Living with heart failure. What are LVAD?

Left ventricular assist device (LVAD) systems relieve the inefficient ventricle from pumping blood. LVADs are used as a “bridge” to heart transplantation, and even to recovery or remission of ailments, or as a target treatment. By supporting the circulation, they improve the comfort and quality of life of patients, and are an invaluable aid in the case of end-stage heart failure, cardiogenic shock, and a mechanical complication of myocardial infarction.

1. According to epidemiological data, an increasing number of patients suffer from heart failure (NS). In Poland, nearly a million people live with the diagnosed disease
2. It is estimated that in 20 years this number will increase by another 250. Unfortunately, the prognosis of heart failure is poor and is associated with high mortality, especially after the age of 65

According to the recommendations of the European Society of Cardiology (ESC), transplantation is the treatment of choice in end-stage heart failure. However, in Europe, only 600 heart transplants are performed annually, and the number of patients with severe, drug-resistant HF is growing rapidly. About 1200 patients are qualified for heart transplantation each year. Therefore, mechanical support of the heart, as a well-documented method of treating severe heart failure, is gaining more and more importance.

Cardiovascular system – where does the blood flow? 

How do the ventricular support systems work? It is impossible to explain their mechanism and meaning without basic knowledge of the physiology of the circulatory system.

The circulatory system (cardiovascular system) is made up of a closed system of blood vessels (arteries, veins and capillaries) and the heart muscle. Its job is to transport blood. The heart plays a special role here – the pump that forces the blood to circulate. Thanks to the cardiovascular system, all body tissues are supplied with life-giving substances (e.g. oxygen). In addition, blood drains the cells of metabolism by-products (including carbon dioxide).

The cardiovascular system consists of large (systemic) and small (pulmonary) circulation. In the systemic circulation, blood is distributed from the heart “to the circuit” – throughout the body. High circulation depends on the left ventricle, which acts as a vigorous pump in it. Blood (during contraction) is ejected from the left ventricle – it goes to the elastic aorta and flows through the muscular arteries to the organs. The arteries divide into smaller and smaller vessels – tiny arteries and arterioles, until they turn into capillaries made of a single layer of endothelial cells. An important process takes place in inconspicuous blood vessels: substances are exchanged between blood and tissue fluid. The blood captures the connections she brought and begins to “seek” a way back. The capillaries merge and smoothly form lines that create ever-larger veins. Through the main veins, the deoxygenated blood returns to the heart, or more precisely – to the right atrium.

Another pump plays a key role in the small (pulmonary) circulation – the right ventricle. Thanks to it, blood is pumped into the so-called a pulmonary trunk that branches into the right and left pulmonary arteries. And these – dividing into smaller vessels – carry blood to the right lung and the left lung. Already oxygenated blood flows from the lungs and returns to the heart. This time it flows through the pulmonary veins to the left atrium.

The heart – the pump that moves the blood 

It can be said that the heart consists of two separate muscle pumps: right and left, which consist of the atrium and the ventricle (separated by a valve). Blood flows into each pump through the veins and out through the arteries, previously crossing the crescent-shaped valves that prevent the blood from flowing back to the heart.

The left ventricle is a pressure pump, the right ventricle is a volumetric pump. Interestingly, the left ventricle also affects the emptying of the right ventricle. How? During systole, the interventricular septum inverts into the right ventricle, pushing out blood.

The heart pumps blood into its vessels by continually, repeating cycles of filling and emptying its cavities.

All the phenomena that occur in the heart from the beginning of one contraction to the beginning of the next contraction constitute the so-called cardiac cycle. The amount of blood that the heart pumps into the aorta during one cycle of the heart is called the left ventricular ejection fraction (stroke volume). On the other hand, the volume of blood that the heart pushes into the vessels in one minute is called cardiac output (or minute capacity).

Devices supporting the functioning of the ventricles of the heart 

Devices for mechanical heart function support are divided into 3 basic groups:

1. counterpulsation devices,
2. ventricular support devices
3. artificial hearts

Ventricular assist devices include pumps that support or save the heart’s ventricle. VADs can support the work of the left ventricle, right ventricle, or both. They are used both for short-term heart support (e.g. after a heart attack, after cardiac surgery) and as long-term therapy in advanced heart failure in patients waiting for a transplant.

Right ventricular systems support pulmonary circulation, and left ventricular (LVAD) systems support peripheral circulation. The use of LVAD allows tissues and organs to be supplied with blood, even if the projection of the ventricle (right or left) is severely limited.

