ABNORMAL AUTOMATICITY AS MECHANISM OF ATRIAL TACHYCARDIA IN THE HUMANHEART - ELECTROPHYSIOLOGIC AND HISTOLOGIC CORRELATION - A CASE-REPORT

Abnormal Automaticity in Human Atrium. Introduction: A 32-year-old wom an was operated upon because of drug refractory atrial tachycardia. Me thods and Results: Electrophysiologic study was performed prior to ope ration. During surgery, epicardial mapping of the electrical activity of the left atrium was performed. The left atrial appendage was resect ed and studied in a tissue bath. Thereafter, histologic examination wa s 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 appendag e. 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 blo ck prevented spread of activation from the spontaneously firing cells to surrounding tissue. Histology showed that spontaneous activity aros e in an area with abnormal cells-characterized by an amorphous, pale e osinophilic staining cytoplasm and absence of nuclei-surrounded by nor mal myocytes. Conclusion: The observations indicate that the mechanism of the atrial tachycardia was based on abnormal automaticity in an ar ea consisting of a conglomeration of normal and abnormal myocytes.