Cardiac Resynchronization Therapy (CRT)

Cardiac resynchronization therapy is a special device treatment used for patients with advanced heart failure whose left and right lower chambers work out of step. Its medical short form is CRT, which stands for “Cardiac Resynchronization Therapy.” The word “resynchronization” means bringing back into sync; this is exactly what the device is designed for: to bring the heart back into sync.

In a healthy heart, the right and left lower chambers contract at the same time. This synchronized contraction lets the heart work efficiently. In some heart failure patients, this synchrony is broken; while the right chamber contracts, the left chamber lags behind. As a result, the heart cannot pump blood fully with each beat; pumping power drops. The patient runs into shortness of breath, fatigue, swelling in the feet, and trouble doing exercise.

A CRT device sends electrical signals to the lower chambers at the same time, restoring this synchrony. So the heart starts working more efficiently. Pumping power rises over time, the patient’s symptoms ease, and quality of life improves clearly.

Is CRT different from a pacemaker?

This question matters because a CRT device looks like a pacemaker from the outside. But how they work is different.

In a standard pacemaker, there are usually one or two wires. These wires are placed in the right upper chamber and the right lower chamber. When the heart beats slowly, the device sends signals from these points and keeps the heart at a sufficient rate. So a standard pacemaker is a solution for the “slowness problem.”

In a CRT device, three wires are used. Two wires are placed on the right side as in a standard pacemaker; the third additional wire is placed to stimulate the left lower chamber to contract. Placing this extra wire is what really sets CRT apart. With this third wire, signals can be sent to the right and left chambers at the same time, and contraction is brought into sync.

So a standard pacemaker is a rate regulator; CRT is a synchrony regulator. Their jobs differ, and they are placed in different patients.

Who gets a CRT?

A CRT is not placed in every heart failure patient. For the device to be of use, certain conditions must come together.

The first is heart failure symptoms. Despite medication, the patient should still be having shortness of breath, fatigue, and trouble doing exercise. The second is a clear drop in pumping power. This is shown by an echocardiogram. An echocardiogram is a painless imaging test that uses sound waves to show the structure and pumping power of the heart. Patients whose pumping power is generally below 35% are considered for evaluation.

The third and most critical condition is a specific finding on the ECG. An ECG, also called an EKG, is a simple, painless test that turns the heart’s electrical activity into a recording. In patients suitable for CRT, a finding called “wide QRS” is seen on the ECG. This finding shows that the lower chambers of the heart are contracting out of sync. CRT brings clear benefit especially in a condition called left bundle branch block.

Standard medication should be continued for at least three to six months. During this time, medications are titrated to suitable doses. If symptoms still continue at the end of this period and other conditions are met, CRT comes into play.

There are also different approaches for some additional conditions like atrial fibrillation. The decision is always individual; out of two patients with the same pumping power, one may be a CRT candidate while the other may not.

How does the device work?

After the CRT device is placed in the body, it constantly sends synchronized signals to the lower chambers. The patient does not feel this process. The device works quietly in the background, but the heart’s efficiency changes clearly.

The device also tracks the heart’s own beats. While the patient walks, rests, or sleeps, the heart beats at different rates; the device follows these changes and adapts. So CRT is not a device that gives a fixed signal; it is a smart device that constantly evaluates the heart and works according to it.

The device’s programming is set up specifically for each patient. Adjustments are made within the first few weeks after placement. These settings are the ones that let the heart work most efficiently, and they are reviewed at follow-ups when needed.

CRT-P and CRT-D difference

CRT devices come in two different types. Knowing the difference is important so the patient can recognize their own device.

CRT-P only carries out the resynchronization function. The “P” stands for pacemaker. This device guides the lower chambers to contract in sync and, when needed, keeps the heart at a sufficient rate like a standard pacemaker. But this device does not have the ability to deliver shocks for dangerous rhythm disorders.

CRT-D includes the defibrillator function on top of resynchronization. The “D” stands for defibrillator. This device both keeps the heart in sync and acts with a shock when a dangerous rhythm disorder develops. So CRT-D is, in a sense, the combined form of CRT and ICD.

Which device is placed depends on the patient’s additional risk status. CRT-D is preferred in patients with a history of dangerous rhythm disorder or those at high risk. If this risk is low, CRT-P may be enough. The decision is also made by considering the patient’s age, accompanying conditions, and life expectancy.

How is the device placed?

The procedure is done in an operating room or electrophysiology laboratory. This laboratory is a space specially equipped for procedures on the heart’s electrical system. The patient is not put fully to sleep; the area below the collarbone is numbed. A mild sedative may also be given.

