Incessant pacemaker Vario ® operation

The Vario function is a feature of certain pacemakers that allows noninvasive voltage threshold determinations. 1 After programming the Vario option, magnet application over the pulse generator results in 16 asynchronous impulses at a frequency of Wmin (new unit), followed by 15 asynchronous impulses at a frequency of 120/min., A stepwise decrease in amplitude occurs during these latter 15 cycles, followed by a final 0 volt output signal. The decrement in voltage per cycle is determined by the programmed amplitude as well as battery status. In a new unit, at a 5 volt output, the step differential is 0.32 volts. Initiation of the Vario test results from engagement of a reed switch by the test magnet. A case is described where failure of the reed switch to disengage after magnet removal led to continuous Vario cycling.