eMedicine Specialties > Cardiology > Arrhythmias

Sinus Node Dysfunction: Differential Diagnoses & Workup

Author: Yingbo Yang, MD, PhD, Clinical Assistant Professor of Cardiovascular Medicine, Division of Cardiology, Lawrence J Ellison Ambulatory Care Center, University of California, Davis, Medical Center
Coauthor(s): Yasir Batres, MD, Fellow, Division of Cardiology, University of California, Davis, Medical Center
Contributor Information and Disclosures

Updated: Aug 31, 2009

Differential Diagnoses

Atrial Fibrillation
Atrial Flutter
Atrioventricular Block

Other Problems to Be Considered

Premature ventricular beats in bigeminy may cause apparent slow pulse rate in physical examination.

Workup

Laboratory Studies

Because hypothyroidism and electrolyte imbalances can contribute to SND, thyroid function test and serum electrolyte test (Na+, K+ and Ca2+) can be useful.

Imaging Studies

  • No specific imaging studies are required in the initial workup of SND.
  • An echocardiogram should be considered because it can document the presence of underlying valvular or ischemic heart disease.

Other Tests

Electrocardiograph recording studies

The electrocardiograph recording is the most important method for the diagnosis of SND. Depending on the level of clinical suspicion, the frequency of symptoms and symptom relationship to exertion, the following methods are often used in combination to establish the diagnosis. Because SND symptoms are often intermittent, long term monitoring with an event recorder or implantable loop recorder can be very useful.

  • ECG - 12-lead ECG recording
  • Holter - 24-48 hours continuous 3-lead ECG recording
  • Event recorder study - Symptom-triggered 1-lead ECG recording during a 2-3 month period
  • Implantable loop recorder study - Predefined parameters that trigger single-lead electrocardiograph recordings for up to 3 years duration (These parameters may include bradycardia, tachycardia, pauses, and symptoms.)
  • Exercise testing - ECG recordings during exercise to evaluate maximal heart rate at peak exercise

The ECG criteria for SND diagnosis include the following:

  • Inappropriate sinus bradycardia: The arbitrary cutoff for a low sinus rate in a person at rest but awake is usually defined as <55-60 bpm. However, a study in 500 healthy subjects suggests the low afternoon sinus rate for men and women should be around 46 and 51 bpm respectively.13 Asymptomatic isolated sinus bradycardia is not an indication for pacemaker therapy.
  • Sinus pause or arrest
    • Sinus pause or arrest is defined as absence of sinus P waves on the ECG for more than 2 seconds due to a lack of sinus nodal pacemaker activity. The duration of the pauses should have no arithmetical relationship to the baseline sinus rate (ie, the P-P interval should not be an interval of the pause), otherwise the diagnosis of sinoatrial exit block should be considered.
    • A sinus pause of 2 seconds is not unusual in a healthy person.14 However, a sinus pause of more than 3 seconds is very uncommon except under certain conditions, such as sleep apnea, hypervagotonia state, or seizure activity.14
  • Sinoatrial exit block (SA exit block)
    • First-degree SA exit block reflects a conduction delay between the sinus node and atrium that cannot be recognized on regular ECG recordings.
    • Second-degree SA exit block reflects intermittent conduction block between the sinus node and atrium. It has 2 classic types and likely some atypical types. Only the classic types can be recognized on regular ECG recordings.
    • Type I (Wenckebach type) is manifested as group beating, which is progressive shortening of the P-P intervals, and then a pause that is less than twice the shortest P-P interval.
    • Type II is manifested as a pause that is a multiple of the baseline sinus P-P interval.
    • Third-degree SA exit block reflects complete conduction block from sinus node to atrium. It cannot be definitely distinguished from sinus arrest on regular ECG recordings.
  • Chronotropic incompetence: Chronotropic incompetence is defined as failure to achieve 70-80% of maximal predicted heart rate (maximal predicted heart rate = 220-age) at peak exercise. The clinical value of this definition, however, has not been well validated.15 The peak exercise heart rate can be influenced by multiple factors.