The introduction of VAD requires access to the heart by:

1. · Sternotomy – longitudinal incision of the sternum
2. · Mini-thoracotomy – a small lateral incision in the chest

There are also modern rotary pumps that can be implanted through the blood vessel route. Classic implant systems are usually placed under the skin of the abdomen, sometimes inside the chest or abdominal cavity. Extracorporeal pumps are located outside the patient’s body (close to the patient, e.g. on the front surface of the abdomen).

Rotary pumps 

Among the devices for supporting ventricular functions, there are rotary and pulsating pumps.

Rotary pumps ensure continuous blood flow due to the movement of a special rotor. These include centrifugal centrifugal pumps and systems for extracorporeal transmembrane oxygenation, called extracorporeal membrane oxygenation (ECMO) systems.

Traditional rotation systems have been used in medicine for decades (the history of ECMO dates back to the 70s). Their service is not complicated, and they are also not particularly expensive solutions. However, patients with a classic rotary lobe pump require intensive supervision in a hospital setting.

Currently, new, miniaturized and much more expensive centrifugal pumps are being developed and tested, placed inside the chest, sometimes even implanted in the pericardial sac (where the heart is located). These types of pumps are intended for long-term heart support at home.

In the latest devices, the rotor is suspended between the magnets, which minimizes the resistance to work. The systems consist of a metal cannula that is inserted into the left ventricular cavity through an opening in the apex of the heart. A drainage cannula is placed in the aortic wall. The pump (connected to the inflow cannula) is implanted directly into the heart (it is placed in the pericardial space). The only moving part of the pump is the impeller which causes the blood to flow. The power supply leads a thin control cable, which runs through the skin of the abdomen to a special controller (the patient wears it directly against the body).

One of the most modern devices of this type is the HeartWare HVAD – XNUMXrd generation heart support pump.

Pulse pumps – pulsating blood flow 

In addition to rotary pumps, ventricular assist devices (VADs) include pulsed (pneumatic and electromechanical) pumps that produce pulsatile blood flow. These include models designed for:

1. medium-term ventricular support (ABIOMED BVS 500, POLCAS);
2. long-term ventricular support (also fully implantable).

Pulse systems for long-term support are intended for home use (patients are discharged home after hospitalization and training in operating the device). However, regular check-ups are necessary at the VAD implantation center (constant cardiac and cardiac surgery care).

The training should include, inter alia, pump operation (including battery replacement), how to respond to device alarms, event reporting and contact with the treatment center. Knowing how to change the dressing is very important. One should not forget to operate an INR device at home. The blood clotting index must be monitored in patients treated with anticoagulants (drugs that “prolong” blood clotting).

Ventricular support – short, long, permanent? 

VAD (Ventricular Support) is used to:

1. short-term support – up to 7 days (eg ECMO and rotary pumps supporting the functioning of the right or left ventricle);
2. medium-term support: from 7 days to 3 months (pulse pumps, some centrifugal pumps);
3. long-term support (for months, years or permanently), including:
4. partially implanted devices (e.g., Novacor, HeartMate, MicroMed DeBakey, Jarvik 2000, Berlin Heart INCOR);
5. fully implantable devices (artificial heart, eg ABIOCOR).

The Polish pneumatic pump POLCAS, intended for short-term or medium-term support of one or both ventricles, can boast the longest history in our country. The solution was used in over 200 patients.

Two FDA-approved devices with CE (Conformité Européenne) marking dominate the long-term treatment:

1. HeartWare pump,
2. pump HeartMate 3.

The HeartMate 3 pump replaces the earlier HeartMate 2 (continuous flow in-line pump). The HeartMate 3 partially simulates a pulsating flow by increasing the speed periodically. Why is it so important?

Implantable circulatory support models usually provide continuous blood flow. Meanwhile, the natural blood flow is pulsatile, which determines the proper function of the endothelium of blood vessels. Continuous flow is believed to be responsible for the distant complications of VAD (e.g., hemorrhagic, thromboembolic). That is why so much hope is associated with the latest generation III pumps, in which the flow speed changes every 2 seconds, giving “pulsation” – imitating the natural blood flow in the human body.

LVAD – optimistic research results 

Recent years have been a time of increasing use of long-term left ventricular support (LVAD) systems. The technical parameters of the devices are constantly being improved, the reliability of the pumps increases, and their ergonomics. Therefore, in the decision-making medical circles there are already discussions about the possible extension of indications for such therapy.

Optimism is caused by, among others the results of the ROADMAP study (two-year follow-up), which suggest that the extension of indications and earlier LVAD implantation contributes to a significant improvement in the quality of life of patients. It does not increase mortality or the number of adverse events (compared to patients treated pharmacologically).

