Indications for electrophysiologic testing in the diagnosis and assessment of sinus node dysfunction.

CLINICALLY, sinus node dysfunction (SND) is a multifaceted disorder comprising not only disturbances of sinus impulse generation and conduction to the atria but also impaired impulse transmission within the atria and specialized cardiac conduction system, abnormalities of subsidiary pacemaker function, and increased susceptibility to development of paroxysmal or chronic primary atrial tachycardias. ` In recent years a variety of electrophysiologic testing procedures have been developed in hope of improving our ability to recognize when SND may be responsible for symptoms in patients. The rationale and method underlying electrophysiologic tests of "sinus node function" have been detailed previously (for example, refs. 3 to 8). The objective of this discussion is to provide an overview of indications for proceeding with electrophysiologic testing for SND and to highlight limitations that should be considered in using and interpreting test results. In this context, the term SND will be used to refer primarily to disturbances of sinus node impulse generation and sinoatrial conduction. Uses of electrophysiologic testing in SND. Electrophysiologic disturbances characteristic of SND may be caused by a wide array of processes that alter the anatomy of the sinus node and/or surrounding atrium, interrupt their functional integrity, and result in what may be termed primary or "intrinsic" SND. Alternatively, SND may be secondary ("'extrinsic") to disturbances of autonomic neural control8'9 or the effects of cardioactive drugs.?' The extent to which intrinsic and extrinsic SND overlap or coexist has not been well defined. However, it may be reasonable to assume that the presence of the former may increase susceptibility to extrinsic neural or drug effects. Electrophysiologic testing techniques have been developed with the objective of assessing both the princi-