A rat model of complete atrioventricular block recapitulates clinical indices of bradycardia and provides a platform to test disease-modifying therapies

Figures

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  Figure 1. Design of electrosurgical needle ablation of the AV node. (A) An acupuncture needle and an ECG needle electrode, placed together to form a single unit to deliver electrosurgical energy and to record electrogram at the needle entry site. (B) The ablation needle and an ECG needle was assembled together with a polytetrafluoroethylene tape which also provides electrical insulation. The sharp end of the needle was bent at 3–4 mm from the end to limit the needle entry. (C) Illustration of the ablation needle, electrosurgical pen contact site, and the ECG electrodes during CAVB procedure. The intracardiac electrogram is recorded from the needle entry site (orange colored negative electrode) to left leg (orange colored positive electrode). (D) Needle entry is made through the anatomical landmark, fat pad, pointing toward the LV apex. (E) A photograph of the fat pad near the aortic root upon retracting the right atrial appendage.

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  Figure 2. Surface and epicardial electrocardiograms before and after CAVB creation. (A) An example of surface ECG and simultaneous recording of epicardial electrogram under normal sinus rhythm. (B) Typical transient ventricular arrhythmias that could be observed during needle entry into the AVN region. (C) Upon the needle entry into the proper AVN region, sharp depolarizations starting within the P-wave from the epicardial electrode can be observed from the subepicardial electrogram. Upon successful CAVB, the His-like potentials are no longer observed. (D) Long-term follow-up of the CAVB animals demonstrate stable and complete heart block for at least 4 weeks.

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  Figure 3. Extensive fibrosis in the AV nodal region 4 weeks after CAVB creation in 6-month old female rats. Masson’s Trichrome staining of the AVN area showing an increased presence of fibrotic tissue, (B to E, solid line) following CAVB surgery in four 6-months old female rats. The ablation site reveals extensive fibrosis compare with the normal rat heart (A, solid line) at 4-weeks post-CAVB creation procedure. The rats were 6-month old at the time of ablation and exhibited stable CAVB for 4-weeks post-surgery. (A) Histologic finding of healthy 6-months old female rat’s AV nodal area. (B–E) Representative histology 4-weeks post-ablation from 4 separate rats. The mean area of fibrotic region was 0.98 ± 0.15 mm2. MV, mitral valve; TV, tricuspid valve; IVS, interventricular septum.

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  Figure 4. The 3-month old rats’ poor survival upon CAVB correlates with their relatively smaller compact AV nodal region. (A) Event-free survival curve of the CAVB rats illustrates the poor survival rates of the 3-month old rats and 6-month old male rats. (B) Representative images from the normal AVN region (solid line) of male and female rats at 3-month or 6-month of age. Compact nodal region adjacent to the central fibrous body is demarcated with a black line in an inset on the left of the arrow. (C) Mean area of the AV nodal region was similar between males and females within the same age group, but was significantly larger in 6-month old animals compared to 3-month old rats. CF, central fibrous body; IAS, interatrial septum; IVS, interventricular septum; MV, mitral valve; TV, tricuspid valve.

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  Figure 5. Echocardiographic findings before and after CAVB creation. (A) A parasternal short axis view (top) and M-mode (bottom) of normal sinus rhythm rat prior to CAVB surgery. (B) A parasternal short axis view (top) and M-mode (bottom) of the same rat at one month after CAVB surgery. At one month after CAVB, the left ventricle exhibited severe enlargement compared to the baseline. Mean data from 6 rats are analyzed to compare hemodynamic functions before and one month after CAVB: systolic and diastolic interventricular septum (C), LV posterior wall thickness (D), LV internal diameter (E), LV end systolic volume and end diastolic volume (F), LV stroke volume (G), LV ejection fraction and LV fractional shortening (H), LV mass (I). ECG telemetry revealed incidences of spontaneous, non-sustained ventricular tachycardia (J) as well as frequent PVCs (K) during first few days after CAVB surgery. (L) Representative ECG finding after CAVB creation in 3-month old rats. Following AVN ablation, severe ventricular bradycardia was observed (top), followed by non-sustained ventricular tachyarrhythmia (middle), and eventually sudden cardiac arrest (bottom). (M) Ventricular arrhythmia inducibility of…

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  Figure 6. Focal TBX18 gene transfer to the left ventricular apex of CAVB rats creates ventricular pacing that is faster than the slow junctional rate. (A) Timeline of the study indicating creation of CAVB and confirmation of chronic and stable CAVB for 7 days, second thoracotomy and focal injection of Adeno-TBX18 at the left ventricular apex, and a 14-day recording of ECG telemetry. (B) Mean heart rates over 2 weeks of TBX18- or GFP-injected animals. Shaded areas indicate the standard deviation of the heart rate at each time point. (C) Surface ECGs from GFP- (top) or TBX18-injected rat (middle) obtained at the time of and 2 weeks after gene delivery. TBX18-injected animals often exhibited two competing ventricular rhythms, one presumably from the slow junctional rhythm (arrowhead) and the other due to TBX18-injection (arrows). (D) Heart rate histograms of TBX18-injected animals show that a second major peak emerges 7 days post gene delivery, which is faster than the slow junctional rhythm. (E) Cardiac axis mapping of GFP-injected (left) and TBX18-injected (right) rats at 7 days post-injection. The faster ventricular rhythm in TBX18-injected animals exhibits QRS axis change and wider QRS…