What Are Cardiac Resynchronization Therapy Devices?

Reviewed by: HU Medical Review Board | Last reviewed: November 2019

Cardiac Resynchronization Therapy (CRT) is sometimes recommended by your cardiologist when medications have been unable to relieve symptoms of heart failure (HF).1-2 When the left ventricle becomes weak and damaged, it dilates or stretches out. This causes it to beat out of sync with the right ventricle causing worsening symptoms. The ventricles contract and relax out of sync.1-2 This can be seen on an EKG or echocardiogram. CRT may be used to improve the symptoms of heart failure and prolong long-term survival.


CRT is also known as biventricular pacing. A traditional pacemaker stimulates the right ventricle of the heart. A CRT device has 3 wires (or leads) that are placed in the right atrium, right ventricle and adjacent to the left ventricle. The device is programmed to triggers the left ventricle and the right ventricle to contract simultaneously.1 The resynchronization device stimulates contractions of the left ventricle and paces the right ventricle so that they beat in unison.2

An implanted CRT is a small battery-powered pacemaker device designed to help the heart to beat in a regular rhythm.1-3 It is an effective tool in the management of heart failure. Because patients with systolic heart failure are at increased risk of sudden cardiac death, an ICD/CRT combination device can be implanted. It is also called a CRT-D or ICD/biventricular pacemaker. Some patients will receive an ICD first and as their heart failure progresses they may get upgraded to a CRT-D.

CRT insertion

A CRT is commonly inserted surgically through a small incision just below the collarbone. It is fitted into a pocket created between the skin and the chest muscle.1,3 The cardiologist guides the attached 3 wires to position them through the chest through a vein and into the heart.1,3 The procedure generally takes 3 or more hours under local anesthesia.1,3

Following the procedure, there may be some pain, bruising, or discomfort which should resolve quickly. There will be some restrictions on activities and/or exercise for about 5 weeks. In order to ensure that the leads do not move after implant, you cannot lift your arm above your shoulder and should avoid lifting anything heavy or perform activities that would place a strain on or near the surgical site. Your healthcare team will give you instructions on what you can expect to feel from CRT and any precautions to take so as not to experience disruptions in CRT function.1

How does the CRT work?

The CRT helps the heart to beat with the right rhythm. The pacemaker function restores the normal timing pattern of contractions.3 It coordinates the timing of the upper and lower chambers of the heart as well as between the left and right sides of the heart.

The CRT uses its generator to send electrical impulses to the heart. The attached wires placed in the right atrium and right ventricle and alongside the wall of the left ventricle send small electrical signals through the wire to the heart to help it pump effectively.3 With this type of pacemaker, your heart will be paced most of the time. The goal is 100% Biventricular pacing which can improve symptoms, improve the functioning of the heart (increase EF %) and help you live longer.

What you need to know

A CRT needs to be evaluated to see how well it is working. This can be done remotely through a monitor at your home that transmits a signal through your telephone line, through cellular service or through your wireless internet network. A periodic evaluation provides information on battery life, condition of the leads, and any abnormal rhythms that have occurred since the device was inserted.3 Always let your non-cardiac healthcare team know that you have a CRT. Some medical or dental procedures may require precautionary measures.1 You may even set off a metal detector. It may be recommended that you stay away from devices with strong magnetic fields.

You should carry a CRT ID card with you. It should include personal information including the type of device, manufacturer, make, model and serial number. It also lists the date of implantation and emergency contact information. These ID cards are available in different forms including ones that can be downloaded for free from the internet.3


Cardiac Monitoring Devices

There are other kinds of monitoring devices used to evaluate heart rhythms and/or symptoms in people who have heart failure.

A Holter monitor is an external monitoring device that monitors and records the activity of your heart. It is a portable battery-powered monitor that attaches to electrodes or a patch placed on your skin. It delivers no electrical signal. It is an ambulatory electrocardiogram which is a device able to provide continuous monitoring for 24 hours up to an entire month as you go through your daily activities. This monitoring allows your provider to evaluate your heart rhythm under a variety of circumstances.4 There are other types of external monitors that can be worn for various time periods to evaluate your heart for abnormal rhythms.

Implantable Loop Recorder

An implantable loop recorder is a small monitoring device that can monitor your heart rhythm for up to 3 years. It is placed just under the skin in the left upper chest and can remotely send data to your providers about your heart rhythm. It does not send any electrical impulses, it simply monitors and records your heart rhythm. It is used to watch for very slow or very fast heartbeats or abnormal rhythms.

CardioMEMS is a wireless heart failure (HF) monitor that can reduce hospitalizations and improve the quality of life for people living with heart failure. It is an implanted device that measures pulmonary artery pressure through a radio sensor that is transmitted back to a monitoring facility. It is placed through the right heart catheterization procedure into one of your pulmonary arteries. Once in place, it measures your pulmonary artery pressure which is a sensitive measurement of fluid status or congestion. It does not alter heart rhythm, however, it sends important clinical information to your healthcare team which can be used to direct your medical care.5

Optimizer Smart system delivers cardiac contractility modulation therapy. This means it helps the heart contract more regularly. It is used to treat people with chronic, moderate-to-severe heart failure who have failed with medication and are unable to use other heart failure devices, like CRT. It is indicated by the FDA to improve the distance that can be walked during a 6-minute period and the quality of daily life. It also improves the functional status of people who have experienced limitations doing physical activities and continue to have symptoms even after receiving medical treatment.6

The optimizer smart system consists of a pulse generator, battery charger, programmer and software. Like other devices, the generator is implanted under the skin in the upper area of the chest and connects to three wires that are implanted in the heart. The device delivers electrical impulses to the heart with each regular beat to improve the effectiveness of the squeezing function of the heart.7

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