Pharmacological stimulation tests

Due to its moderate sensitivity and specificity for SND diagnosis, intrinsic heart rate and atropine stimulation tests are occasionally used as accessory tests in selected patients (such as patients with suspected hypervagotonia). The value of isoproterenol, propranolol, and adenosine stimulation tests in SND diagnosis is more controversial.

  • Intrinsic heart rate (IHR): Atropine (0.04 mg/kg) and propranolol (0.2 mg/kg) have been used to pharmacologically denervate the sinus node, which is then followed 5-20 minutes later by an evaluation of its IHR. The IHR in a healthy person is approximately equal to 117.2 – [0.53 x Age].16 Intrinsic SND is presumed to be present if the sinus rate after medications is below calculated IHR. Patients with mild SND may have a normal or exacerbated response. This test is probably helpful in patients with sinus bradycardia due to suspected hypervagotonia17 , in whom the IHR is expected to be normal.
  • Atropine test: Atropine alone (up to 0.04 mg/kg) may provide as much information as the combination of atropine (0.04 mg/kg) and propranolol (0.2 mg/kg).18 Atropine (1-3 mg) is the most commonly used agent to assess the parasympathetic tone. A normal response is an increase in sinus rate above 90 bpm or an increase of more than 25% above the baseline sinus rate.15 Patients with symptomatic sinus node dysfunction usually demonstrate a decrease in IHR. However, patients with only mild SND may have a normal or exacerbated response to atropine.

Electrophysiological study (EPS)

Due to its moderate sensitivity and specificity for SND diagnosis, EPS is only occasionally used when other tests yield ambiguous results.

Corrected sinus node recovery time (CSNRT): CSNRT is the most commonly used method in EPS for diagnosing SND.

At a site close to the sinus node, sinus rhythm is overdrive paced at different rates for one minute. The overdrive pacing rate starts at a rate just above basal sinus rate, and increases by 10-20 bpm with each successive overdrive pacing cycle until the overdrive pacing rate reaches 200 bpm. At each overdrive pacing cycle, the sinus node recovery time is measured as the time from the last paced atrial beat to the first post-paced spontaneous sinus beat. The corrected sinus node recovery time at each overdrive pacing cycle is calculated as follows:

Corrected sinus node recovery time = Sinus node recovery time – Basal sinus cycle length before the overdrive pacing

For normal sinus nodes, the maximal corrected sinus node recovery time should be less than 450 ms.18 In the THEOPACE study, patients with syncope and CSNRT ≥800 ms treated with permanent pacemaker had a 25% reduction of syncope over 4 years as compared with patients treated with theophylline or no therapy.19

Sinus node conduction time (SNCT) is another EPS parameter used in evaluating sinus node function.18 It is used less frequently than CSNRT.

Procedures

Pacemaker implant

More on Sinus Node Dysfunction

Overview: Sinus Node Dysfunction
Differential Diagnoses & Workup: Sinus Node Dysfunction
Treatment & Medication: Sinus Node Dysfunction
Follow-up: Sinus Node Dysfunction
References
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References

  1. Ferrer MI. The sick sinus syndrome in atrial disease. JAMA. Oct 14 1968;206(3):645-6. [Medline].

  2. [Guideline] Epstein AE, DiMarco JP, Ellenbogen KA, Estes NA 3rd, Freedman RA, Gettes LS, et al. ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the ACC/AHA/NASPE 2002 Guideline Update for Implantation of Cardiac Pacemakers and Antiarrhythmia Devices) developed in collaboration with the American Association for Thoracic Surgery and Society of Thoracic Surgeons. J Am Coll Cardiol. May 27 2008;51(21):e1-62. [Medline].

  3. Dobrzynski H, Boyett MR, Anderson RH. New insights into pacemaker activity: promoting understanding of sick sinus syndrome. Circulation. Apr 10 2007;115(14):1921-32. [Medline].

  4. Rodriguez RD, Schocken DD. Update on sick sinus syndrome, a cardiac disorder of aging. Geriatrics. Jan 1990;45(1):26-30, 33-6. [Medline].

  5. Menozzi C, Brignole M, Alboni P, Boni L, Paparella N, Gaggioli G, et al. The natural course of untreated sick sinus syndrome and identification of the variables predictive of unfavorable outcome. Am J Cardiol. Nov 15 1998;82(10):1205-9. [Medline].

