Correlation of impedance minute ventilation with measured minute ventilation in a rate responsive pacemaker

Although rate responsive pacing based on impedance minute ventilation (IMV) is now standard, there is almost no data confirming the relationship betwe en IMV from an implanted pacemaker and measured minute ventilation (V-E) du ring exercise. Nineteen completely paced adults implanted with Medtronic Ka ppa 400 pacemakers underwent symptom-limited maximal metabolic treadmill te sting using a modified Minnesota Pacemaker Response Protocol. Minute ventil ation (V-E, L/min) was simultaneously measured using the flowmeter of a res piratory metabolic gas analysis system and the transthoracic impedance minu te ventilation circuitry of the pacemaker. Correlation coefficients (r) wer e used to find the best fit line to describe the relationship between the t wo measurements. Mean (+/- SD) r values for the first, second, and third or der polynomial equations and for log and exponential equations were: 0.92 /- 0.08, 0.94 +/- 0.04, 0.95 +/- 0.04, 0.91 +/- 0.06, and 0.91 +/- 0.07, re spectively. None of the r values were statistically different from the firs t order equation. Transthoracic IMV as measured by the Medtronic Kappa 400 is closely correlated to measured minute ventilation and is represented wel l by a first order (linear) equation.