The presence or absence of atrial potentials could
The presence or absence of atrial potentials could not be confirmed by the VEGM. Consequently, atrial potentials with atrial event markers could not be differentiated from FFRW or noise activity in the VEGM (Fig. 6). In addition, tiny suspected atrial potentials without any atrial event markers could not be differentiated from conditions with no atrial potentials or where masking of the atrial event markers occurred due to the PVAB bace inhibitors in the VEGM (Fig. 7). In this type 2 case, atrial potentials were intermittently overlaid on the PVAB period and even manual analysis could lead to a misdiagnosis of ventricular tachycardia (Fig. 7).
Discussion In type 1, although the atrial electrogram is visible in the SEGM, it can be masked by a large QRS wave or T wave. The atrial potentials in the PVAB period are particularly difficult to differentiate from FFRWs and the absence of electrical markers makes a complete analysis difficult (Fig. 1A). Conversely, the AEGM can clearly indicate the atrial electrogram without the need for atrial event markers because of the small effect of the QRS and T wave on the atrial electrogram. The ventricular potential is generally large and can be confirmed as an FFRW, which can then be clearly differentiated from the atrial potential (Fig. 1B). Since the VEGM is demonstrated with an auto-adjustment of sensitivity with reference to the ventricular potential, tiny atrial potentials are frequently obscured and confirmation of the atrial electrogram is dependent on the presence of atrial event markers. Therefore, possible under-sensing within the PVAB period and over-sensing due to FFRWs or electrical noise cannot be excluded (Fig. 6). In type 2, when an atrial potential is located just after a ventricular event, the atrial event marker is not reliable because of the PVAB period. Furthermore, in cases where an atrioventricular conduction delay is enhanced, the atrial and ventricular potentials can fuse, thus becoming very difficult to differentiate in the SEGM (Figs. 2A and 8A). Conversely, the AEGM can always demonstrate atrial potentials clearly, and the atrial potential can be confirmed without the need for atrial electrical markers, even if the atrial and ventricular potentials are fused. In addition, ventricular potentials can usually be confirmed as FFRWs by a manual evaluation in the AEGM. If ventricular potentials cannot be confirmed manually, the ventricular marker channel will still show the presence of ventricular potentials because the ventricular electrogram is not associated with the ventricular blanking period during atrial tachycardia (Figs. 2B and 8B). With VEGM selection, the atrial potential tends to be obscured and a misdiagnosis of VT can occur if atrial tachycardia is associated with a remarkable atrioventricular conduction delay and atrial potentials repeatedly coincide with the PVAB period (Fig 7–1). In type 3, the auto-gain control for the SEGM adjusts the amplitude of the ventricular potential, with the result that the atrial potentials become too small to be visible. When the atrial potential is located just before the ventricular potential, the 2 potentials fuse and it is difficult to differentiate the atrial potential from FFRWs; this is true even if atrial electrical markers exist (Fig. 3A). If the atrial potential is located just after the ventricular potential, it can be challenging to differentiate between the 2 potentials; in addition, no atrial electrical markers are available due to the PVAB. However, changing the intracardiac EGM from the SEGM to the AEGM highlights the atrial potential, and the ventricular potential can still be confirmed as an FFRW in most cases. More reliable confirmation of the atrial and ventricular potentials leads to the diagnosis of ventricular tachycardia (Fig. 3B). In type 4, the SEGM exhibits smaller atrial potential amplitude. When the atrial potential overlaps with the ventricular potential, the atrial potential is masked by the larger amplitude of the ventricular potential and differentiating between atrial potentials and artifacts becomes more difficult (Fig. 4A). Changing the EGM to the AEGM attenuates the ventricular potential, magnifying the atrial potentials so that atrial potentials can be differentiated from noise and FFRWs. Finally, a misdiagnosis of AHR due to over-sensing of electrical noise will result (Fig. 4B).