Two variants of concealed trigeminy.

Long rhythm strips were analyzed from three patients with frequent unifocal ventricular extrasystoles. The predominant rhythm in each patient was concealed trigeminy; i.w., the number of conducted sinus beats, S, between extrasystoles satisfied the equation S = 3n --1, where n is any positive integer. In one of these patients, about one-fourth of the values of S did not satisfy this equation; however, all such exceptional values of S satisfied the equation S = 3n. In the other two patients, very few of the exceptional values of S fit the equation S = 3n, but they did conform to the equation S = 3n --2. It is proposed that in all forms of concealed trigeminy, there is a characteristic 3:1 block in the re-entry loop that is responsible for the extrasystoles. Furthermore, it is postulated that immediately after each manifest extrasystole, the 3:1 block is converted transiently to a 4:1 or 2:1 block in the "3n" and "3n--2" variants, respectively. After the first penetration of the block site after a manifest extrasystole, if the re-entrant impulse is concealed, the 3:1 ratio is resumed in both variants until the next manifest extrasystole appears.