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Hopkins Pulse - Finding the Rhythm When Defibrillators Miss a Beat
Finding the Rhythm When Defibrillators Miss a Beat
Date: June 23, 2014
Johns Hopkins Resynchronization Optimization Clinic helps those who don't respond to cardiac resynchronization therapy.
Each beat of a healthy heart sends blood to the lungs to be refreshed and then recirculated throughout the body. Heart failure—a decline in the heart’s ability to constantly pump blood—can leave people feeling tired and short of breath, like North Carolina resident Susan Brinkley.
Brinkley’s heart failure comes in the form of cardiomyopathy, or the weakening or hardening of the heart muscle, which can be caused by everything from age to high blood pressure. It also occurs as atrial fibrillation, a rapid quivering of the heart’s upper chambers caused by a malfunction in the heart’s natural electrical system.
Normally, the heart delivers a charge to the upper right chamber, or atrium, which spreads to the walls of the lower chambers, or ventricles. The pulse causes the ventricles to contract near-simultaneously to pump blood up and out of the ventricles and into the lungs and body. In people with atrial fibrillation, the electrical impulses come from all over the upper chambers. Blood collects in the atria and does not completely fill the lower chambers.
To regulate Brinkley’s heart rhythm, surgeons implanted a biventricular defibrillator in her chest. When the defibrillator detects a rapid heartbeat, it sends a signal through the wires surgically placed in the right atrium and in both ventricles to restore a normal rhythm and cause the ventricles to contract within milliseconds of one another.
Although Brinkley was hoping that the device would restore her energy level so she could participate in activities with her children and grandchildren, as the months went by, she says, “I continued to be exhausted, and I wasn’t feeling any better.”
Her daughter suggested she visit the Johns Hopkins Resynchronization Optimization Clinic, which evaluates people who don’t seem to respond to cardiac resynchronization therapy (CRT).
According to cardiac electrophysiologist and clinic director John Rickard, only six or seven out of every 10 patients respond to CRT. “For the others, the prognosis for survival is very poor unless something is done,” he says.
The remedy, says Rickard, can be as simple as adjusting the device, modifying medications or getting other health conditions under control. At other times, a surgical procedure may be necessary to move or add an electrical lead.
After assessing Brinkley’s defibrillator, Rickard found that the wire to her left ventricle was not delivering enough energy to that side of her heart. “It was pacing the right ventricle all of the time, which can make the heart failure worse,” he says.
Rickard corrected the problem by increasing the voltage on the left lead. He also adjusted the timing on the device to mimic the natural pace of the heart, programming it to have a 20-millisecond (one-fiftieth of a second) head start before the firing of the right lead.
Now, Brinkley says she can breathe much easier. “I’m so grateful,” she says. “They took the time to figure out the problem.”