Overview of Cardiac Resynchronization Therapy
Heart failure, a serious health condition where the heart doesn’t pump blood as well as it should, is a significant cause of illness and death globally. It often leads to a lower quality of life, reduced life expectancy, and adds financial stress to the healthcare system. A common cause of heart failure is an issue with how well the left ventricle (one of the heart’s main pumping chambers) works.
Medical advances in the last 30 years have improved survival rates for people suffering from a specific type of heart failure, where the heart pumps out less blood than normal. Nevertheless, the chance of becoming ill or dying due to heart failure remains high.
With more people living longer and improved treatments for heart-related diseases, the number of people with heart failure is growing. This poses significant challenges in managing irregular heartbeat (cardiac arrhythmia) and severe heart failure.
A condition known as electromechanical dyssynchrony, where there’s a delay in the transmission of electrical signals causing the heart muscles to pump out of sync, often happens in people with reduced blood ejection from the heart. This inefficiency can cause other issues like the worsening of mitral regurgitation (a condition where the heart’s mitral valve doesn’t close tightly, causing blood to flow backward in the heart) and adverse changes in the shape and function of the left ventricle. This often leads to poor health outcomes.
In the early 1990s, experts recognized that issues with the synchrony of heart muscle contractions played a significant role in heart failure. They found that devices could stimulate different parts of the heart at the same time to make up for this out-of-sync condition and electrical delay. It was in the late 1990s that the effectiveness of this ‘multisite pacing’ was first reported in humans, leading to the development of a treatment called Cardiac Resynchronization Therapy (CRT). This therapy uses artificial electrical stimulation for heart failure — it was the first of its kind.
Since then, CRT has become a crucial treatment method for heart failure patients with reduced ejection fraction. CRT devices are implanted and mainly focus on biventricular pacing, which stimulates both of the heart’s main pumping chambers, bringing about a more synchronized heartbeat. This document reviews the use, conditions suitable for CRT, potential complications, and the important role it plays in heart failure treatment.
Anatomy and Physiology of Cardiac Resynchronization Therapy
The coronary sinus is an important part of the heart’s system of veins. It’s situated in the back area of a groove situated between the two main chambers of the heart (the atria and the ventricles). The coronary sinus is created where the great cardiac vein merges with the main back and side vein. Other important veins that link to the coronary sinus and help drain blood from the back part of the left main chamber of the heart, referred to as the left ventricle. The middle cardiac vein is the biggest vein connecting to the coronary sinus, and it also gets blood from the front veins, as well as from the walls separating the chambers of the heart.
When the function of the left ventricle decreases, it triggers certain chemicals in the body, leading to changes in the heart’s shape and size – a process known as remodeling and dilation. This is common in people with heart diseases related to the heart’s muscle, known as cardiomyopathy. Many of these patients also have delays in the electrical signals in the heart that control the timing of the heartbeats. This causes what is known as electromechanical dyssynchrony, meaning that different parts of the heart are not working together as they should.
This lack of coordination in the heart’s contractions leads to uneven burden on different areas of the heart, with the parts that are activated earlier bearing less load, and those activated later bearing more load. This sequence results in a decrease in the amount of blood the heart can pump out efficiently. The impact of this is much worse when the differences in timing of muscle activation are more noticeable. All of this makes heart failure more complex and severe. But there is a characteristic feature of cardiac resynchronization therapy (CRT) that can improve this. CRT coordinates the contraction of the heart chambers, thereby improving the overall performance of the heart by increasing the amount of blood it can effectively pump.
Why do People Need Cardiac Resynchronization Therapy
A biventricular pacing device, also known as Cardiac Resynchronization Therapy (CRT), is a type of pacemaker that’s used to help your heart beat more normally. Doctors suggest using CRT for several types of patients based on certain heart conditions and symptoms. This works like a system that sorts the level of recommendation into different categories (class I to class IIb).
A Class 1 recommendation (which means it’s strongly recommended) for a CRT would be for patients who have:
- A low heart pumping strength (less than 36% – this is also known as “Left Ventricular Ejection Fraction”)
- Normal heart rhythm but with an interruption in the electrical impulses that control the heart’s pumping action (also known as “Sinus Rhythm with Left Bundle Branch Block (LBBB) morphology”)
- A long time taken for the electrical signals to travel across the heart (longer than 149ms – known as “QRS Duration”)
- Heart failure symptoms that affect daily life, requiring medical treatment (also known as “New York Heart Association (NYHA) class II, III, or ambulatory IV symptoms”)
- Good overall health, outside of the heart condition.
Class IIa recommendation (which means it’s reasonable to use CRT) would be for patients who match the conditions above, but with a QRS duration of 120 to 149ms or are dealing with a different pattern of heart electrical interruption (non-LBBB pattern).
