also going to be affected by the high wattage(or in other words high electrical energy).

However, I want to keep my humanoids, humanoids, and I think that if I make the chest wider without proportionally widening every other part of the body that it will just look weird, too weird to be considered humanoid. So this leaves me with 2 options:

1) Proportionally widen every part of the body(not a good idea in my opinion because while reducing turbulence even more than having the hearts 5 inches apart to make room for the 2 aortae, increases oxygen demand to a higher norm and in that case, Sinus Bradycardia could mean heart failure(yes I know that is extreme but it could happen))

or

2) Deal with the merged EKG that is inevitably going to result and have heart surgery as a norm(No increased baseline oxygen demand but leads to close calls on EKG)

And here are a couple of those close calls I am referring to:

This is Sinus Tachycardia. HR is about 120 bpm. A rhythm strip looking like this would most likely be 2 things:

1) Synchronized Sinus Tachycardia(so both hearts have the same heart rate and same timing of contraction etc.)

2) Compensatory Sinus Tachycardia

Compensatory Sinus Tachycardia would be when the cardiac output of 1 of the 2 hearts is almost or exactly 0 due to V tach, V fib, or Asystole. But if this is the case and the rhythm strip looks like just plain Sinus Tachycardia, the heart that is problematic is in Asystole. V tach in 1 heart would lead to what looks like well, V tach. And if it is polymorphic already, then that Sinus Tachycardia just adds to the polymorphicity(if that even is a word but you know, more variety in the QRS because of fusion beats). If it is monomorphic though, it makes it polymorphic on the EKG again because of fusion beats(Sinus beats overlapping with ventricular beats). V fib in 1 heart would mean all the waveforms are fibrillatory. What I mean is that you would have a P wave, QRS complex, and T wave that all look like a sinus beat + fibrillation. But yeah this is 1 close call and in fact any rhythm that is definitely in at least 1 heart is a close call between synchronized and rhythm + asystole.

What looks like Atrial bigeminy or atrial trigeminy or atrial quadrigeminy could very well be Sinus Bradycardia in 1 heart and a Sinoatrial block in the other heart.

These are just 2 close calls.

But anyway, I want to keep this 2 separate circulatory systems thing but if I can, also want to avoid a merged EKG. I mean yes I could put leads directly on the 2 hearts but that would give a baseline that is wavy. Then of course I could have 2 sets of precordial leads and 1 set of limb leads so that I could try to detect right heart activity separate from left heart activity. But that could lead to for example RV1(Right sided V1) showing left heart activity when it shouldn't because of the placement of the leads. So an 18 lead EKG while ideal in terms of determining rhythm, is far from ideal in terms of determining whether there is pericarditis or myocarditis or MI or some other condition besides arrhythmia in either the right heart, the left heart, or rarely, both.

So how could I get the best of both worlds with 2 hearts and EKGs(Rhythm easily determined to be from right heart or left heart and other condition also easily determined to be from right heart or left heart)?

 

[Foxbat]

I'm not trying to be disrespectful but why do you need to go into so much detail? Are you writing a story or preparing to give a lecture on a double heart system?

 

[Mr Orange]

so, if i was reading your story, these are the bits that would interest me:

My Kepler Bb humanoids have a double circulatory system in 2 ways.

And well there is a reason they have 2 circulatory systems, each with a single heart. This increases oxygen transport to all organs.

other than maybe a passing mention to an unusually wide chest to accommodate this, i wouldn't want or need to know any more, and i certainly wouldn't need to know more about their biology than i do about human biology.

unless of course someone is going to get a chest shot which is a big part of the plot, in which this may be useful:

In fact there are even primary and secondary coronary arteries.

I have heard from someone who answered my merged EKG question on Stack Exchange, that having the 2 hearts side by side makes them more vulnerable to chest shots(in other words while a shot right at the heart is less likely than before, a shot at 1 or both aortae(plural of aorta) causing severe arterial bleeding is much more likely than a lung shot causing a pneumothorax.

it's science fiction after all - give them two hearts, mention a few of the downsides/effects on their physiology and leave it at that.

i know that doesn't answer the question in your post, but i'll leave that to a heart surgeon

 

[Coast]

And defibrillation would be a problem with 2 hearts close together. They would likely have to do open heart surgery and even then there is a chance that the heart that is in V fib would not be the only one affected by the shock.

The defibrillator works by shocking the V fib heart into spasm, to knock it out of the fibrillation and allow it to restart itself. As such, if you had one heart in V fib, shocking them both wouldn't really be a problem. It would just stop both and they'd restart naturally (hopefully).

But a defibrillator won't work if it detects a normal heart rate, or any type of irregular beat that it can't fix. So a human defibrillator won't work on aliens with one heart working and one in v fib, not because the shock wouldn't be effective but because it would see the other heart beat and not discharge. Is this the problem you are trying to solve? After you mention 'merged EKG's' you completely lost me...

