Rapid Atrial Pacing Promotes Atrial Fibrillation Substrate in Unanesthetized Instrumented Rats

FIGURE 1. AF substrate analysis in unanesthetized rodents. (A) Schematic presentation of the experimental setup. MBHE was implanted on the RA for atrial pacing. One pole of the atrial electrode was also utilized to acquire high resolution recordings of the atrial signal (Atrial-Unipolar). (B) Photographs of an implanted rat and an implanted mouse freely moving in the EP cage during the RAP protocol. (C) Example of an AF episode triggered by burst pacing. This episode of 82 s was recorded from a rat that was exposed to RAP for 7 consecutive days (see Figure 2 for details). Left: Baseline ECG and atrial-unipolar recordings. Middle: Standard burst pacing protocol (20 s, 100 Hz, double threshold). Right: Post-burst recordings of an AF episode and its conversion to sinus rhythm. In each condition, 10 consecutive bursts were applied. AF substrate was evaluated in regard to the % of positive episodes (>1 s) and the total AF duration.

FIGURE 2. Increased AF substrate in rats exposed to RAP. (A) Analysis of AF induction. 3D plots of daily evaluation in five RAP rats (left) and six Sham rats (right). In both plots each color represents a different rat. For the RAP animals evaluation was continued until capture was lost or was too high to keep with the RAP. For the Shams, evaluation was maintained for 6–8 days. Note absence of AF induction in the majority of rats at baseline as well as following 1 day of RAP. Also note increased AF substrate following 2 days of RAP. (B) Analysis of Total AF duration. 3D representation as in (A) above. (C,D) Comparison of the AF substrate parameters before and after 2 days in the RAP vs. Sham rats. Note the strong tendency of increase in AF induction and AF duration following 2 days in the RAP group. Also note increased AF duration following 2 days in the RAP group vs. the Sham group.

FIGURE 3. Absence of AF substrate augmentation in mice exposed to RAP. (A,B) Analysis of AF induction and AF duration in seven mice in which RAP could be maintained for up to 7 consecutive days. 3D plots of daily AF evaluation as in Figure 2. Note that only one animal demonstrated AF episodes and no clear effect of the RAP could be detected. (C,D) Summary analysis comparing the AF substrate before and after 48 h of continuous RAP at CL = 50 ms. Note absence of AF substrate augmentation following RAP in mice.

FIGURE 4. Paradigm for evaluation of transcriptional effects of RAP on left atrial tissue of rats. (A,B) Schematic diagrams of microarray study design and basic outcome. (C,D) RT-qPCR for eight genes of interest indicating data reliability.

FIGURE 5. Analysis of four Micro RNAs known to be involved in AF-related remodeling. Note significant downregulation of MIR-101, and MIR-26A as well as a non-significant tendency of reduction in MIR-1. MIR-328 was unaffected by RAP (n = 3 for both RAP and control pacing, Mahan–Whitney test).