Electrical features of focal activations
Among points with focal activations, approximately two-thirds showed
normal bipolar voltage, which is in line with a previous study by
Honarbakhsh et al. where almost half of focal activations occurred in
the areas of normal bipolar voltage.9 Although the
voltage of the DFAs was lower than that of the non-DFAs, the voltage in
DFAs was also frequently within the normal voltage range. Focal
activation may be less relevant in the LVA. Moreover, the majority of
bipolar electrogram morphologies at the points of focal activation were
categorized as a discrete type, whereas the fractionated type was rarely
found. The majority of discrete types were composed of single potential
components. These findings imply that focal activation is located in the
normal myocardium with preserved electrical voltage. Furthermore, the
nature of focal activation may be different from that of CFAE, which is
supported by the absence of a short CL in the focal activation. In this
regard, the different locations of the focal activations surrounded by
the CFAE area in the CARTOFINDER and ICL maps could additionally support
the above-mentioned hypothesis.
Focal activations had relatively short CLSD, and short CLSD was
associated with increased focal intensity, suggesting that focal
activities may consist of regular activities in temporal
characterization. Pappone et al. demonstrated that there were
repetitive-regular activities (RRas) during AF mapping, and that
ablation targeting RRas in combination with the other indicators
resulted in high rates of acute termination and long-term absence of
AF.16 Focal activations in our results share some
characteristics with the RRas: (1) RRas were defined as bipolar signals
with CLSD ≤ 30 ms, and 93.3% of focal activations in our study showed
CLSD ≤ 30 ms; and (2) both focal activities and RRas were often located
adjacent to the fragmented regions.
Previous works by Hansen et al. described a potential mechanism for
focal activation,5 demonstrating that the AF driver
was a micro re-entry based on pectinate muscle alignment in optical
mapping, and that this regular activity was transformed into
fibrillatory conduction. Since the electrical features of the focal
activations in our study were consistent with the abovementioned
hypothesis, the focal activations may correspond to the exit of the
micro re-entry circuit. In contrast, CFAE, which is often surrounded by
focal activations, may reveal slow conduction of the circuit. The
combination type of bipolar morphology may represent electrograms at the
border zone between the focal activation and CFAE areas.