 

[Pentagon]

So to me, you CAN have a setting which puts great effort into being extra-ordinarily descriptive, which can be fun to read, but the setting has to be entirely consistent. If I'm the kind of guy who wants to read extremely detailed settings, I would expect there to be equal 'effort' in say the engineering behind space travel, and whatever else is in your story.

If the writers interest is in biology and they want to go to great lengths, then go for it, but ensure the piece is consistent in its detail otherwise it will be a bit mad, reading a normalish story, to find 3 pages on heart surgery...

 

[hitmouse]

The defibrillator works by shocking the V fib heart into spasm, to knock it out of the fibrillation and allow it to restart itself. As such, if you had one heart in V fib, shocking them both wouldn't really be a problem. It would just stop both and they'd restart naturally (hopefully).

But a defibrillator won't work if it detects a normal heart rate, or any type of irregular beat that it can't fix. So a human defibrillator won't work on aliens with one heart working and one in v fib, not because the shock wouldn't be effective but because it would see the other heart beat and not discharge. Is this the problem you are trying to solve? After you mention 'merged EKG's' you completely lost me...

Re the defib not working if it detects a normal heart rate, it depends on the type of defib. Until about 15 years ago they were mostly manual triggers and could be fired at any point unless deliberately set to synchronised shock for specific therapeutic reasons. The more sophisticated defibs used today (not the automatic ones for use by lay people) can still do this.

I have spent a lot of time dealing with the technical aspects of cardiac physiology and I have to say with respect that your descriptions are pretty baffling. If you are describing a system with such obvious weaknesses then it would be interesting from a biological perspective to write about the evolutionary advantages that allow this particular arrangement to develop in the first place.

 

[ralphkern]

Okay, for starters, unless you're doing a medical xenobiology type story where this is relevant, then this seems a hell of a lot of depth for what might boil down to a few lines. As a hard SF fan, if you simply said they had two hearts... I'd probably go with that and not worry overly.

That being said, I understand the value of research and personally have spent hours looking up things which sum up to a sentence.

Here are some thoughts:

1. You are taking the hearts in isolation. You appear to be describing the effect of having two hearts on a human system. If it were alien, then all the ancillery organs would complement this arrangement as well. Who knows, maybe they have glands or organs which regulate the two seperate heart functions. (handwavium)

2. You appear concerned about the increased width of the chest from a side by side arrangement. What about an over and under configuration? One higher in the chest than ours, and one lower. Still seems overly complicated to me.

3. Still, if oxgenation is the issue... why wouldn't they just have a more efficient single system? Evolution tends to favour KISS (Keep It Simple Stupid) as much as anyone else.

So to me, you CAN have a setting which puts great effort into being extra-ordinarily descriptive, which can be fun to read, but the setting has to be entirely consistent. If I'm the kind of guy who wants to read extremely detailed settings, I would expect there to be equal 'effort' in say the engineering behind space travel, and whatever else is in your story.

If the writers interest is in biology and they want to go to great lengths, then go for it, but ensure the piece is consistent in its detail otherwise it will be a bit mad, reading a normalish story, to find 3 pages on heart surgery...

I get your point (and the engineering is what floats my boat), but if the POV character is a heart surgeon (or xenobiologist or whatever) then I'd expect them to be interested in the above, and perhaps not in the engineering of the spacecraft or whatever. Cawdron did that well in Xenophobia. His MC is a doctor and while alien spacecraft are interesting to her, but she doesn't care about them nearly as much as the aliens themselves. That being said, he did have a consistent level of research - it's just that the alien spacecraft workings were behind the scenes a bit more so to speak.

 

[tinkerdan]

Okay; I'm not saying all those words confused me: oh yes I am.

My premed student is inaccessible just now so I have to wing this a bit.

What intrigues me is why.

The Centauri on Babylon 5 had two hearts. (I can't remember why.) So maybe why isn't that important to the reader.

But for you, the writer, why did they develop a second heart. More so though is the question of how do they operate in the sense that you say two circulatory systems. Do they overlap or is there a left system and a right system.[You may have said that up there, but once again; no med student this week.] I'm not sure about all that medical science about monitoring them separate because I'm not sure how the two operate. It sounds like they overlap; so then the question is, are they redundant. If they are redundant than maybe a wound in one would be less fatal at first as the other just works harder. But there in lie all the good stuff, because really what you are fretting over sound like opportunities to demonstrate the weaknesses of this evolution and the conflict in the story. Still you might need to know the strengths that go with it.

Seems like you are going the overlap route and when I think about that I think of the lungs. We have two and if one goes bad we can still live, just not as well. So maybe with two hearts, when one goes bad the quality of life changes, but you don't have to die. But while you are at it maybe two hearts require four lungs, which gets you back to a larger chest cavity. Or maybe the hearts are smaller and they don't really process more oxygen into the system. Or maybe there are four lungs and the hearts are between sets of lungs and are separated by a distance of two lungs. Maybe the lungs are smaller or maybe they are longer to minimize the chest cavity width. In fact maybe the aliens are taller with long stretchy lungs and long hearts.

That's their name the Long Hearts.

