Electrophysiology study (EPS) tracing during mapping of atrial tachycardia

Shown are three surface electrocardiogram (ECG) leads (I, aVF, V1) and intracardiac recordings from the high posterior right atrium (HRA); posterior left atrium (USER1 and USER 3); proximal, mid, and distal coronary sinuses (CS9-10, CS5-6, CS1-2); and right ventricular apex (RVA). The patient had an incessant atrial tachycardia and dilated cardiomyopathy (left ventricular ejection fraction 9 percent) referred for cardiac transplant evaluation. The P wave (*) falls at the end of the T wave in the surface ECG; its onset is difficult to discern. However, the intracardiac electrograms demonstrate obvious atrial (A) and ventricular (V) activity. Activation mapping involves positioning the mapping catheters in the right (HRA) and left atria (USER) to record earliest electrical activity during the tachycardia. The left atrial catheter records earlier electrical activity (arrow) than the right atrial catheter, but the timing with respect to the surface P wave is obscured because of the T wave of the preceding QRS complex.