What is the role of pharmacologic stimulation tests in the workup of sinus node dysfunction (SND)?

Updated: Nov 30, 2018
  • Author: Bharat K Kantharia, MD, FRCP, FAHA, FACC, FESC, FHRS; Chief Editor: Mikhael F El-Chami, MD  more...
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Answer

This section outlines steps to allow systematic evaluation of sinus node (SN) function.

Calculating the intrinsic heart rate (IHR)

The IHR is the heart rate in the presence of complete pharmacologic denervation of the SN. This is achieved with the simultaneous use of beta blockers and atropine. The calculation of the IHR following simultaneous administration of beta blockers and atropine is largely of historical interest and is rarely performed in the modern evaluation of patients with suspected SN dysfunction (SND). The IHR in a healthy person is approximately equal to 117.2 – (0.53 × age in years).

Sinus node response to pharmacologic challenge

A number of drugs have been used in to aid in the diagnosis of SND. The pharmacologic protocols are briefly described below.

Atropine and isoproterenol

Atropine (1 or 2 mg) and isoproterenol (2-3 mcg/minute) may be useful, because both agents normally increase the sinus rate. A suggested abnormal response is an increase in the sinus rate of less than 25% above the baseline, or to a sinus rate below 90 beats per minute. [31] Due to fact that in most cases the diagnosis of SND can be achieved by establishing a symptom-rhythm correlation with the use of ambulatory monitoring in conjunction with a comprehensive history and physical examination, testing with these agents is rarely necessary.

Adenosine

Adenosine has been proposed as an alternative to invasive electrophysiology studies, but its routine use is not yet established.


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