parasystole

A second automatic rhythm existing simultaneously with normal sinus or other dominant rhythm, the parasystolic center being protected from the dominant rhythm's impulses so that its basic rhythm is undisturbed, although it may be manifest in the ECG only at various multiples of its basic periodicity. SYN: parasystolic beat. [para- + G. systole, a contracting]

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para·sys·to·le -'sis-tə-(.)lē n an irregularity in cardiac rhythm caused by an ectopic pacemaker in addition to the normal one

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para·sys·to·le (par″ə-sisґtə-le) [para- + systole] a cardiac irregularity attributed to the interaction of two foci that independently initiate cardiac impulses at different rates; as a rule, one of these foci is the sinoatrial node (the normal pacemaker), and the ectopic focus is usually in the ventricle. Each focus, and thus each rhythm, is protected from the influence of the other.