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Figure 1 The principle of the method. (A) The right atrium is paced at one site and recordings are made from five other sites. The electrogram in response to an extrastimulus is processed to emphasize small potentials, and then (B) the delay of each fractionated potential is measured for every electrogram recorded during the pacing sequence. (C) The delay of each potential is plotted against the S1S2 interval to form five conduction curves that characterize myocardial conduction between the pacing and recording electrodes. Point I is the S1S2 interval at which delay starts to increase. Each site is paced in turn with recordings made from the remaining electrodes, and 30 conduction curves are obtained. (D) The mean increase in electrogram duration and S1S2 interval at which delay increases is plotted on a scattergram. CSO = coronary sinus ostium; HARA = high anterior right atrium; HPRA = high posterior right atrium; IVC = inferior vena cava; LARA = low anterior right atrium; LPRA = low posterior right atrium; RAP = right atrial appendage; SRA = septal right atrium; SVC = superior vena cava.
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