Abnormal Automaticity as Mechanism of Atrial Tachycardia in the Human Heart—Electrophysiologic and Histologic Correlation:

Abnormal Automaticity in Human Atrium, introduction: A 32‐year‐old woman was operated upon because of drug refractory atrial tachycardia. Methods and Results: Electrophysiologic study was performed prior to operation. During surgery, epicardial mapping of the electrical activity of the left atrium was performed. The left atrial appendage was resected and studied in a tissue bath. Thereafter, histologic examination was performed. Polarity of the P wave in the surface ECG suggested that the tachycardia originated high in the left atrium. Epicardial mapping disclosed earliest activation in the apex of the left atrial appendage. Intracellular recordings from surgical specimen made at the site of origin, which was marked during surgery, revealed cells with phase 4 depolarization at cycle lengths ranging from 360 to 540 msec. Exit block prevented spread of activation from the spontaneously firing cells to surrounding tissue. Histology showed that spontaneous activity arose in an area with abnormal cells‐characterized by an amorphous, pale eosinophilic staining cytoplasm and absence of nuclei‐surrounded by normal myocytes. Conclusion: The observations indicate that the mechanism of the atrial tachycardia was based on abnormal automaticity in an area consisting of a conglomeration of normal and abnormal myocytes.