There is also a suggestion (Class IIb, which means CRT may be considered) for those who have a low heart pumping strength, require a pacemaker for something else and will end up needing the majority of heartbeats to be paced. All of these recommendations require the patients to have acceptable non-cardiac health, which means the rest of the body should be generally healthy to tolerate the implantation and operation of a CRT device.
When a Person Should Avoid Cardiac Resynchronization Therapy
Cardiac resynchronization therapy (CRT) is a treatment used in heart-related conditions. There aren’t any total blocks or ‘absolute contraindications’ for this therapy when it is suitable for the patient.
However, there are some situations, or ‘relative contraindications’, where this therapy might not be the best choice:
- Dementia, a chronic disorder that affects memory and thinking
- Advanced cancer that requires end-of-life care
- Chronic illness with a life expectancy of less than one year
- Acute decompensated heart failure, a sudden worsening of the symptoms of heart failure
- Active infection or sepsis, a life-threatening response to infection
- Coagulopathy, a condition that affects the blood’s ability to clot.
Ultimately, the decision to use CRT will depend on the individual’s overall health and their specific condition.
Equipment used for Cardiac Resynchronization Therapy
To place a device that helps both sides of your heart beat together, known as a biventricular pacing device, doctors need specific equipment.
The heart procedure is generally conducted in a special room in the hospital called a cardiac catheterization laboratory. This lab is equipped with fluoroscopy (detailed X-ray machine) and hemodynamic monitors (machines that display your heart’s vital signs).
An ultrasound machine is also necessary to help doctors see inside your body and place the device correctly.
The procedure requires other tools as well, like needles and sheaths (tubes to guide the inserting instruments), the pacing leads (wires that connect the device to your heart), and the generator (the unit that regulates the electrical impulses).
The doctor will also need a device programmer, used to adjust your device’s settings after it has been implanted. The settings will be personalized to best suit your heart’s needs.
Lastly, sutures, or stitches, will be used to close the wound after the procedure.
Who is needed to perform Cardiac Resynchronization Therapy?
The biventricular pacing device, often used to improve your heart’s rhythm, needs a team of healthcare professionals to successfully implant it. This team includes a cardiac electrophysiologist, who is a heart doctor specializing in heart rhythms. Also crucial to the procedure is the cardiac catheterization laboratory technician who translates the medical images into information the doctor can use, and an electrophysiology technologist who controls the device’s programming.
The nursing staff on hand will make sure you’re comfortable and provide necessary medications during the process. An anesthesiologist, a doctor who manages pain and puts you to sleep during the procedure, will also be present to ensure your comfort.
In some cases, if it’s not possible to place a part of the device (called the epicardial left ventricular lead) through a tiny incision in the skin (percutaneously), a cardiac surgeon might also be needed. This specialized doctor can safely place this piece directly on the heart (epicardially) if need be.
Preparing for Cardiac Resynchronization Therapy
Before a heart catheterization procedure, there are several steps patients need to go through to prepare.
First, the doctor carefully assesses the patient’s condition to make sure they are fit for the procedure. They explain the procedure in detail, including the benefits, risks, and possible complications it might have. This thorough briefing ensures the patient understands what they are about to undergo.
Blood tests are done before the operation to check how the blood clots, which is a relevant factor during the operation. It’s especially important if the patient is taking drugs that act as blood thinners or anticoagulants.
Patients are asked not to eat or drink for at least six hours prior to the procedure. This is called fasting and is necessary for safety reasons during the procedure. The hospital staff will place a tube into a vein (an intravenous cannula) to give fluids and medicines. As a preventive step against infections, antibiotics are given that can fight against staphylococcus, a common group of bacteria.
On the day of the procedure, once the patient arrives in the catheterization lab, the area on the body where the doctor will insert the catheter is cleaned with an antiseptic solution to kill any germs and then covered with a sterile sheet.
Before the procedure starts, the patient gets medicine to make them relaxed and ensure they are comfortable (sedation). A local anesthetic, which is a drug that numbs a small area of the body, is applied at the site where a small incision will be made. This minimizes discomfort during the procedure.
How is Cardiac Resynchronization Therapy performed
The technique to implant a CRT (Cardiac Resynchronization Therapy) device, which helps coordinate your heart’s rhythm, has developed a lot since it was introduced in the early 1990s. At first, doctors had to cut into the chest wall to have access to the heart, but now, the procedure can be completely performed through the veins, thanks to improved delivery systems.
The method chosen to reach the heart depends on the personal preference of the surgeon. The veins commonly used for this procedure are the subclavian vein (located under the collarbone), axillary vein, and cephalic vein. The cephalic vein, located in the upper arm, is usually the first choice, followed by the subclavian vein. Yet, using the subclavian vein can sometimes lead to complications like a collapsed lung, and this method may make future procedures challenging.
