Increased susceptibility to ventricular arrhythmias in hypertensive paraplegic rats

Individuals with spinal cord injury (SCI) between thoracic vertebrae four (T4) and five (T5) have elevated levels of sympathetic activity to the heart. Notably, female spontaneously hypertensive rats (SHR) also have increased cardiac sympathetic nerve activity (SNA). Since elevated levels of cardiac SNA increase the risk for cardiac arrhythmias, we tested the hypothesis that hypertensive, paraplegic rats have an increased susceptibility to ventricular arrhythmias. To test this hypothesis, intact (n = 7) and paraplegic hypertensive rats (n = 6) were chronically instrumented with silver stimulating electrodes on the left ventricle, electrocardiogram (ECG) recording electrodes and an arterial catheter. After recovery, the effective refractory period, the electrical stimulation threshold to induce ventricular arrhythmias and cardiac sympathetic tonus (ST) were determined. Paraplegic rats had a lower effective refractory period (35%), lower electrical stimulation threshold to induce ventricular arrhythmias (62%), and higher cardiac ST (84%). These data document an increased susceptibility to ventricular arrhythmias in hypertensive, paraplegic rats.