For the sake of order, it should be noted that ROADMAP is a study without randomization (randomization is the random allocation of patients to 2 groups: experimental and control). Randomized trials are considered to be the most reliable; their results are of particular importance in EBM (evidence-based medicine) – medicine based on scientific evidence. A well-designed randomized trial could contribute to the dissemination of LVAD. Of course, the price is also a barrier, but systems manufactured in Poland will most likely be less expensive.

LVAD and BiVAD – when and for whom? 

American cardiological societies (American College of Cardiology / American Heart Association; ACC / AHA) already in 2009 suggested implanting pumps for mechanical circulatory support in severe form of heart failure, resistant to pharmacological treatment.

The European Society of Cardiology (ESC) identified for the first time the clinical situations in which implantation of left ventricular (LVAD) or dual ventricular (BiVAD) assistive devices could be considered in guidelines published in 2012.

The 2016 European Society of Cardiology (ESC) guidelines for the diagnosis and treatment of heart failure are currently in force.

The indications for LVAD implantation are, inter alia, severe symptoms of heart failure that persist for more than 2 months, despite the implementation of optimal pharmacological treatment and implantation of a cardioverter-defibrillator or the use of resynchronization therapy. LVAD is considered in patients who have at least one additional factor:

1. significant reduction in left ventricular ejection fraction (less than 25%);
2. at least three hospitalizations for heart failure in the last 12 months with no immediate cause identified;
3. addiction to an intravenous inotropic drug (regulating the strength of contraction of the heart muscle);
4. progressive organ (kidney, liver) dysfunction due to reduced blood flow;
5. no right ventricular dysfunction with severe tricuspid regurgitation.

In selected patients with end-stage heart failure who meet these criteria, implantation of a device to assist left ventricular function or both ventricles is recommended. In patients eligible for heart transplant, therapy may reduce the severity of symptoms and lower the risk of hospitalization for heart failure. In such cases, LVAD also reduces the risk of premature death while waiting for a transplant.

Patients who are not eligible for heart transplant should also consider such surgery.  

Mechanical circulatory support – indications 

An indication for the use of mechanical circulatory support (MCS; mechanical circulatory support) is, among others cardiogenic shock and acute heart failure. MCS is also recommended in end-stage heart failure in patients who are ineligible for heart transplants or who have very long waiting times for a transplant. In these cases, mechanical left ventricular support (LVAD) is used for long-term cardiac support or as a targeted therapy.

Contraindications to the use of mechanical circulatory support are bleeding, severe sepsis, recent stroke and severe head trauma. It is also not used as a bridge treatment in patients for whom heart transplantation is not contraindicated. Complications include bleeding, thromboembolic events, renal failure, infections, and haemolysis. The device may also be damaged.

The effectiveness of mechanical ventricular support depends on the cause of the heart failure. However, it is estimated that thanks to VAD, even 70 percent. patients will receive a transplant. The method saves 75 percent. patients after acute myocardial ischemia (myocardial infarction) complicated with shock. Good results of the therapy are also observed in the group of patients with fulminant myocarditis.

Initially, the results of long-term VAD use left much to be desired (only 20 percent of patients survived 2 years). However, the world does not stand still – thanks to the progress of medical technology, the implementation of innovative solutions and the experience of doctors, the survival rate is increasing, and the number of complications is significantly decreasing. Today, 80-90 percent of patients survive after implantation of mechanical assist systems.

Mechanical circulatory support in Poland 

In clinical practice, mechanical circulatory support appeared as early as 1953. It was then that extracorporeal circulation was used for the first time. The moment turned out to be a breakthrough – it inspired to search for and develop new surgical methods of treating heart diseases. He laid the foundations for, inter alia, for modern circulatory support systems.

In 1967, counterpulsation was used for the first time with the use of an intra-aortic balloon pump, supporting the circulation in acute heart failure.

In our country, artificial heart chambers (created by prof. Religa) began to be implanted in 1999. In the following years, the method developed dynamically; technological advances concerned mainly mechanical devices supporting the work of the left ventricle (LVAD; left ventricular assist device). Over time, pumps with pulsating and then continuous flows, axial pumps and new centrifugal pumps, fully implanted into the pericardial sac, with rotors levitating in the electromagnetic field appeared. The brilliant solution eliminated areas not washed by blood (present in earlier models) that contributed to thromboembolic complications.

Mechanical heart support systems have been developing particularly intensively in the last two decades. It may not seem like much. However, in interventional medicine this is a real era. Subsequent scientific reports on the promising results of LVAD application raise new hopes. In view of the low availability of organs for transplantation and difficulties in the pharmacological treatment of heart failure, it can be assumed that the future belongs to LVAD.

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