Heart Failure

The heart is basically a pump that provides the force needed to circulate blood and its contents to the body. It consists of four chambers: left ventricle, left atrium, right ventricle, and right atrium. The right ventricle and atrium collect the blood from the whole body and pump it to the lungs for removal of carbon dioxide and replenishment of oxygen. On the other hand, the left ventricle and atrium are responsible for collecting the blood from the lungs and pumping it to the body through the aorta (main artery). Non-stop blood circulation requires life-long and unfailing heart muscle power. Common symptoms of heart failure include waking up at the middle of night with shortness of breath and decreased ability to walk a few steps upstairs. Heart failure could arise due to any condition that decreases efficiency of the myocardium (heart muscle – Figure 1) through myocardial infarctions (death of muscles due to lack of oxygen, also known as heart attack) or overloading, such as hypertension, that requires increased contraction force. Loss of function in the ventricles (lower chamber of the heart) may require the use of ventricular assist devices (VAD).

Ventricular assist devices

A VAD is a mechanical pump that is implanted into the chest of patients to support the heart function through bridging the blood flow from the lower chamber to the aorta (Figure 2).^2,3 A VAD is usually useful during or after cardiac surgeries until recovery of the heart or while waiting for a heart transplant. VADs could also be used long term if the patient is not eligible for a heart transplant due to other complications. A VAD has several components, including a tube carrying blood out of the heart into a pump, a pump with another tube carrying blood to the aorta, and a power supply connecting to a control unit that monitors the VAD`s functionality.

There are different designs of VADs such as HeartMate, HeartWare, DuraHeart, and so on. Some VADs pump like the heart does, using a pumping action, and others use continuous blood flow. Intriguingly, VADs with continuous flow lead to a loss of normal pulse, but this has been found to decrease complications and increase survival. Two types of VADs include left ventricular assist device (LVAD) or right VAD (RVAD). LVADs are the most commonly used ones due to higher incidence of left ventricular function loss. If both LVAD and RVADs are used together, they are called a biventricular assist device (BVAC). VADs nowadays could be used not only for people with end stage heart failure, but also earlier stages of heart failure, including children. A VAD takes ninety percent of the pumping function of the heart. When using a VAD, your heart will still beat and have a rhythm. If none of these works for a patient, this requires the use of a mechanical or artificial heart, also known as total artificial heart (TAH).

Total artificial hearts

An artificial heart is a mechanical device that substitutes for the failing heart.^4,5,6 They are commonly used during heart transplantations to bridge the blood flow temporarily or to replace the heart permanently during a shortage of transplantable hearts. Early studies with artificial heart trials go back to the 1940s. Since then, various groups worldwide have invested in development of artificial heart prototypes and performed animal and human trials. Total artificial heart prototypes include, but are not limited to, SynCardia, ABIOMed (AbioCor), and Carpentier (CARMAT).6

SynCardia is developed from the Jarvik-7. It was first implanted in 1982. Dr. Robert Jarvik originally designed the Jarvik-7 (Figure 3). Barney Clark underwent the first artificial heart implantation at the University of Utah and survived for 112 days. This was followed by other implants. The longest survival with the Jarvik-7 is 620 days. However, the device is more commonly used on patients as a bridge during heart transplants. It has two pumps that resemble the two ventricles of the heart and is pneumatically (air) powered. The pump of SynCardia is covered with polyurethane. A pneumatic driver used in the US is a non-portable console, and requires patients to stay in the hospital. However, a portable version has been developed in Europe that could be carried a backpack while a patient waits for a donor heart.

The ABIOMed (AbioCor) is a completely self-contained, total artificial heart, which avoids the need for an external console or having wires or tubes piercing the skin to power the device. It uses a wireless energy transfer system, also known as a transcutaneous energy transmission system. This decreases the risk of developing infections due to implants.

