Electrophysiological classification of normal and pathological sinus node function.

The sympathetic and parasympathetic neurological cardiac effects were blocked with atropine and propranolol. The intrinsic heart rate (IHR) was determined and rapid atrial pacing (RAP) was carried out before and after administration of the drugs. The primary and secondary postpacing parameters were examined in both circumstances. Normal (n = 31) and pathological (n = 20) cases were differentiated on the basis of the IHR. In the secondary phase (PPC 2-10) after autonomic blockade returned to the basic frequency was of exponential character in the great majority of normal IHR cases. Anomalies may appear in both the primary and secondary phases. They are of different types: one of them concerns the recovery time; another electrophysiological anomaly occurs when there is no return to the predrive normal cycle length after pharmacological neurotomy. In the secondary phase there may appear sinoauricular blocks. They may depend on or appear independently of the effect of the vegetative nervous system. The new test allows a physiopathological classification of normal and pathological sinus node function.