Bradycardias

Salah Abusin, MBBS, MRCP (UK), ABIMCardiology Fellow

Chicago, IL,USA

Bradycardias

• SA node dysfunction or Sick Sinus Syndrome– Inappropriate sinus

bradycardia– Sinoatrial exit Block– Sinus Pause/Arrest– Tachycarda/Bradycardia

syndrome– Persistent Atrial Standstill

• AV Blocks– First Degree– Second Degree

• Mobitz I• Mobitz II• 2:1 Block

– Third Degree– High Grade AV Block

Sinoatrial Node dysfunction

• Inappropriate sinus bradycardia• Sinoatrial exit Block• Sinus Pause/Arrest• Tachycarda/Bradycardia syndrome

Causes - Intrinsic• Idiopathic degenerative disease• Coronary Artery Disease• Cardiomyopathy• Hypertension• Infiltrative Disorders (amyloidosis etc..)• Collagen Vascular Disorders (scleroderma etc.)• Inflammatory Processes (myocarditis)• Surgical Trauma• Musculoskeletal disorders (myotonic dystrophy)• Congenital heart disease (postoperative or

absence of correction)

Causes – Extrinsic - 1

• Medication– BBs, CCBs, digoxin– Clonidine, alpha methyldopa, reserpine– Antiarrhythmics Type• IA (quinidine, procainamide)• IC (flecainide) • III (amiodarone)

– Lithium

Causes – Extrinsic - 2

• Autonomic influences– High vagal tone– Carotid sinus syndrome– Vasovagal syncope

• Electrolyte abnormalities– Hyperkalemia, hypercarbia, hypothyroidism

• Increase intracranial pressure• Hypothermia• Sepsis

Sinoatrial Node dysfunction

• Inappropriate sinus bradycardia• Sinus Pause/Arrest• Sinoatrial exit Block• Tachycarda/Bradycardia syndrome

Inappropriate Sinus Bradycardia Chronotropic Incompetence

• HR<60 that doesn’t increase appropriately with exercise

• Usually defined as failure to attain 80% of maximal age predicted HR (MAHR) on exercise testing

• MAHR = 220 – Age• e.g. failure to reach a HR of 120 in a 70 year old

patient

Sinus bradycardia

Sinoatrial Node dysfunction

• Inappropriate sinus bradycardia• Sinus Pause/Arrest• Sinoatrial exit Block• Tachycarda/Bradycardia syndrome

Sinus Pause/Arrest

• Defined as absence of a sinus beat for >=3 seconds while AWAKE

• SA node fails to discharge so no atrial activity occurs

Sinus Pause/Arrest

Sinoatrial Node dysfunction

• Inappropriate sinus bradycardia• Sinus Pause/Arrest• Sinoatrial exit Block• Tachycarda/Bradycardia syndrome

Sinoatrial Exit Block

• SA node discharges an impulse that does NOT result in atrial activity

Sinoatrial Exit Block

Sinoatrial Node dysfunction

• Inappropriate sinus bradycardia• Sinus Pause/Arrest• Sinoatrial exit Block• Tachycarda/Bradycardia syndrome

Tachycardia-Bradycardia Syndrome

• Bradycardia/sinus pauses interspersed with atrial arrhythmias (AFL, A fib, A tach)

• Sinus arrest manifests after termination of atrial arrhythmia (spontaneously or after DCCV)

• Sinus Node Recovery Time (SNRT) uses the above observation to assess SA node function in EP studies