CARMAT, on the other hand, is designed by Alain F. Carpentier.⁷ It is a fully implantable artificial heart with embedded biomaterials that make the device more biocompatible. In addition, the CARMAT includes valves made from cow heart tissue and has internal pressure sensors. This allows a person to adjust the flow rate in response to increased demand, such as during exercise. This feature distinguishes the CARMAT from other artificial hearts that provides a constant flow rate.

Biological artificial hearts

Synthetic replacement of organs is one of the long-sought dreams of modern medicine. To this end, there are efforts to develop biological artificial hearts in the laboratory. One recent study took the approach of producing a decellurized (empty from cells) scaffold of a mouse heart and recellurized it with human cardiac cells, and showed that lab-grown human heart tissue can beat on its own (about 40-50 beats per minute) in as short as a few weeks (Figure 4).⁸ They took the advantage of induced pluripotent cell (iPS cells) technology to produce multi-potential cardiovascular progenitor (MCP) cells, which could give rise to all three types of cardiac cells found in the heart. This area of research is still in its infancy but in the future, at least, it may provide tools to generate patches of heart tissue to replace damaged parts of the hearts. Given the success of a mouse heart cellurized with human cardiac cells, it’s possible that scientists will also try to decellurize the heart of a monkey or another animal and then cellurize it with human cardiac cells to produce a beating human heart in the laboratory as an alternative source to a full heart transplant.

Another approach to a biological artificial heart is to genetically modify animals in a way that their hearts will be compatible with a human body. Genetic engineering is a rapidly evolving field that one day could provide such tools for scientist to grow necessary organs in monkeys, dogs, or maybe even horses. Genetic modification may overcome tissue rejection issues when they are transplanted into a human body. For instance, one study tested the possibility of a heart transplant from genetically modified pigs into monkeys and showed the applicability of heart transplants between different species.^9,10

Until the development of biological artificial hearts, ventricular assist devices and mechanical artificial hearts seem to the best options. However, artificial heart implants have had various complications, including infections, pneumonia, high fevers, and multiple organ failures with variable survival rates based on the type of device and materials used. Another issue is the necessity of artificial heart to meet requirements of the body in terms of heart flow rate. For instance, the required flow rate of someone walking or exercising is different than someone at rest. In addition, the possibility of mechanical or computerized systems to fail may be a source of distress in patients implanted with artificial hearts or assist devices. This reminds us of that as long as we take care of our heart’s health, we won’t have worry whether its battery could fail – and what a mercy that is.

It is stunning that even with so much need and effort we are still not able to develop something that completely replaces all the functions of a heart. This clearly points that the heart is a marvelous gift granted to us. We are counting on every beat of the heart for our survival, and we should give thanks, with every beat, for what an incredible gift we’ve been given.

References

1. Bui, A. L., Horwich, T. B. & Fonarow, G. C. Epidemiology and risk profile of heart failure. Nat Rev Cardiol 8, 30-41 (2010).

2. What Is a Ventricular Assist Device? NHLBI, NIH. Retrieved from www.nhlbi.nih.gov/health/health-topics/topics/vad/ on 1/2/14.

3. Ventricular assist devices (VADs) Definition – Tests and Procedures – Mayo Clinic. Retrieved from www.mayoclinic.org/tests-procedures/ventricular-assist-devices/basics/definition/PRC-20020578 on 1/2/14.

4. Artificial Hearts. Retrived from www.umasswiki.com/wiki/Artificial_Hearts on 1/2/14.

5. Artificial heart. Retrieved from en.wikipedia.org/wiki/Artificial_heart on 1/2/14.

6. Heart Assist Devices. Texas Heart Institute. Retrieved from http://texasheart.org/Research/Devices/index.cfm on 1/12/14

7. Carmat artificial heart patient in good condition: hospital. Retrieved from www.reuters.com/article/2013/12/30/us-carmat-patient-idUSBRE9BS07O20131230 on 1/2/14.

