CRT stands for cardiac resynchronization therapy, a device-based treatment for heart failure. A small device implanted in the chest sends precisely timed electrical signals to both lower chambers of the heart, forcing them to contract together instead of out of sync. This restores a more efficient pumping pattern, improves blood flow, and reduces heart failure symptoms in most people who receive it.
How CRT Works
In a healthy heart, the two lower chambers (ventricles) squeeze in unison. In some forms of heart failure, electrical signals travel through the heart muscle unevenly, causing the left and right ventricles to contract at slightly different times. That mistiming, even by fractions of a second, reduces how much blood the heart pushes out with each beat. Over months and years, the heart works harder for less output, and symptoms like fatigue, shortness of breath, and fluid buildup get worse.
A CRT device corrects this by delivering electrical impulses to both ventricles simultaneously through thin wires called leads. One lead is placed in the right ventricle, another is threaded through a vein on the surface of the left ventricle, and a third sits in the upper right chamber to coordinate timing with the heart’s natural rhythm. The result is a synchronized contraction that improves how efficiently the heart ejects blood and reduces the strain on the muscle.
CRT-P vs. CRT-D
There are two types of CRT devices. A CRT-P is a pacemaker-only device that synchronizes the ventricles but does nothing else. A CRT-D combines that same pacing function with a built-in defibrillator, which can detect and correct dangerous heart rhythms by delivering a shock.
In practice, most people who qualify for CRT also meet the criteria for a defibrillator, since the same degree of reduced heart function that warrants CRT also raises the risk of life-threatening arrhythmias. About 4% of CRT patients develop a device-related fast heart rhythm shortly after implantation, which a CRT-D can treat automatically. For this reason, CRT-D is generally preferred, though the decision depends on a person’s overall health, age, and individual risk profile.
Who Qualifies for CRT
CRT is not for all heart failure patients. Guidelines from the European Society of Cardiology and the American College of Cardiology define candidacy based on three main criteria: how weakly the heart pumps, how slowly electrical signals travel, and the pattern of that delay.
- Ejection fraction of 35% or lower. A normal heart pumps out roughly 55% to 70% of its blood with each beat. CRT candidates have significantly reduced pumping ability.
- Wide QRS complex on an ECG. The QRS measurement reflects how long it takes electrical signals to travel through the ventricles. A duration of 150 milliseconds or more with a specific delay pattern called left bundle branch block is the strongest indication. Patients with a QRS between 130 and 149 ms may also be considered.
- Persistent symptoms despite medication. Candidates are typically already on standard heart failure drugs but still experience breathlessness, fatigue, or exercise limitations.
People with atrial fibrillation can also qualify if their QRS is 130 ms or wider and there is a reliable plan to ensure the device captures both ventricles consistently, which can be more challenging with an irregular heart rhythm.
What the Procedure Looks Like
CRT implantation takes several hours and is performed under local anesthesia with sedation. A surgeon makes a small incision below the collarbone, threads the leads through a vein into the heart, and positions them using real-time X-ray imaging. The pulse generator, roughly the size of a stopwatch, is placed in a small pocket created under the skin near the collarbone.
Most people stay in the hospital for a few hours to overnight. You can return to normal daily activities within a few days, though driving and heavy lifting are typically restricted for about a week. The device is programmed before you leave and fine-tuned at follow-up visits to optimize the timing of the electrical pulses for your specific heart.
How Effective CRT Is
For people who respond well, CRT can produce noticeable improvements in energy, breathing, and exercise tolerance within weeks to months. In clinical trials, CRT reduced the combined risk of death or hospitalization for heart failure by 22% compared to standard right-ventricle-only pacing. Many patients also see measurable improvement in their ejection fraction over time as the heart remodels and becomes more efficient.
That said, roughly 30% of CRT recipients are classified as non-responders, meaning they see little or no clinical benefit. The reasons vary. People whose electrical delay does not follow a left bundle branch block pattern tend to respond less reliably. Scar tissue from a previous heart attack can interfere if a lead happens to be placed over the scarred area, since damaged muscle cannot contract normally regardless of the electrical signal it receives. In some patients with atrial fibrillation, up to half of what registers as biventricular pacing is actually a fusion of the device’s signal with the heart’s own impulse, reducing the therapy’s effectiveness.
Careful patient selection and precise lead placement are the most important factors in avoiding non-response. Advanced imaging before the procedure, particularly cardiac MRI to map scar tissue, helps surgeons position the left ventricular lead in the most viable area of heart muscle.
Risks and Complications
CRT implantation is considered relatively safe. In real-world registries and insurance databases, the overall complication rate is about 5.6%. The most common issues are lead-related: the wires can shift out of position, fracture, or develop sensing problems over time. Lead complications occur in roughly 11% of patients across real-world studies, though many of these are manageable with reprogramming or a minor revision procedure.
Other potential complications include infection at the implant site, bruising or blood collection in the device pocket, and a small risk of puncturing the lung membrane during lead insertion (pneumothorax). Serious complications are uncommon, and the rates in everyday clinical practice tend to be lower than those reported in clinical trials, likely because trial protocols require more aggressive monitoring and reporting.
Living With a CRT Device
After implantation, you will have periodic checkups to verify the device is functioning properly and the battery has adequate charge. Many modern CRT devices transmit data wirelessly to your care team, reducing the number of in-person visits needed. Battery life varies but typically lasts 5 to 10 years before the generator needs replacement, a shorter procedure since the original leads can usually stay in place.
Day-to-day life with a CRT device is similar to living with any pacemaker. You will need to avoid strong magnetic fields and let medical staff know about the device before certain procedures like MRI (though many newer devices are MRI-compatible). Most household electronics, cell phones, and airport security systems do not interfere with the device. The goal of CRT is not just to extend life but to improve its quality, and for the roughly 70% of recipients who respond, it delivers on that goal meaningfully.