A small cut is made in the skin and a pocket is created where the device will sit. Two of the device’s wires are guided through a vein near the collarbone and into the right side of the heart, as in a standard pacemaker. The third wire is what really sets CRT apart. This wire is guided through a vein that runs at the back of the heart (the coronary sinus) to the surface of the left lower chamber. The anatomy of this vein differs in each patient; so placing the third wire is the most challenging part of the procedure.

Imaging is used while placing the wires. Once all wires are in the right places, the device is placed under the skin and the cut is closed. The procedure usually takes two to four hours; it is somewhat longer than a standard pacemaker placement.

Most patients stay in the hospital for one night and go home the next day. For the first few days, the arm on the side of the device should not be lifted above shoulder height. This keeps the wires from shifting.

How effective is CRT?

When placed in the right patient, the effect of CRT is clear. In most patients, shortness of breath eases, they can walk longer, and they have less trouble climbing stairs. Fatigue and weakness recede. Some patients describe themselves as “going back to who I was years ago.”

The benefit of the device is not only in symptoms. The heart itself also improves over time. Pumping power rises; in some patients, it improves clearly. Hospital admissions drop and life expectancy lengthens.

But not every patient sees the same level of benefit. About three out of every ten patients do not get the expected benefit. These patients are called “CRT non-responders.” The reason can be related to wire placement, the structure of the disease, or scar tissue in the heart muscle. In cases of non-response, the programming is reviewed, and sometimes the wire position is changed.

The first benefits are usually noticed a few weeks after placement. The rise in pumping power becomes clear in three to six months. So the first evaluation is usually done after this period.

Battery life and check-ups

The battery inside the device lasts for years. The battery life of CRT devices is generally between six and ten years. Battery use is somewhat faster in CRT-D devices because they carry out both resynchronization and defibrillator functions. Delivering shocks costs the battery extra energy.

When the battery runs out, only the battery part of the device is replaced, not the whole device. The wires are already in place; only the pocket is reopened and the device is swapped. This second procedure is shorter than the first placement.

Regular check-ups are needed to make sure the device is working as it should. Check-ups are usually done every three to six months. During these check-ups, a special device reads the CRT’s battery, wires, heart rhythm records, and the signals delivered. Programming is adjusted as needed at these visits.

Many newer devices have remote monitoring. The patient is given a receiver; this receiver is kept in the bedroom and regularly sends device data to the doctor. So if a problem comes up between check-ups, it is noticed quickly.

Living with the device

After getting a CRT, most patients feel a clear rise in quality of life. Mild tenderness and some swelling at the site are normal in the first few weeks. Once the skin heals, the device feels like a small bump under the skin from the outside.

Mobile phones are safe to use; just avoid carrying the phone in the chest pocket on the same side as the device. During calls, holding the phone to the opposite ear instead of close to the device is the right way.

Microwaves, televisions, computers, hair dryers, and other household appliances do not cause problems. Airport security gates can be passed through, but the staff should be told about the device, and a hand search is preferred.

The situation around MRI varies by device. Most newer CRT devices are MRI-compatible. Before the scan, the brand and model of the device should be shared, and both the MRI center and the cardiology team should be informed. The situation is different for older devices.

Industrial environments with strong magnetic fields, electrocautery (the electrical cutting tool used in some surgeries), some physical therapy methods, and TENS devices used for pain relief may not be compatible with CRT. Always tell about your device before any medical procedure.

There is one extra thing patients with a CRT-D should know: if the device detects a dangerous rhythm disorder, it delivers a shock. What to do in this case is explained in detail in the ICD article.

Sports and physical activity

Most patients who get a CRT can start light to moderate exercise. Walking, swimming, and cycling are safe and usually advised; because regular exercise supports pumping power in heart failure patients.

Sports that involve lifting weights with the arm on the device side and that strain the chest area (such as bodybuilding) are not advised because they can damage the wires. Sports where there is a chance of taking a direct hit to the chest, such as boxing and martial arts, are also not suitable.

What kind and intensity of exercise is suitable is decided by the doctor. Many centers have heart failure rehabilitation programs; these programs let the patient start safe exercise under supervision.

Do medications continue?

Yes. A CRT device does not replace heart failure medications; it works together with them. The mainstay medications of heart failure treatment, such as beta blockers, drugs acting on the angiotensin pathway, mineralocorticoid receptor blockers, and SGLT2 inhibitors, continue after the device is placed.

In fact, as the patient’s condition improves with the effect of CRT, medications become better tolerated. Doses that could not be reached before may now be reached. This brings additional benefit.

Stopping or changing medications on your own is not the right path. The doctor evaluates and adjusts the doses at follow-up visits as needed.