The implantation of a CRT device involves placing three leads or wires (in the right atrium, right ventricle, and left ventricle of the heart). In a CRT-D (a CRT device combined with a defibrillator), three wires are placed in the vein, and then a large catheter, or tube, is used to guide the placement of these leads. The defibrillator lead is first positioned in the right ventricle of the heart. Once the leads are all in the proper place, the sheaths are removed, and the leads are secured by stitching onto the chest muscle.
For a CRT-P device (a CRT device without a defibrillator), two wires are placed in the vein. Then, just like the CRT-D, the placement of the leads is guided by fluoroscopy, an imaging technique that uses X-rays to obtain real-time moving images. The wires are connected to the device, which is placed in a space made under the skin in the chest area.
To achieve the best heart rhythm coordination, the lead placed in the left ventricle of the heart needs to be positioned in a specific area. If it’s too far down in the ventricle, the outcomes may not be as good.
Placing the lead in the right place can sometimes be difficult due to the twisted nature of the blood vessels. If this happens, your doctor might use different tactics, like changing the angle of the catheter or using different sizes of leads. In some cases, a stent (a small tube that helps keep arteries open) might be used to help stabilize the lead.
After the device is placed, your doctor will need to program the device to ensure that it’s synchronized with your heart’s rhythm for maximum benefit. This process is called CRT programming, which helps coordinate the contractions of your heart chambers, helping it pump more effectively. However, the techniques used for this programming and their impact on the CRT success is still a topic of debate among medical professionals.
Possible Complications of Cardiac Resynchronization Therapy
When a CRT (cardiac resynchronization therapy) device is implanted, there can be some complications. Here are some of the major ones:
1. Bleeding at the site where the CRT device is put in and pocket hematoma, which is a collection of blood outside of a blood vessel. Clinical trials have reported this to happen in up to 2.5% of cases. However, in actual day-to-day medical practice, this may be seen more often as only those that needed treatment were reported in clinical trials. If a pocket hematoma develops early on and needs treatment, the chances of infection around the device increase.
2. Lead dislodgement: CRT trials have shown dislodgement or the slipping of the lead, a conductor delivering electrical current from the CRT device, happening in 2.9% to 10% of patients. The lead placed in the left lower chamber of the heart (ventricle) is more likely to slip than the leads in the right upper chamber (atrium) and right lower chamber (ventricle).
3. Infection: This is a major challenge with CRT and other implanted heart devices. Infections involving the CRT device have been reported in up to 3.3% of patients. Men, patients with previous device-related infections, and those who have had a device re-implanted are more prone to such infections.
4. Pneumothorax: This is a rare complication, seen in up to 0.66% of patients. This is a condition where air leaks out of the lungs into the chest cavity, and it is more common in patients with a subclavian access (a type of vein used for device implantation), a history of severe lung disease (chronic obstructive pulmonary disease), those older than 80 years, and during re-implantation. Using another access route known as the cephalic vein cut-down technique can help avoid this complication.
5. Coronary sinus perforation/dissection: This is a rare but recognized issue where a coronary vein gets a tear during the placement of the left ventricular lead during the CRT device implantation. It is seen in up to 0.28% of patients and these patients tend to stay longer in the hospital after the procedure.
Other complications can include cardiac tamponade (serious condition with fluid accumulation in the sac surrounding the heart), injury to the heart muscle, breakage of the lead, pocket erosion (skin break down at the implant site), and stimulation of the phrenic nerve (a nerve that controls the diaphragm, the major breathing muscle). Inappropriate phrenic nerve stimulation happens in up to 13% of patients during the placement of the left ventricular lead and it’s more common at certain locations such as mid-lateral, mid-posterior and apical sites.
What Else Should I Know About Cardiac Resynchronization Therapy?
As the population gets older and more people survive heart attacks, heart failure has become increasingly common. Heart failure is a serious medical condition where the heart does not pump blood around the body properly. Medications such as ACE inhibitors, angiotensin receptor blockers, beta-blockers, aldosterone antagonists, and ARNI (angiotensin receptor neprilysin inhibitor) are used to manage and improve the condition for most patients.
However, despite these treatments, some patients still suffer from poor health outcomes and require a different approach. A common form of treatment in these cases is a device-based therapy called Cardiac Resynchronization Therapy (CRT). This treatment device helps by encouraging your heart to beat more efficiently, which can greatly improve survival rates.
Apart from its lifesaving potential, CRT can also enhance the quality of life, decrease hospital stays, and improve physical capabilities like maximum oxygen uptake, especially in patients with severe heart failure. The choice for using this therapy is carefully considered, taking into account factors like the patient’s specific health status and seriousness of the heart failure.
