sinus node dysfunction

DR. ElSayed H

• 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

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.

• 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

• 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.

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.

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

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

etiology

• Intrinsic SNDAge-related changesCoronary artery diseaseGenetic 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]

• Various cardiomyopathies• Myocarditis• Pericarditis• Infiltrative heart diseases - Amyloidosis,

hemochromatosis, neoplasm• Collagen vascular diseases - Systemic lupus,

scleroderma• Neuromuscular diseases - Myotonic dystrophy,

Friedreich ataxia

Extrinsic SND

• Digitalis - Because of SN exit block• Propranolol• Verapamil• Quinidine• Procainamide• Lidocaine• Disopyramide• Reserpine

• Autonomic dysfunction

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

• About 50% of patients with SND develop tachy-brady syndrome over a lifetime

(higher risk of stroke and death)

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

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

Approach

• noninvasive methods • Laboratory studies: thyroid function serum electrolyte testing (Na+, K+, Ca2+)EchocardiographyTransesophageal atrial pacing: safe and inexpensive, (SN recovery time)

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

• 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

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.

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.

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

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.

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.

Tachy-brady syndrome

Holter Monitoring

• symptoms such as dizziness, presyncope, or syncope; these cannot be determined during an EP study,

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.

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

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.

• 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.

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

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

Class IIa indication

• For patients with minimal symptoms and a chronic heart rate of less than 40 bpm while awake

Class III indication

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