8. Lu, Tung-Ying, Bo Lin, Jong Kim, Mara Sullivan, Kimimasa Tobita, Guy Salama, and Lei Yang. “Repopulation of decellularized mouse heart with human induced pluripotent stem cell-derived cardiovascular progenitor cells.” Nature communications 4 (2013).

9. Heart of genetically modified pig ‘successfully transplanted into monkey’, South Korea scientists claim. Retrieved from http://www.dailymail.co.uk/news/article-2164964/South-Korea-scientists-successfully-transplant-heart-genetically-modified-pig-monkey.html on 12/1/14

10. Pig to human transplants. Retrieved from http://www.theguardian.com/world/2002/jan/03/qanda.simonjeffery on 12/1/14

Open heart surgery is performed after putting the patient to sleep under a general anesthetic. The chest is then opened by the surgeon, and the heart is temporarily bypassed or deactivated for the duration of surgery (although in some new techniques like beating heart surgery or minimal invasion heart surgery, the operation is possible without deactivation of the heart) During this period the functions of the heart are performed by an artificial lung mechanism called the heart-lung machine (cardiopulmonary bypass machine). Performing surgery on a working heart cases where there is no facility for beating heart surgery would be like trying to repair the engine of a car while it is in motion. This is why it is necessary to temporarily prevent the functions of the heart during the operation, which requires great care and accuracy.

Stopping the heart

During this procedure the patient is connected to the machine, thin pipes called cannulae are inserted into the main veins which lead to the heart, and thus the blood which goes to the heart is directed into the heart-lung pump, fed with oxygen, and then redirected into the body. Preventing the function of the heart is not a very difficult process. When the heart-lung machine is activated and the blood is cooled and redirected into the blood vessels, the body temperature is reduced to below 30°C, and this lowers the heart rate and assists the heart to stop functioning. The actual stopping of the heart is performed by feeding a serum containing a concentrated solution of potassium ions into the coronary artery, which feeds the heart muscle. Potassium ions are normally found in the human body but in a fixed proportion; potassium is an electrolyte which, if increased, causes a defect in the heart’s rhythm and can lead to ceasing of the heart function. Feeding the coronary artery rapidly with a rich potassium solution causes the heart to stop within a few seconds and allows the surgeon to perform the operation on a non-functioning, motionless heart.

The heart should not be stopped from functioning for a long period, even if the heart-lung pump is performing the function of the heart successfully. Under normal conditions the pump cannot perform the whole duty of the actual heart and lungs. When the body temperature is reduced, there is a reduction of functioning in many organs of the body to such an extent that they almost stop working, especially the brain. This means that every organ freezes and if the patient’s pulse were taken within this period, they would be assessed as dead.

Restarting the heart

To restart the heart following the operation a reversal of the procedure performed at the beginning of surgery is necessary; the temperature of the body is increased to 36.5–37°C again with the help of the heart-lung pump, and at the same time the amount of potassium in the blood is reduced to a normal level. This is usually executed by ensuring the normal function of the kidneys which discard the potassium from the body. This is when the function of the heart is monitored closely because there is a reversal in the process of inducing low body temperature and the excess of potassium which caused the heart to stop. In other words, the barrier which stopped the flowing river is removed; therefore, according to the laws of physics, the trapped fluid should flow again at great speed, and although following surgery the majority of hearts do begin to function again when these procedures are performed, there is unfortunately no actual guarantee. There may be certain complications or even causes which we have not yet discovered, in which case an electric shock of 10–20 joules is delivered directly to the heart muscle to encourage it to function normally. If this is unsuccessful, medication such as adrenalin, which induces the functioning of the heart, is given to the patient. If, following these repeated procedures, there is no effect, and, regardless of all the effort, the heart does not function, then everything is performed again from the beginning, including the operation. But there is always the possibility that the desired result may not be achieved. Human beings always face the prospect of death in daily life, and although there is a very slim chance of death, with such a big operation there is always the possibility.