  6. Simon AB, Janz N. Symptomatic bradyarrhythmias in the adult: natural history following ventricular pacemaker implantation. Pacing Clin Electrophysiol. May 1982;5(3):372-83. [Medline].

  7. Alt E, Völker R, Wirtzfeld A, Ulm K. Survival and follow-up after pacemaker implantation: a comparison of patients with sick sinus syndrome, complete heart block, and atrial fibrillation. Pacing Clin Electrophysiol. Nov 1985;8(6):849-55. [Medline].

  8. Lamas GA, Lee KL, Sweeney MO, Silverman R, Leon A, Yee R, et al. Ventricular pacing or dual-chamber pacing for sinus-node dysfunction. N Engl J Med. Jun 13 2002;346(24):1854-62. [Medline].

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  10. Jones SA, Boyett MR, Lancaster MK. Declining into failure: the age-dependent loss of the L-type calcium channel within the sinoatrial node. Circulation. Mar 13 2007;115(10):1183-90. [Medline].

  11. Hocini M, Sanders P, Deisenhofer I, Jaïs P, Hsu LF, Scavée C, et al. Reverse remodeling of sinus node function after catheter ablation of atrial fibrillation in patients with prolonged sinus pauses. Circulation. Sep 9 2003;108(10):1172-5. [Medline].

  12. Stein R, Medeiros CM, Rosito GA, Zimerman LI, Ribeiro JP. Intrinsic sinus and atrioventricular node electrophysiologic adaptations in endurance athletes. J Am Coll Cardiol. Mar 20 2002;39(6):1033-8. [Medline].

  13. Spodick DH. Normal sinus heart rate: sinus tachycardia and sinus bradycardia redefined. Am Heart J. Oct 1992;124(4):1119-21. [Medline].

  14. Hilgard J, Ezri MD, Denes P. Significance of ventricular pauses of three seconds or more detected on twenty-four-hour Holter recordings. Am J Cardiol. Apr 1 1985;55(8):1005-8. [Medline].

  15. Katritsis D, Camm AJ. Chronotropic incompetence: a proposal for definition and diagnosis. Br Heart J. Nov 1993;70(5):400-2. [Medline].

  16. Jose AD, Collison D. The normal range and determinants of the intrinsic heart rate in man. Cardiovasc Res. Apr 1970;4(2):160-7. [Medline].

  17. Jordan JL, Yamaguchi I, Mandel WJ. Studies on the mechanism of sinus node dysfunction in the sick sinus syndrome. Circulation. Feb 1978;57(2):217-23. [Medline].

  18. Josephson, ME. Clinical Cardiac Electrophysiology. 3rd edition. 2002.

  19. Alboni P, Menozzi C, Brignole M, Paparella N, Gaggioli G, Lolli G, et al. Effects of permanent pacemaker and oral theophylline in sick sinus syndrome the THEOPACE study: a randomized controlled trial. Circulation. Jul 1 1997;96(1):260-6. [Medline].

  20. Rosenqvist M, Obel IW. Atrial pacing and the risk for AV block: is there a time for change in attitude?. Pacing Clin Electrophysiol. Jan 1989;12(1 Pt 1):97-101. [Medline].

  21. Brandt J, Anderson H, Fåhraeus T, Schüller H. Natural history of sinus node disease treated with atrial pacing in 213 patients: implications for selection of stimulation mode. J Am Coll Cardiol. Sep 1992;20(3):633-9. [Medline].

  22. Andersen HR, Thuesen L, Bagger JP, Vesterlund T, Thomsen PE. Prospective randomised trial of atrial versus ventricular pacing in sick-sinus syndrome. Lancet. Dec 3 1994;344(8936):1523-8. [Medline].

  23. Lamas GA, Lee KL, Sweeney MO, Silverman R, Leon A, Yee R. Ventricular pacing or dual-chamber pacing for sinus-node dysfunction. N Engl J Med. Jun 13 2002;346(24):1854-62. [Medline].

  24. Sweeney MO, Bank AJ, Nsah E, Koullick M, Zeng QC, Hettrick D, et al. Minimizing ventricular pacing to reduce atrial fibrillation in sinus-node disease. N Engl J Med. Sep 6 2007;357(10):1000-8. [Medline].