 

[TheDustyZebra]

The Doctor has two hearts, and nobody cares why or what difference it makes, as far as I know. It only becomes important when one of them stops.

 

[Coast]

The more sophisticated defibs used today (not the automatic ones for use by lay people) can still do this.

Yes, sorry. I was thinking of the automatic ones that you would come across at workplaces or public spaces, not the types you'd find in a medical setting.

 

[Aquilonian]

1) There is no need for anything like this amount of detail, unless maybe the characters in your book are all cardio physicians. But even if they were, they wouldn't ever spell all this out to each other, cos they already know it, it would only come up if one of them was giving a lecture to students.
2) Two hearts is perfectly believable, other vital organs are often paired ie kidneys, lungs, eyes, ears.
3) But every evolutionary development must be worth the "price" ie must confer sufficient survival advantage. Two hearts could be useful if it means you survive an injury to one heart, like a spear or bullet, but for that to work they'd need to be far enough apart with membranes and even bones between them. Maybe an abdominal heart below the diaphragm? Degenerative heart disease would likely affect both hearts so having two would not be an advantage in evolutionary terms.
4) Making corrective heart surgery the norm is not believable because the species could never have evolved and survived long enough to develop surgery, and its hard to see how they could have grown an extra heart after they'd evolved that far if it was deleterious to their health.
5) As to being too wide to be humanoid, Abby and Britanny Hensel have two hearts and they're not only humanoid but human! Their body is wider than usual, but not massively.

 

[RX-79G]

The characters have two hearts, and this is very important because of some part of the plot, right?

 

[Mirannan]

I'd like to point out something not so far mentioned.

One thing about the human circulatory system that causes problems is that there is no active return pumping of de-oxygenated blood to the heart; it relies on compression of the leg veins caused by the contraction of leg muscles. (Hence such problems as DVT, varicose veins...)

It's at least conceivable that a secondary heart, perhaps located in the lower abdomen, with the function of actively pumping "used" blood back to the primary heart would be beneficial; perhaps giving greater endurance, for example. This would obviously require some of the veins to have thicker walls, among other things. I believe that Niven's Pak protectors have something like this in place. It would only have to have two chambers, at most - maybe only one.

Incidentally, this would be especially important in high gravity. I can well imagine a venous system heart being part of the suite of modifications for genetically engineered human variants designed for high-G worlds - or perhaps for geneered space fighter pilots.

 

[hitmouse]

I'd like to point out something not so far mentioned.

One thing about the human circulatory system that causes problems is that there is no active return pumping of de-oxygenated blood to the heart; it relies on compression of the leg veins caused by the contraction of leg muscles. (Hence such problems as DVT, varicose veins...)

I am afraid that that is incorrect. The venous muscle pump in the legs is helpful during exercise, but it does not substitute for the "active return" pumping actions of the right side of the heart. Think about it: if all we had to rely on was the actions of the leg muscles then we would run into difficulty as soon as we sat down or went to sleep. The right side of the heart is critical in this respect. In conditions which lead to right heart failure, such as certain types of heart attack, fluid oedema accumulates in the legs and dependent areas, the liver becomes congested with blood, and a number of other difficulties.
DVT and varicose veins are separate conditions.

 

[RX-79G]

I am afraid that that is incorrect. The venous muscle pump in the legs is helpful during exercise, but it does not substitute for the "active return" pumping actions of the right side of the heart. Think about it: if all we had to rely on was the actions of the leg muscles then we would run into difficulty as soon as we sat down or went to sleep. The right side of the heart is critical in this respect. In conditions which lead to right heart failure, such as certain types of heart attack, fluid oedema accumulates in the legs and dependent areas, the liver becomes congested with blood, and a number of other difficulties.
DVT and varicose veins are separate conditions.

I think this is somewhat chicken and the egg. While the right side might serve as a negative pressure pump, the effectiveness of any draw pump that is working on a deformable hydraulic system is going to be pretty poor. Without the positive upstream pressure and check valves, the right side of the heart would just suck the veins flat. The system works as a whole because everything is in balance.

And edema does occur when healthy people sit upright without moving for too long, as opposed to lying flat which lowers return pressures.

 

[Mirannan]

I think this is somewhat chicken and the egg. While the right side might serve as a negative pressure pump, the effectiveness of any draw pump that is working on a deformable hydraulic system is going to be pretty poor. Without the positive upstream pressure and check valves, the right side of the heart would just suck the veins flat. The system works as a whole because everything is in balance.

And edema does occur when healthy people sit upright without moving for too long, as opposed to lying flat which lowers return pressures.

Point taken. It might be better to say that the negative pressure induced by the contraction of the right side of the heart, and the pumping action of leg muscles. work together. This must be so, else one wouldn't have issues cropping up such as oedema caused by inactivity and also the well-known phenomenon of soldiers fainting when they have been standing at attention for a long time. The system has to overcome a head of (at the extreme, venous blood return from the feet) around 1.5m on average. If there was a return pump somewhere like the lower abdomen, this would be considerably less.