Sick sinus syndrome

sick sinus syndrome and heart blocks

1. sinus node dysfunction  DR. ElSayed H

2.  a group of heart rhythm problems (arrhythmias) in which the sinus node — the heart's natural pacemaker — doesn't work properly . SN impulse formation and propagation 

3. TYPES OF SA NODAL DYSFUNCTION Sinus pause or arrest  : transient absence of sinus P waves on the electrocardiogram (ECG) that may last from two seconds to several minutes  no arithmetical relationship to the basic sinus rate.

4. SA nodal exit block   Sinus arrhythmia  : small changes in the sinus cycle length variation in the P-P interval by 0.12 sec (120 msec ) or more in the presence of normal P waves and the usual PR interval or a difference of 10 percent or greater between the longest and shortest P-P intervals

5. The sinus node (SN) is a subepicardial structure normally located in on the upper end of the sulcus terminalis . It is formed by a cluster of cells capable of spontaneous depolarization . Electrical impulses generated in the SN must be conducted outside the SN in to depolarize the rest of the heart. SN activity is regulated by the autonomic nervous system.

6. Pathophysiology SN impulse formation and propagation, which are often accompanied by similar abnormalities in the atrium and in the conduction system of the heart. may result in inappropriately slow ventricular rates and long pauses at rest or during various stresses.

7. When SND is mild, patients are usually asymptomatic. As SND becomes more severe, patients may develop symptoms due to organ hypoperfusion and pulse irregularity.

8. symptoms include : Fatigue Dizziness Confusion Fall Syncope Angina Heart failure symptoms and palpitations

9. etiology Intrinsic SND Age-related changes Coronary artery disease Genetic causes: defects in the sodium channel, calcium channel, hyperpolarization -activated cyclic nucleotide-gated cation (HCN) channel, ankyrin -B, and connexin 40) have been associated with familial sick sinus syndromes. [6]

10. Various cardiomyopathies Myocarditis Pericarditis Infiltrative heart diseases - Amyloidosis , hemochromatosis , neoplasm Collagen vascular diseases - Systemic lupus, scleroderma Neuromuscular diseases - Myotonic dystrophy, Friedreich ataxia

11. Extrinsic SND Digitalis - Because of SN exit block Propranolol Verapamil Quinidine Procainamide Lidocaine Disopyramide Reserpine

12. Autonomic dysfunction

13. Morbidity and mortality Sudden cardiac death (rare) Syncope Fall Thromboembolic events, including stroke - Especially in patients with tachy-brady syndrome CHF Exercise intolerance Cardiac dysfunction due to bradycardia and loss of AV synchrony Atrial tachyarrhythmias - Such as atrial flutter or fibrillation

14. About 50% of patients with SND develop tachy-brady syndrome over a lifetime ( higher risk of stroke and death)

15. symptoms Specific of SND include the following: Cerebral symptoms - Irritability, labile mood swings, forgetfulness, dizziness, slurred speech, blanking periods, falls, and syncope Cardiac symptoms - Palpitations, angina, CHF symptoms, and sudden cardiac death (rare) Vague gastrointestinal symptoms and oliguria Patients with tachy-brady syndrome may have symptoms of stroke or transient ischemia attack (TIA) Exercise intolerance Fatigue Shortness of breath with or without palpitations

16. Physical Examination slow heart rate Carotid sinus massage may reveal sinus pause of more than 3 seconds and/or hypotension symptoms in patients with carotid sinus hypersensitivity . signs and symptoms of CHF

17. Approach noninvasive methods  Laboratory studies: thyroid function  serum electrolyte testing (Na + , K + , Ca 2 + ) Echocardiography Transesophageal atrial pacing: safe and inexpensive,   (SN recovery time)

18. Electrocardiography  criteria for SND include the presence of 1 or more of the following: Sinus bradycardia below the heart rate expected for age - Ie , under 100 beats per minute ( bpm ) in an infant, under 80 bpm in a preschool child, under 60 bpm in a school child, and under 50 bpm in an adolescent

19. Sinus pause or absence of an expected P wave for more than 3 seconds). Slow escape rhythms that originate within the atria, His bundle, or ventricles. Marked sinus arrhythmia with constant variation in the P-P interval, which is likely to be accompanied by sinus bradycardia . Presence of both bradyarrhythmias and tachyarrhythmias

20. Sinus pause or arrest defined as absence of sinus P waves on the electrocardiogram (ECG) for more than 2 seconds due to a lack of sinus nodal pacemaker activity.

21. Sinoatrial exit block First-degree sinoatrial (SA) exit block reflects a conduction delay between the SN and the atrium that cannot be recognized on regular electrocardiographic recordings .

22. Second-degree Second-degree SA exit block reflects intermittent conduction block between the SN and the atrium. It has 2 classic types and likely some atypical types. Only the classic types can be recognized on regular electrocardiographic recordings. They are as follows: Type I ( Wenckebach type) - 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 - Manifested as a pause that is a multiple of the baseline sinus P-P interval

23. Third-degree SA exit block Third-degree SA exit block reflects complete conduction block from the SN to the atrium. It cannot be definitely distinguished from sinus arrest on regular electrocardiographic recordings. An atrial, junctional, or ventricular escape rhythm is present.

24. Chronotropic incompetence SND usually have a blunted response an exercise stress test can determine whether chronotropic incompetence is present . defined as failure to achieve 70-80% of maximal predicted heart rate (maximal predicted heart rate = 220 - age) at peak exercise. 

25. Tachy-brady syndrome

26. Holter Monitoring symptoms such as dizziness, presyncope , or syncope; these cannot be determined during an EP study,

27. Pharmacologic Stimulation Tests  moderate sensitivity and specificity for SND diagnosis intrinsic heart rate and atropine stimulation tests the value of isoproterenol , propranolol , and adenosine stimulation tests in SND diagnosis is more controversial.

28. Electrophysiologic Studies EP studies are indicated in patients with signs of bradyarrhythmias (mainly syncope) in whom bradycardia could not be documented during Holter monitoring. Classic EP criteria for SND include the presence of 1 or more of the following: Corrected SN recovery time (CSNRT) greater than 275 milliseconds SA conduction time greater than 200 milliseconds SA node arrest SA exit block SN reentry tachycardia

29. Treatment No treatment is required for asymptomatic patients. Acute treatment consists of atropine (0.04 mg/kg intravenously every 2-4 h) and/or isoproterenol (0.05-0.5 mcg/kg/min intravenously). A transvenous temporary pacemaker sometimes is required despite medical therapy.

30. Pacemaker therapy is the only effective surgical care for patients with chronic, symptomatic SND . goal of pacemaker therapy in patients with SND is to relieve symptoms.

31. Pacemaker indications Class I indication  : documented symptomatic sinus bradycardia , sinus pause, and chronotropic incompetence; this includes patients who have iatrogenic SND secondary to essential medications for which no acceptable alternatives exist

32. Class IIa indication   : patients with SND and a sinus rate below 40 bpm when a clear association between symptoms ( ie , symptoms consistent with bradycardia ) and bradycardia has not been documented. patients with syncope of unexplained origin when clinically significant abnormalities of SN are discovered or provoked in EP studies

33. Class IIa indication For patients with minimal symptoms and a chronic heart rate of less than 40 bpm while awake

34. Class III indication  Pacemaker therapy is contraindicated in patients with asymptomatic SND or symptomatic bradycardia due to medications that are not essential.