Arrhythmias

Rhythms and Arrhythmia

• SA Node– Normal sinus rhythm– Sinus Bradycardia– Sinus Tachycardia– Sick Sinus Syndrome

• Atria– Ectopic beats– Fibrillation– Flutter– Supraventricular tachycardia

Rhythms and Arrhythmia

• AV Node– Reentrant tachycardia– 1st 2nd 3rd degree blocks– Bundle branch block

• Ventricles– Ectopic beats– Tachycardia– Preexitation– Ischemia

Normal Sinus Rhythm

• Normal sequence of conduction, originating in the sinus node and proceeding to the ventricles via the AV node and His-Purkinje system.

• EKG Characteristics: Regular narrow-complex rhythm

Sinus Tachycardia Aetiologies• Fever• Hyperthyroidism• Hypovolaemia• Anxiety• Pheochromocytoma• Sepsis• Anaemia• Exposure to stimulants (nicotine, caffeine) or illicit drugs (amphetamines)• Hypotension and shock• Pulmonary embolism• Acute coronary ischemia and myocardial infarction• Heart failure• Chronic pulmonary disease• Hypoxia

http://www.youtube.com/watch?v=zbDtMtJyVtI

Sinus Bradycardia

• Sinus Bradycardia– HR< 60 bpm– QRS is narrow and preceded by p wave– Can be normal in well-conditioned athletes at rest

or children during sleep– So when is it not normal?– Is not normal if the sinus rhythm can’t increase

with exercise

Sinus Bradycardia - aetiologies

• Normal aging• 15-25% following AMI• Sick sinus syndrome• Hypothyroidism• Hypothermia• Hypokalemia • Situational: micturation, coughing• Drugs: beta-blockers, digoxin, calcium channel blockers,

amiodarone, lithium

http://www.youtube.com/watch?v=Yff9VvNGL5w&feature=related

Sick Sinus Syndrome• Aetiology

– Fibrosis– Atheroschlerosis of RC artery– SLE, collagen vasc diseases– Chagas disease - yeay– Injury, heart surgery– Infiltrative diseases

• sarcoid• amyloid

• Symptoms– Weakness– Palpitations– Syncope

Disorders of the SA Node

• Sinus arrest

• Tachycardia-bradycardia syndrome– Alternating brady-tachy causing palpitations

• SA exit block– Normal SA impulse but conduction to atria is

impaired

Atrial Ectopic Beats

• Ectopic P waves look abnormal• SA node continues regardless in compensatory delay• SA node timing is reset if premature SA firing caused by

ectopic – non compensatory

Atrial Fibrillation

• Constant conduction within the atria, multiple circuits, loss of contractility

• Can be paroxysmal, persistent or permanent• 1 in 5 strokes caused by AF: patients require anticoagulation

therapy to prevent clot formation

Atrial FibrillationRisk Factors Relative Risk

History of hypertension 1.6

Heart failure and/or reduced left ventricular function

1.4

Advanced age 1.4

Diabetes 1.7

Coronary artery disease 1.5

Atrial Flutter

• Aetiology– 30% have no underlying cardiovascular disease– 30% CAD– 30% hypertension

• Pathophysilogy– Single reentrant circuit around the tricuspid valve– Distinctive sawtooth ECG

Supraventricular Tachycardias

• Any tachycardic rhythm originating above the ventricles

• It usually involves ectopic pacemaker cells or an accessory (reentrant) pathway

• http://www.youtube.com/watch?v=Y7QdOBYeAS4

Mechanism of Reentry

• A: slow conduction, short RP• B: normal conduction and RP

SA Node Reentrant Tachycardia

AV Node Reentrant Tachycardia

• Aetiology– Formation of “beta” pathway

• Anxiety• Exertion• Caffeine, alcohol, drugs

• Pathophysiology– Dual pathways within AV node– Alpha: fast, long RP– Beta: slow, short RP

• Signs & Symptoms– Palpitation– Dizziness, syncope– Chest pain, angina (if coexisting CAD)

AV Node Reentrant Tachycardia

First Degree Block• If the PR interval is more than 1 small square then this is a 1st degree AV

block• Not associated with morbidity or mortality but heralds a more severe

block if MI occurs• Risk factor = age

Second Degree Block

• A conduction delay within the AV node causing increasingly lengthened PR intervals until the node cannot transmit the signal to the ventricles (the Wenkebach phenominum)

• Aetiology– Structural heart disease– Drugs: digoxin, Na, beta and Ca channel blockers, tricyclic

antidepressants & lithium at toxic levels– Metabolic: hyperkalaemia, hypermagnesaemia, hyperthyroidism,

Addison’s– Enhanced vagal tone due to pain, athletes at rest– A shit load more at

http://emedicine.medscape.com/article/161919-overview– Mostly intranodal but poor prognosis if infranodal

Second Degree Block

Type I Wenckebach: P waves shown by arrows, lengthening PR interval

Type II: P waves shown by arrows, unpredictable non-conduction and loss of QRS

Third Degree Heart Block

• Complete interruption of conduction from the atria

• Ventricles show escape rhythms• Aetiology– Infectious: Endocarditis, rheumatic fever– Neuromuscular: muscular dystrophy– Drugs (see 2nd degree HB)– Rheumatic, infiltrative, metabolic, electrolyte ...

Third Degree Heart Block

BBB

• Normal P waves• Normal PR interval• Widening of QRS to more than 0.12s because

of delayed depolarisation of the ventricle

Ventricular Ectopic BEats

• Premature beats originating within the myocardium

• Distinctive tall, wide beats precede the P wave

VT

• Reentrant arrhythmia as a result of scarring of the myocardium

• The rhythm can stabilise, revert spontaneously to sinus rhythm or lead to VF and death

Ventricular Preexitation

• Associated with WPW syndrome• Accessory pathway Bundle of Kent allows early

ventricular depolarisation forming a blunted Q wave called a delta wave and an abnormal T wave (last 2 beats below)

Myocardial Ischemia

• Myocardial ischemia caused by narrowing of the coronary arteries results in ST depression

• Below the depression is shown in the shaded areas

ECG Online Test

• http://www.andrews.edu/~schriste/HealthTeaching/Practice/Sinus_and_Atrial/si01.html