Dual Chamber Pacing Pacing Modes

Abstract

The availability of tined or screw in leads is now making possible reliable long term atrial pacing and/or sensing. Progress in circuits and battery design lead to a reappraisal of dual chamber (DC) pacing. 3 methods are commonly used: VAT pacing: is the oldest method designed in 1963. The absence of ventricular sensing is the major disadvantage of VAT pacing with, as a consequence, possible ventricular vulnerable zone stimulation and VOO pacing in case of atrial sensing failures. The low cost and long refractory period of VAT pacemakers resulting in an extremely low risk of Electronic Reentry Tachycardias (ERT) are however advantages which maintain the existence of this obsolete mode of DC pacing. VDD pacing combines the theoretical advantages of V A T and VVI pacing. Like VAT, VDD pacing results in fixed rate ventricular pacing if the minimal ventricular pacing rate becomes superior to the sinus rate. A modified version of the VDD mode called RS (Rate Sensitive) aims to roughly adjust the ventricular rate to the sinus rate without providing true A-V synchrony. DVI pacing is offered in 2 versions: — non-committed: ventricular stimulation occurs only if no spontaneous QRS is present following atrial stimulation; — committed, when ventricular stimulation always follows atrial stimulation: the absence of atrial sensing results in possible atrial vulnerable zone stimulation — in the absence of spontaneous variation of the ventricular rate, a major limitation. DVI pacing is generally considered as the 2nd choice mode of DC pacing. DDD pacing is the most sophisticated mode of DC pacing, with the theoretical advantages of the previous DC pacing systems providing in all instances A-V synchrony.