  25. Lamas GA, Knight JD, Sweeney MO, Mianulli M, Jorapur V, Khalighi K, et al. Impact of rate-modulated pacing on quality of life and exercise capacity--evidence from the Advanced Elements of Pacing Randomized Controlled Trial (ADEPT). Heart Rhythm. Sep 2007;4(9):1125-32. [Medline].

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Further Reading

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Keywords

sick sinus syndrome, sinus node dysfunction, SND, sinoatrial disease, sinoatrial dysfunction, sluggish sinus syndrome, sinus nodal dysfunction, Valsalva maneuver, carotid sinus massage, idiopathic degenerative disease, coronary artery disease, autonomic hyperactivity, intrinsic sinus nodal dysfunction, infiltrative diseases, cardiomyopathy, hypertension, collagen vascular diseases, congenital heart disease, heart transplant, musculoskeletal disorders, myocarditis, pericarditis, beta-blockers, nondihydropyridine calcium channel blockers, cardiac glycosides, sympatholytic antihypertensives, membrane-active antiarrhythmics, autonomic dysfunction, vasovagal syncope, carotid sinus syndrome, extrinsic sinus nodal dysfunction, electrolyte imbalance, hypothyroidism, hyperthyroidism, hypothermia, sepsis

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Contributor Information and Disclosures

Author

Yingbo Yang, MD, PhD, Clinical Assistant Professor of Cardiovascular Medicine, Division of Cardiology, Lawrence J Ellison Ambulatory Care Center, University of California, Davis, Medical Center
Yingbo Yang, MD, PhD is a member of the following medical societies: American College of Cardiology and Heart Rhythm Society
Disclosure: Nothing to disclose.

Coauthor(s)

Yasir Batres, MD, Fellow, Division of Cardiology, University of California, Davis, Medical Center
Yasir Batres, MD is a member of the following medical societies: American College of Cardiology
Disclosure: Nothing to disclose.

Medical Editor

Justin D Pearlman, MD, PhD, ME, MA, Director of Advanced Cardiovascular Imaging, Professor of Medicine, Professor of Radiology, Adjunct Professor, Thayer Bioengineering and Computer Science, Dartmouth-Hitchcock Medical Center
Justin D Pearlman, MD, PhD, ME, MA is a member of the following medical societies: American College of Cardiology, American College of Physicians, American Federation for Medical Research, International Society for Magnetic Resonance in Medicine, and Radiological Society of North America
Disclosure: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Brian Olshansky, MD, Professor of Medicine, Department of Internal Medicine, University of Iowa College of Medicine
Brian Olshansky, MD is a member of the following medical societies: American Autonomic Society, American College of Cardiology, American College of Chest Physicians, American College of Physicians, American College of Sports Medicine, American Federation for Clinical Research, American Heart Association, Cardiac Electrophysiology Society, Heart Rhythm Society, and New York Academy of Sciences
Disclosure: Guidant/Boston Scientific Honoraria Speaking and teaching; Medtronic Honoraria Speaking and teaching; Guidant/Boston Scientific Consulting fee Consulting; Reliant Grant/research funds Other; Novartis Honoraria Speaking and teaching; Novartis Consulting fee Consulting

CME Editor

Amer Suleman, MD, Consultant in Electrophysiology and Cardiovascular Medicine, Department of Internal Medicine, Division of Cardiology, Medical City Dallas Hospital
Amer Suleman, MD is a member of the following medical societies: American College of Physicians, American Heart Association, American Institute of Stress, American Society of Hypertension, Federation of American Societies for Experimental Biology, Royal Society of Medicine, and Society of Cardiac Angiography and Interventions
Disclosure: Nothing to disclose.

Chief Editor

Michael E Zevitz, MD, Assistant Professor of Medicine, Finch University of the Health Sciences, The Chicago Medical School; Consulting Staff, Private Practice
Michael E Zevitz, MD is a member of the following medical societies: American College of Cardiology, American College of Physicians, American Medical Association, and Michigan State Medical Society
Disclosure: Nothing to disclose.

 
 
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