Tachycardia-Bradycardia Syndrome

Hurst the Heart12th Edition

Indications for pacing in SND

• Class I (recommended)– SND with documented symptoms– SND due to irreversible factors or due to essential

drug therapy– Chronotropic incompetence

• Class III (NOT recommended)– Asymptomatic

Bradycardias

• SA node dysfunction or Sick Sinus Syndrome– Inappropriate sinus

bradycardia– Sinoatrial exit Block– Sinus Pause/Arrest– Tachycarda/Bradycardia

syndrome– Persistent Atrial Standstill

• AV Blocks– First Degree– Second Degree

• Mobitz I• Mobitz II• 2:1 Block

– Third Degree– High Grade AV Block

AV Blocks

• First Degree• Second Degree– Mobitz I– 2:1 Block– Mobitz II

• Third Degree• High Grade AV Block

First Degree AV Block

• PR interval > 200msec• If QRS is normal, block is usually at the level of

the AV node• If QRS shows bundle branch block, block

maybe in His-Purkinje System

First degree AV block

Management

• Usually no specific therapy is required

Second Degree Heart BlockMobitz I or Wenchebach

• Progressive Prolongation of the PR interval and shortening of the RR interval until a P wave is blocked

• RR interval containing the non conducted P wave is less than two PP intervals

• PR interval longer after the non conducted P wave

• Grouped beating

Second Degree – Mobitz I

P P P P P P

Causes• Normal• Athletes• Medications• Myocardial Infarction

(inferior wall)• Acute rheumatic fever• Myocarditis

Features• Usually asymptomatic• Usually narrow QRS complex

block at AV node• The presence of bundle branch

block suggests the possibility of block below the AV node in His Purkinje system

Management

• Usually do not require permanent pacing

Second Degree – Mobitz II

• Constant PR interval with intermittent nonconducted P wave and no evidence for PACs

• RR interval between non conducted P waves is equal to two PP intervals

• Each QRS is preceded by multiple P waves • 3:1, 4:1 also called high grade AV block• Other variations include 3:2 • 2:1 block maybe Mobitz I or Mobitz II

3:2 AV Block

• Add ECG example here

High Grade AV Block

PP PP

Second Degree Heart Block2:1 Block

Management

• Usually require permanent pacing especially if symptomatic due to high likelihood of progression to high grade AV block and third degree AV block

Differentiating mechanism of 2:1 blockFeature Mobitz I Mobitz IIQRS duration Narrow WideResponse to increasing HR & AV conduction i.e. exercise, atropine

Improves Worsens

Response to decreasing HR & AV conduction i.e. carotid sinus massage

Worsens Improves

Acute MI Inferior Anterior

Third Degree AV block

• Atrial impulses consistently fail to reach the ventricles, resulting in atrial and ventricular rhythms that are independent of each other

• PR interval varies• PP and RR intervals are constant• Ventriculophasic sinus arrhythmia– PP interval containing QRS is shorter than PP

interval without a QRS complex

Third Degree AV block

P P P P P P P P P PP

Escape Rhythms

• Junctional– Usually narrow (may be wide if underlying BBB)– 40-60/min

• Ventricular Escape Rhythm– Wide complex – 30-40/min (range 20-50)

Causes

• Myocardial Infarction– Inferior wall, usually transient, associated with a

stable junctional escape rhythm – Anterior wall, usually permanent

• Degenerative Disease• Infiltrative Disease (amyloid, sarcoid)• Endocarditis (Aortic Root abscess)• Hyperkalemia• Medication• Post Cardiac Surgery

Management

• Usually require permanent pacing

Acclerated Idioventricular rhythm

Acclerated Idioventricular rhythm

• Regular Wide complex rhythm• 60-110/min• AV dissociation• Benign phenomenon• Causes– Normal– Coronary reperfusion– Digoxin toxicity

Problems

3rd degree AV block, junctional escape

Second Degree Mobitz I

P P P P P P P P P P P

3rd degree AV block, junctional escape

P P P P P P P P P P

3rd degree AV block, junctional escapeor high grade AV block

Problem

• 50 year old female with no PMH presents with acute onset of shortness of breath on exertion of 4 days duration

• HR 50/min, BP 140/80• Initial ECG sinus bradycardia• TropI 1.2

Sinus arrest with ventricular escape

Sinus arrhythmia

Problem

• 65 year old male presented with 4 day history of shortness of breath on exertion, orthopnea and PND

• HR 50/min, regular, BP 150/70

Atrial Fibrillation with 3rd degree AV block & junctional escape

Thank You