Electromechanical Mapping to Evaluate Heart Muscle

Overview

Patients with narrowed heart arteries who undergo coronary angiography (imaging of the heart's blood vessels) may participate in this "heart mapping" study designed to gain information about the condition of different areas of the heart muscle. In coronary angiography, a thin tube called a catheter is inserted through a small incision in the groin and pushed up to the heart. There, a contrast dye is injected, revealing areas of blockage in the coronary arteries-the vessels that supply blood to the heart muscle. As soon as the angiography is completed, patients in this study will undergo another procedure called "Biosense mapping." For this procedure, a special catheter with a tiny sensor at the tip will be inserted into the sheath that was used for the angiography and advanced to the heart's main pumping chamber-the left ventricle. The sensor detects the pattern of an electromagnetic field generated from a pad under the patient, and an image of the precise location of the catheter in 3-dimensional space can be seen on a computer screen. The catheter is then navigated to various precise locations in the ventricle, producing an electromechanical map that distinguishes scarred muscle tissue from healthy tissue-information that can be important in guiding treatment. When this mapping is completed, the patient will be given a drug called dobutamine to increase the heartbeat, and the mapping will be repeated. The heart may also be mapped while the heart rate is increased with a pacing catheter to simulate exercise. The test will be stopped if adverse side effects develop. Patients in the study will also have magnetic resonance imaging (MRI) and PET (positron emission tomography) scans to get additional information about the heart muscle, such as blood flow and metabolism rate.

A novel left ventricular (LV) mapping system (Biosense, Inc.) uses low-intensity magnetic field energy to determine the location of sensor-tipped catheter electrodes within the LV. On the basis of previous experimental and human studies correlating the extent of myocardial ischemia with the amplitude of electrical signals, we hypothesize that such an integrated LV electromechanical mapping system could be used to distinguish healthy from ischemic or immobile myocardium on the basis of the extent of electromechanical endocardial signals. If this hypothesis is confirmed, the ability to detect on-line myocardial viability and ischemia in the catheterization laboratory may be feasible. The present study attempts to distinguish between ischemic, immobile, and normal myocardium by comparing LV electromechanical mapping data at rest and during pharmacologic stimulation, with imaging studies using MRI, PET, thallium and echo in patients with coronary artery disease.