The result

We are normally totally unaware of the rhythmic incidents, a combination of great harmony, occurring within our bodies. Even breathing, a necessity for every living creature to stay alive, is not an action which we activate and continue of our own will. Sight, hearing, hunger and senses are acts of nature over which we have little direct will or power. Nevertheless, they are all events which we can only describe as divine miracles and what a great blessing it is that none of these complex functions of our bodies have been left to us humans.

When you were a mere nineteen-day embryo, my creation began from a special mass of cells. At first, I looked like a tube, then I twisted, turned, and gradually the creation of my chambers and my neighboring veins began. Together with the other cells of the body, we developed to serve as different parts, such as nerves, skin, cartilage, muscles, and so on. And the cells which make me up are very specially programmed. When they reached a certain number and mass on your twenty-second day, they were commanded to march, and only God knows for how long. When all my cells contract together to beat, you feel it as your pulse. Though I operate in your body, Peter, you do not think much about my beats, but when you run fast, I just have to beat faster for your legs require more blood. Only then, Peter, do you notice me, but you do not give me a second thought anyway. You are so heedless, as if I will carry out this duty forever and will never get tired. Let us admit that is not so unusual for a young man, but the worst is you do not ever think of who blessed you with such a gift, and that really makes me sad. Nowadays you go to high school, and there they occasionally talk about me in biology lessons. Peter, you are not to blame, actually-teachers talk about me as if I were a simple pump. However, you cannot even move a finger if I do not pump blood into your brain. But today, I will let you know that I am not just a simple mass of flesh. I am going to tell you today that you should care about me both physically and spiritually, otherwise, you will truly regret it. I am just a friend, warning you about the bitter truth; you still have a chance to make it up.

All the cells, the building blocks of your body (maybe 100 trillion of them) need me for their nutrition, breathing, digestion, waste disposal, and to carry out their particular duties. You wonder why? Well, all their needs are met thanks to my being created to work ceaselessly. This is why I start working before any other organ at the embryonic stage. Even I do not know how long exactly I will work; sometimes, in spite of being in sound health, the appointed hour comes and I leave my duty obeying the divine command. For the most part, the Angel of Death does not tell me to stop for no reason-he somehow uses an apparent cause. There are so many causes to make me leave my duty, in such an age where accidents, bad habits, and suicides are tremendously high.

In fact, even I marvel at how I work. I am equipped with certain precautions against blood losses which occur as a result of injuries, but if the blood loss is not made up for and the bleeding is not stopped, I may get tired and stop functioning after a certain time. I can be easily affected by certain types of poisoning. This does not matter much, but what really upsets me is your living irregularly, unhealthy eating habits, inactivity, laziness, and especially your leading a stressful life quarrelling with everyone. I endure these for a while, but sometimes when I cannot take it anymore, I just quit or pretend to quit in order to draw your attention. Right after that, you have people screaming, calling the doctor in panic, demanding pills, adrenalin or heart massage… All of these are fine my dear, but why on earth do you wait until I become like that! Listen, Peter, I am telling you again, it is you who does me the greatest harm. So do not be offended if I one day get tired and quit! You just keep gulping down fatty foods, my downstairs neighbor, the stomach, keeps complaining that you are filling it up too much. When it is filled up, it starts putting pressure on me naturally. Haven’t you heard about the hadith counseling people to leave one third of their stomach empty and rise from the table before they are full? I can understand the vegetables, but what about the fast food, fried things, and other unhealthy stuff you eat? Be careful, you will have to pay for it before long, and it will be too late. Well, one has the right to benefit from the blessings in this world, but one should know where to stop. If you go on like that, my valves will be disabled by fat and my main arteries will be clogged. As for my coronary arteries, they are already created narrow and they can be clogged in a short time and lead to a heart failure.

