Physiological principles of a new method for rate responsive pacing using the pre-ejection interval.

The pre-ejection interval (PEI) was measured in 30 patients during isotonic and isometric exercise, emotional stress, isoproterenol infusion, Valsalva maneuver, carotid massage, atropine injection and incremental pacing. In patients with complete AV block, the simultaneous atrial rate was used as a standard of comparison to assess the changes observed in PEI. The sensitivity, specificity, proportionality and speed of response were evaluated to determine the applicability of PEI for rate responsive pacing. PEI shortened promptly and proportionately to atrial cycle length with isotonic and isometric exercise, emotional stress, and isoproterenol (R values from 0.88 to 0.98, p less than 0.001). It was neither affected by preload changes (Valsalva) nor by parasympathetic system (carotid massage and atropine). Incremental pacing had no effect in most of the patients but some showed a slight prolongation, similarly to what is observed with atrial cycle length. It is concluded that PEI is suitable for rate control in physiologically adaptive pacemakers.