A right atrial or ventricular electrode may sense intrinsic electrical activity or provide electrical stimulation (pacing). Pacing in one chamber may occur at a fixed rate, i.e. independent of sensing in either chamber (and hence of intrinsic activity). Alternatively, demand pacing allows sensing to regulate the pacing function. An intrinsic rate (e.g. 70 beats/min) is set, with an associated R-R interval of 85Z ms. If a gap of more than 85Z ms is detected after the R-wave, i.e. the rate is below 70 beats/min, a pacing spike will be delivered.
The combinations of different chamber sensing and pacing interactions have been coded using five symbols. The first three describe the chamber(s) paced and those sensed (O, none; A, atrium; V, ventricle; D, atrium and ventricle), and the response to sensing (O, none; T, triggered; I, inhibited; D, triggered and inhibited). The fourth and fifth symbols describe programmability and antitachyarrhythmia functions respectively. Common modes encountered are shown in Table 1.
'(Oj rHti* wibli punluMI nnn^mi
HfiCfc P-_n 1 ■ ■ ^ MM Wi^fl riI Pt^uiHOMimJir4ft^ii«ilr«i^lmiv hik1 imu uim ruw li rf44n-ii in n jinn w«^ 1 nwf d rm («if ni*m.
gw "an n mv rw>t. Civ v wo At-uvwe/llAii i-uifl A nih«
Table 1 Common pacing modes
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