Carvedilol Suppressed Cardiac Autonomic Nerve Activities and Paroxysmal Atrial Tachycardia

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Introduction: We hypothesized that carvedilol can effectively suppress autonomic nerve activity (ANA) and paroxysmal atrial tachycardia (PAT). Method: We implanted radiotransmitters to record stellate ganglion nerve activity (SGNA), vagal nerve activity (VNA) and superior left ganglionated plexi nerve activity (SLGPNA) in 7 ambulatory dogs. Integrated ANA (Int-NAs) and PAT (>200 bpm) were determined before, during and after carvedilol treatment (25 mg/d for 7 d). Results: Carvedilol reduced heart rate (108±10 bpm to 99±10 bpm, p<0.05), suppressed Int-NAs (SGNA by 24%, VNA by 25% and SLGPNA by 14%; p<0.05 vs. baseline) and significantly reduced both the incidence (from 8±6 to 3±3 episodes/d, p<0.05) and the total duration (from 68±64 to 16±21 sec/d, p<0.05) of PAT. However, in spite of continued suppression of Int-NAs, the PAT incidence and total duration both rebounded (both p<0.05) after carvedilol withdrawal to 5±6 episodes/d and 36±60 sec/d, respectively. Conclusion: Carvedilol treatment suppressed ANA and reduced the incidence and duration of PAT episodes, indicating that reduction of ANA outflow contributes to its antiarrhythmic effects. The PAT rebound after carvedilol withdrawal was not due to rebound of ANA, but most likely due to beta receptor upregulation.