The diagnostic significance of real sinus node automaticity depression in symptomatic sinus bradycardia

Atrial overdrive pacing was performed, before and after autonomic blockade, in 42 consecutive patients (32 males and 10 females, mean age 46 +/- 11 years) with symptomatic sinus bradycardia. Patients were divided into two groups: Group I, 23 patients (mean age 43 +/- 8 years) with normal intrinsic heart rate (IHR) and normal intrinsic corrected sinus node recovery time (intrinsic CSNRT < 425 ms) and Group II, 19 patients (mean age 49 +/- 13 years) with abnormal intrinsic sinus node automaticity identified after autonomic blockade by abnormal IHR and/or by abnormal intrinsic CSNRT (> 425 ms). In addition to sinus cycle length, IHR, maximal CSNRT and sinoatrial conduction time (SACT) the real sinus node automaticity depression (SAD) was also evaluated, calculated after autonomic blockade (intrinsic CSNRT-SACT). Not all patients with an abnormal IHR showed abnormally prolonged CSNRT and not all patients with normal IHR had normal CSNRT. Among Group I (normal IHR) in 19 patients the real SAD was < 300 ms, while among Group II in 8 of 11 patients showing abnormal IHR the real SAD was > 300 ms. The abnormal value of SAD (> 300 ms) observed not only in patients with abnormal IHR and/or abnormally prolonged intrinsic CSNRT but also in several patients with normal IHR, increases the sensitivity of testing and may allow to detect even latent organic sinus node dysfunction. In conclusion, a synopsis of IHR, intrinsic CSNRT and intrinsic SACT with real SAD may be useful to estimate more accurately the degree of the impairment of intrinsic sinus node automaticity helping to differentiate the organic sinus node dysfunction from the autonomic one.