Noninvasive Electroanatomic Mapping of Human Ventricular Arrhythmias with Electrocardiographic Imaging

Noninvasive imaging of cardiac electrical activity during ventricular arrhythmias enables superior diagnosis and treatment. A New View of the Beating Heart Just as a tree’s shadow is an oversimplification of branches and foliage, the electrocardiogram, a decades-old tool for measuring the electrical activity of the heart, captures only an approximate view of the heartbeat, distorted by the intervening tissues between the heart and the few electrodes on the skin. This poses a problem when trying to treat heart diseases such as dangerous ventricular arrhythmias, which destabilize the heartbeat and can lead to sudden cardiac death. Now, with a technique called electrocardiographic imaging (ECGI), Wang and colleagues have married multiple electrical recordings from the skin of patients who have ventricular tachycardia (VT) with detailed computerized axial tomography (CAT) scans of the anatomy of their torso. From these data, the authors can back calculate what is happening, electrically speaking, on the surface of the misbehaving hearts, yielding an individual portrait of that patient’s beating heart so that treatment can be more effectively deployed. Twenty-five patients with VT were scheduled to undergo electrical mapping of their hearts and then ablation of heart tissue to correct the electrical defect with an invasive catheter. The authors augmented this standard treatment by creating an image of their beating hearts with noninvasive ECGI, before the standard procedure. The ECGI and standard procedure identified the same origination point of the tachycardia in almost all of the patients, and ECGI was able to correctly categorize both focal and reentrant mechanisms of VT. The time resolution of ECGI enabled the authors to follow the response of the heart to different patterns of stimulation (or pacing), revealing presystolic activation near the site of origin. They could see variable beat-to-beat conduction patterns and showed that the abnormal conduction patterns often began in regions of scar tissue, relics of previous heart attacks. ECGI yields information comparable to the current procedure for mapping abnormal heart activity with a catheter-fed electrode, repeatedly placed on the heart surface. But it has significant advantages over the current approach: The spatial resolution of the ventricular arrhythmia on the heart surface is high, and it takes into account patient-to-patient variability in body size and shape. Further, it is noninvasive and can map single heartbeats, allowing unprecedented visualization of the anatomy of the electrical activation and beat-to-beat variability. These advantages should enable more effective diagnosis of VT and more appropriate drug or ablation therapy, which can now be directed to the specific characteristics of the patient’s heart instead of a simplified shadow. The rapid heartbeat of ventricular tachycardia (VT) can lead to sudden cardiac death and is a major health issue worldwide. Efforts to identify patients at risk, determine mechanisms of VT, and effectively prevent and treat VT through a mechanism-based approach would all be facilitated by continuous, noninvasive imaging of the arrhythmia over the entire heart. Here, we present noninvasive real-time images of human ventricular arrhythmias using electrocardiographic imaging (ECGI). Our results reveal diverse activation patterns, mechanisms, and sites of initiation of human VT. The spatial resolution of ECGI is superior to that of the routinely used 12-lead electrocardiogram, which provides only global information, and ECGI has distinct advantages over the currently used method of mapping with invasive catheter-applied electrodes. The spatial resolution of this method and its ability to image electrical activation sequences over the entire ventricular surfaces in a single heartbeat allowed us to determine VT initiation sites and continuation pathways, as well as VT relationships to ventricular substrates, including anatomical scars and abnormal electrophysiological substrate. Thus, ECGI can map the VT activation sequence and identify the location and depth of VT origin in individual patients, allowing personalized treatment of patients with ventricular arrhythmias.