You are just a couch potato lying before the TV all day without moving at all. I would not be surprised if you started going to the corner shop by car. If only you did exercise for a little part of the day. Some of your friends do the daily prayers and kill two birds with one stone. They fulfill their duty to their Creator and relieve their hearts with the bodily exercise. In addition, their hearts are at ease thanks to their faith. Another welcome relief for us is their fasting for a whole month once a year. Staying hungry for a certain part of the day comforts me and gives me a chance to burn some fats.

The muscle tissue which makes up my main structure is designed as an intricate ball of fibers and so I am able to function properly without changing my shape too much as I contract and relax. The surface of my walls is wrapped up in a double layer in order to prevent harm from rubbing against the ribs, which are set around me as a protective cage. Also, there is a special liquid between the two layers of the membrane and this lowers the friction even further. C’mon Peter! Who can arrange so many precautions so splendidly?

Like car engines with four cylinders, I also work like a pump with four chambers. My upper chambers are called atriums. The one on the right takes in the waste-rich venous blood, and the one on the left takes in the oxygen-rich arterial blood. The muscular strength of these chambers is relatively low, but it is good enough to pass the blood they take to the lower chambers. As for my lower chambers, named ventricles, they have thicker walls and stronger muscles. They are given the ability to contract and pump blood with great pressure. Moreover, the lower chamber on the left has even stronger muscles and thicker walls since this very chamber enables me to send blood to the entire body with great pressure and speed. Thanks to the large vein named the aorta, I send blood to each organ in the required amount and at the right speed. Precise timing is vital for my four chambers to contract successively, to open of the valves at the exact moment they should, and to send blood to the neighboring chamber or to the two main arteries. The closing of the valves also requires perfect timing to prevent the blood from flowing back. The coordination of this timing mechanism is obtained through the regular production of electricity by the atrioventricular bundle. If there is something wrong with the timing of my valves, or if they cannot close properly because they are blocked with fat or calcification and so let blood leak, you diagnose this situation as a disease. As a precaution against blood flowing backwards through the valves between the atriums and ventricles under heavy pressure, some cords are tightly fixed under them. You are not aware of any of these, but I keep working even when you are asleep. Naturally, I may change my speed at different times, according to what you do. While you are asleep, I work at an easier tempo. I work faster than normal while you are running or doing heavy exercise and I send the necessary amount of blood to every organ. My energy source? Well, the fuels I mostly make use of are fatty acids, lactic acid, and sugars. In addition, thanks to my special metabolism, I never get tired. There is only a very short period of rest of one tenth of a second between every contraction and relaxation I make. The stimulating command must come with perfect precision so that all my muscles start to contract and relax simultaneously and so that I can generate an efficient pumping force. Actually, I am not quite sure how this timing is arranged during different activities. A tiny automatic center on me produces electrical signals; the activities of upsetting and then resetting the ion balance inside and outside the cells in order to produce these signals is carried out with reactions happening in a time as short as one thousandth of a second. Even though these cells make me work with the electricity they produce, I am not really independent. The foremost among the factors that affects my functioning is the nerves from the brain. Therefore, the fear, anger, and sadness you experience upset my functioning as well. This must be why people have taken me as the center of emotions; although anger and sadness take place in the brain, I was located as the emotional center, as the effect surfaced in me.

Peter, I will ask you a simple question: is there some engineer who made the TV set you lie before? Are there people who write the articles in the magazine you are holding or who lay out the letters and pictures? There are some agents right? So, more perfectly than all of these, should there not be One who has created me and my system of blood vessels, and then placed me in your chest cavity? Well, it is high time you switched off that TV set. Now Peter, just as I fulfill my duty regularly to keep you alive, you should also spare just ten minutes to pray for and praise your Lord Who has created your body so perfectly. In the meantime, I will have found a chance to get rid of the strain you put me under because of your hurry and stress.

Within these few pages, I have probably told you only a thousandth of my splendid structure and the precision of my functioning. Neither I, nor physicians have the proper knowledge to explain all about me completely. So, my friend Peter, you need to learn to say, “How beautifully it has been made,” instead of “How beautiful it is.”