Cardiac resynchronization therapy, or CRT, is a medical technology used to help some people with heart failure. In these patients, the lower chambers of the heart may not contract at the same time, so each beat pumps less blood than it should. A CRT device sends carefully timed electrical pulses to coordinate the ventricles and improve pumping efficiency.
This matters because better synchronization can reduce symptoms such as fatigue, shortness of breath, and poor exercise tolerance.
A CRT system usually includes a pulse generator placed under the skin and leads that carry signals to the heart. One lead often paces the right ventricle, while another reaches the left ventricle through a vein on the heart surface, allowing both sides to be paced in a coordinated pattern. The goal is to reduce the delay between ventricular contractions so the heart ejects blood more effectively.
CRT does not cure heart failure, but it can improve heart function and quality of life for selected patients.
Key Facts
- CRT stands for cardiac resynchronization therapy.
- CRT uses timed electrical pulses to coordinate contraction of the right and left ventricles.
- Heart rate can be calculated as HR = 60/T, where T is the time in seconds between beats.
- Cardiac output is CO = HR x SV, where HR is heart rate and SV is stroke volume.
- Ejection fraction is EF = SV/EDV x 100%, where EDV is end-diastolic volume.
- A typical CRT system includes a pulse generator, a right ventricular lead, a left ventricular lead, and often a right atrial lead.
Vocabulary
- Cardiac resynchronization therapy
- A treatment that uses an implanted device to pace the ventricles so they contract in a more coordinated way.
- Ventricle
- One of the two lower chambers of the heart that pump blood out to the lungs or the body.
- Pulse generator
- The implanted battery-powered part of a CRT system that produces electrical pacing signals.
- Lead
- A thin insulated wire that carries electrical signals between the CRT device and the heart tissue.
- Ejection fraction
- The percentage of blood in a ventricle that is pumped out during one heartbeat.
Common Mistakes to Avoid
- Thinking CRT makes the heart beat stronger by squeezing it directly is wrong because the device sends electrical signals that guide timing, while the heart muscle still performs the contraction.
- Confusing CRT with a standard pacemaker is wrong because standard pacing may control heart rate, while CRT specifically coordinates the timing of both ventricles.
- Assuming every heart failure patient benefits from CRT is wrong because CRT is usually used for selected patients with electrical conduction delay and reduced pumping function.
- Ignoring ventricular timing is wrong because two ventricles contracting out of sync can lower stroke volume even if the heart rate is normal.
Practice Questions
- 1 A patient has 0.80 s between heartbeats. Use HR = 60/T to find the heart rate in beats per minute.
- 2 Before CRT, a patient has HR = 75 beats/min and SV = 55 mL/beat. After CRT, SV increases to 68 mL/beat while HR stays the same. Calculate the cardiac output before and after CRT in L/min.
- 3 Explain why pacing both ventricles at carefully timed intervals can improve pumping efficiency in a heart where the ventricles contract out of sync.