Transesophageal Atrial Burst Pacing for Atrial Fibrillation Induction in Rats

The present protocol can be successfully used in rats with healthy or remodeled hearts in the presence of a wide variety of risk factors for acute or long-term follow up studies. This protocol allows studying atrial fibrillation in different pathophysiological conditions to evaluate novel prophylactic and therapeutic strategies. After anesthetizing an adult wistar rat, place the rat in a supine position on a heating pad to maintain its body temperature at 37 degrees Celsius.

Then, attach three surface ECG electrodes to the rat limbs in a lead II configuration by placing the negative electrode on the right forelimb, the positive electrode on the left hindlimb, and the grounding electrode on the left forelimb. Secure the electrodes into position using thin elastic bracelet string chords. Next, turn on the surface ECG recording and perform continuous ECG recording throughout the procedure using a commercial or a locally developed acquisition program.

For electrical stimulation, use a five or six French quadripolar catheter connected to a microcontroller-based cardiac pacemaker. Once the route is fully anesthetized, insert the catheter through the oral cavity into the esophagus. To confirm the correct position of the stimulation catheter at the level of the atria, apply electrical stimulation at a frequency of 400 stimuli per minute.

Then, check whether the ECG tracing shows constant capture of the atria. Based on this, determine the diastolic threshold defined as the lowest voltage required to obtain atrial capture. For rats in the stimulation group, once the correct position of the catheter is determined, set the stimulator to a frequency of 4, 000 stimuli per minute at a voltage of three volts above the diastolic threshold.

Then, for each rat, apply 15 successive cycles of stimulation, 20 seconds each, with a free interval of five minutes between cycles. Next, check the effectiveness of the stimulation by identifying the sinus node recovery time, which appears at the end of the rapid pacing as a time interval that is longer than the cycle length recorded during sinus rhythm and represents the interval of time required for resumption of sinus rhythm after overdrive suppression ends. Then, identify the occurrence of the atrial fibrillation episode defined as the presence of three or more consecutive, irregular, supraventricular beats with P-waves absent or replaced by small, distorted F-waves.

For rats in the sham group, after inserting the catheter through the oral cavity, maintain the catheter in position for 18 minutes without applying any electrical stimulation, while continuously recording the surface ECG. On the first day of stimulation, 80%of the rats that received electrical stimulation presented atrial fibrillation episodes Out of the applied 164 stimulation cycles, 42 were followed by atrial fibrillation episodes. During the 10 days of stimulation, on average, 15.6 atrial fibrillation episodes were efficiently induced in all animals.

Of the total stimulation cycles applied, 20%were followed by atrial fibrillation and 41 episodes lasted more than 600 seconds. For episodes lasting less than 600 seconds, the average duration was 40.12 seconds. The present technique is relatively easy to reproduce and no special training is required for laboratory personnel who regularly work with animal models.

Following this procedure, continuous ECG recording using a telemetry device can be performed to assess spontaneous atrial fibrillation episodes and heart rate variability.