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- ED 4 | ED 5 | ED 6 | ED 7 | ED 8 | ED 9 |
Edition 6 (May / Jun 2007)
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ECG of a patient who has an implanted device for treatment of heart failure What’s the diagnosis?
The ecg shows bursts of multiple of impulses from a device called a cardiomyostimulator which is a specialised pacemaker manufactured by medtronic used in a procedure called a 'cardiomyoplasty'(description below) for the treatment of heart failure. The timing of the bursts can be altered but generally stimulus is provided every other cardiac cycle. This procedure was pioneered before the advent of cardiac resynchronisation therapy and there are patients worldwide who after 10 years since their original procedure continue to lead normal lives.
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| What is cardiomyoplasty? Cardiomyoplasty is a surgical procedure designed to expand the diseased or injured heart's capacity to pump blood. There are actually two operations in-volved in cardiomyoplasty, which is also called the muscle-flap procedure. In the first, physicians detach the latissimus dorsi, the large skeletal muscle in the back. The muscle is then allowed to "rest" for a week to 10 days to improve its blood supply. The patient will be hospitalized for several days, then discharged until the second surgery. During the second surgery, the muscle is wrapped around the heart like a blanket. Then, a special pacemaker is implanted into the abdominal area and connected to the heart and back muscle. This pacemaker "trains" the skeletal muscle to beat like the heart. |
| Who is a candidate for cardiomyoplasty? Candidates for this operation include those who suffer from chronic low cardiac output or irreversible con-gestive heart failure caused by disease or congenital defect. The patient cannot have undergone previous heart surgery. There are two types of muscle fibers: fast, or type II, and slow, or type I. Type I fibers, like those in the heart, allow sustained action without muscular fatigue. The type II fibers found in the skeletal muscle allow it to perform faster activities of limited duration. When the pacemaker is implanted during cardio-myoplasty, one of its leads is anchored to the outside of the heart; it senses the heart's natural electrical activity and carries this information to the pacemaker. The lead transmits this information to a muscle-pacing channel, which directs these impulses to a second lead, a system of insulated wires. Woven into the skeletal muscle, these wires conduct impulses to it, forcing it to contract and "squeeze" the heart. For approximately six weeks, physicians stimulate the skeletal muscle by increasing the impulse voltage for longer periods of time. This continues until the muscle fibers complete the chemical transformation necessary to regularly beat like the heart without tiring. |
| How is the pacemaker different from those used in conventional treatment? Conventional pacemakers deliver a single pulse to trigger contraction of heart-muscle cells. The sophisticated pacemaker used in cardiomyoplasty, called a cardiomyostimulator, sends multiple, precisely timed and controlled bursts of impulses to stimulate contraction of the muscle fibers. It creates a beat more like that of the heart. |
Submitted by Mr Stuart Allen, Consulting Editor. |
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