Features January 2013 Issue

Study: Cardiac Resynchronization Therapy Best to Treat Heart Block

CRT helps get both sides of the heart pumping blood more effectively.

Cardiac resynchronization therapy (CRT) provides significant benefit to heart failure patients with a condition known as “heart block,” according to a recent study presented at the American Heart Association Scientific Sessions in November 2012. Heart block occurs when the electrical activity throughout the heart is slowed or disrupted.

Traditionally, heart block has been treated with cardiac devices that send signals to the right ventricle only to help restore healthy electrical activity in the heart. In this study, called BLOCK HF, 342 patients were treated with that approach, while 349 patients were treated with biventricular pacing, which resynchronizes both sides of the heart. Those who underwent biventricular pacing had a 26 percent reduction in the combined endpoints of mortality, heart failure-related urgent care and deterioration in heart function as detected by echocardiography.

“This study affirmed our belief that biventricular pacing was important in patients with complete heart block,” says Bruce Wilkoff, MD, Director of Cardiac Pacing and Tachyarrhythmia Devices at Cleveland Clinic. “The study had a long period of follow-up which showed us that this impact continued for at least six years and likely longer. Often we think logically something should work a certain way but when we actually measure the response it isn’t true. In this case, we were on the right track in our thinking and are justified in using biventricular pacing in patients with complete heart block.”

Marty Bee

When a heart’s electrical activity is erratic or disrupted (above) CRT can help bring both sides of the heart back into a healthy rhythm

Electrical activity in the heart
When the heart is functioning normally, rapid electrical signals travel from the upper chambers (atria) to the lower chambers (ventricles), over and over again. The signals keep the heart beating in a synchronized rhythm and at a certain rate. A disruption of this electrical activity can lead to an abnormal heart rhythm, known as an arrhythmia.

Heart block is a type of arrhythmia and is categorized as first-degree, second-degree, or third-degree. First-degree heart block may be so mild that you don’t even know you have it, though some symptoms may be noticeable. Second-degree heart block may make you feel as though your heart is skipping a beat. It can also be serious enough to make you feel dizzy or faint. Third-degree heart block limits the heart’s ability to pump blood throughout the body, and can also cause fatigue and fainting. Third-degree heart block requires treatment, because it can also be fatal.

Pacing the heart
Dr. Wilkoff says that about half of all pacemakers are implanted to treat heart block, and that heart failure (HF) is often the cause of heart block. But research has shown that pacing the ventricles of HF patients who also have heart block could actually increase the risk of mortality and heart failure hospitalizations, he adds.

But as this more recent study shows, biventricular pacing with a CRT device appears to be a safer and more effective solution for HF patients with heart block.

“Heart failure is very common, and the treatment when a heart failure patient also has partial heart block (called a bundle branch block) has been shown to be improved for both symptoms and survival by biventricular pacing,” Dr. Wilkoff says. “This is in addition to the usual heart failure therapy of beta blockers, ACE (angiotensin-converting enzyme) inhibitors and diuretic medications. There was little information about using biventricular pacing in patients with complete heart block and this study looked at all patients, either with or without heart failure, comparing biventricular vs. single-ventricular pacing.”

He further explains that pacing only one side of a heart that has this kind of electrical complication doesn’t do enough to help the heart get back in a healthy rhythm.

“The ‘wires’ in a patient’s normal heart sends the electrical message to contract to the entire heart very quickly,” Dr. Wilkoff says. “With a bundle branch block or in the situation of right ventricular pacing the message only gets to one side of the heart and slowly gets to the other side. Therefore the heart is unable to pump the blood as effectively. Pacing both the right and left ventricles gets the message quickly to both sides of the heart and improves the pumping of the heart muscle in most patients.”

Researchers noted that implanting a CRT device is more complicated than a standard pacemaker, so physicians have been reluctant to put patients through that unless there was a clear benefit. Dr. Wilkoff says this study could have a significant impact on the treatment of patients with heart block in the months and years ahead.