May 12, 1999 DALLAS, May 11 -- Upgrading the 'search-and-destroy' treatment that removes the abnormal heart tissue responsible for irregular heart rhythms may permit more individuals to benefit from the procedure, according to a new study in today's Circulation: Journal of the American Heart Association.
The treatment, radiofrequency ablation, is needed because, in the majority of individuals, drugs are ineffective in controlling the serious irregular heart rhythms called atrial tachycardia. While not immediately dangerous to most patients, this abnormal rhythm imposes an extra burden on it that eventually may damage the heart and lead to congestive heart failure, a condition in which the heart is unable to pump enough blood to meet the body's demands. The only way to control the condition of these patients is to find the source of the abnormal beat in the heart and to destroy the culprit tissue by radiofrequency ablation.
"Because the electrode technique currently used for detecting abnormal heart rhythms is time-consuming and technically difficult, it is not suitable for all individuals with irregular heartbeats. Thus, many individuals who could be benefiting from the ablation therapy are not able to," says lead author Claus Schmitt, M.D., head cardiologist of the electrophysiology department at the Deutsches Herzzentrum München, in Munich, Germany. In the study, Schmitt and his colleagues tested a new 64-electrode 'basket' catheter that transmits signals in many directions simultaneously. The standard catheter has only about four to 10 electrodes for mapping the heart.
With the upgraded technique, physicians insert the multiple electrode-bearing catheter into a person's blood vessel and guide it into the heart to search for the tissue housing the abnormal rhythm. Once the abnormal heart tissue is detected, radiowaves heat and destroy the tissue.
"The multielectrode basket catheter adds a new dimension to mapping the electrical signals of the heart for better treatment of abnormal heart beats," says Schmitt.
In the study, the new catheter detected the tissue source of abnormal heartbeats in 31 patients with atrial tachycardia. After identifying the location of the abnormal tissue, the physicians treated 16 of the 31 patients by 'burning' their abnormal tissue. Fifteen of these patients were cured, and no treatment complications were seen in the 16 patients.
These cure rates are comparable to results reported from other studies, the authors report.
People with atrial tachycardia often experience periods of abnormally rapid heartbeats involving one or both of the heart's upper chambers called the right and left atria. Their heart rates may jump to two or more times their normal rates for periods lasting a few minutes to several days. Symptoms of atrial tachycardia may include heart palpitations, shortness of breath, dizziness or fainting spells. This condition is more dangerous for patients who already have serious heart disease, Schmitt says.
To pump blood efficiently, the heart's pacemaking tissues must send electrical signals to heart muscles, with the four chambers of the heart contracting in proper order. Atrial tachycardia is caused by the generation of electrical signals from abnormal heart tissue. The signals cause one or both atria to contract rapidly and out of synch with the heart's lower chambers called ventricles.
Radiofrequency ablation destroys only a small bit of tissue. The procedure causes little or no discomfort and is performed under mild sedation and local anesthesia. Its success rate is greater than 90 percent with a low risk of complications.
The multielectrode catheter used in this study provides, within only a few beats of the patient's heart, a three-dimensional map of electrical activity in the patient's atrium. This information allows the cardiologist to quickly pinpoint the source of the abnormal heart rhythm. Moreover, the new catheter, which encircles the heart chamber, does not have to be moved around to locate the source of the abnormal signal, Schmitt says.
In this study, the new device was used on patients with suspected right atrial tachycardia because the right atrium is the easiest heart chamber to access, Schmitt says. He and his colleagues expect it may ultimately prove effective in mapping other kinds of abnormal heart rhythms. For example, it could be used in patients with irregular heartbeat arising from the heart's ventricles, a location that is also difficult to map.
Co-authors of the study are: Bernhard Zrenner, M.D.; Michael Schneider, M.D.; Martin Karch, M.D.; Gjin Ndrepepa, M.D.; Isabel Deisenhofer, M.D.; Sonja Weyerbrock, M.D.; Jürgen Schreieck, M.D.; and Albert Schömig, M.D. NR 99-1038 (Circ/Schmitt)
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