Disorders of Cardiac
Conduction and Rhythm
Pathophysiology
Dr. Patti Landerfelt
Chapter 28
Conduction System of the Heart
• Sinoatrial (SA) node – pacemaker of the heart
• Intrinsic rate 60-100 bpm
• Atrioventricular (AV) node
• Pauses electrical impulse to allow action potential
to spread across atria for coordinated contraction
• Intrinsic rate 45-50 bpm
• Bundle of His
• Bundle branches
• Purkinje fibers
• Intrinsic rate 15-40 bpm
Action Potentials
• Membrane potential: electrical potential
(difference) across the cell membrane
• During depolarization the membrane
potential becomes less negatively charged as
Na+ ions rapidly rush into the cell
• During repolarization, K+ ions leave the cell to
reestablish the resting membrane potential
• The Na+/K+ ATPase pump functions to
maintain resting membrane potential
Action Potentials
• Absolute refractory period –
action potential cannot be
initiated
• Relative refractory period –
action potential can be
initiated with a “larger than
normal” stimulus
Assessment of Coronary Blood Flow and Perfusion: Electrocardiogram
Electrocardiogram
P-wave: atrial depolarization, QRS complex: ventricular depolarization; T wave: ventricular repolarization
Why do we monitor the ECG?
• Advantages of continuous cardiac monitoring
• More sensitive to changes related to myocardial ischemia or arrhythmias than
patient report
• More accurate and timely detection of ischemic events that can predict early
complications
Normal Sinus Rhythm
• Sinus node fires 60–100
beats/minute
• Follows normal conduction
pattern
• Regular rhythm
• R – R distance regular
• P wave before each QRS complex
• P wave normal shape and
duration
• P-R interval normal
• QRS complex normal shape and
duration
Sinus Bradycardia
• Sinus node fires < 60
beats/minute
• Follows normal
conduction pattern
• Regular rhythm
• R – R distance regular
• P wave before each
QRS complex
• P wave normal shape
and duration
• P-R interval normal
• QRS complex normal
shape and duration
Sinus Tachycardia
• Sinus node fires > 100
beats/minute
• Follows normal
conduction pattern
• Regular rhythm
• R – R distance regular
• P wave before each QRS
complex
• P wave normal shape
and duration
• P-R interval normal
• QRS complex normal
shape and duration
Arrhythmias of
Atrial Origin
• Atrial flutter
• Rapid atrial ectopic tachycardia
• Atrial rate 240-340 bpm
• QRS may be normal or abnormal
• Occurs after corrective surgery for
congenital heart disease
Arrhythmias
of Atrial
Origin
• Atrial fibrillation
• Rapid, disorganized atrial activation
• Atrial rate 400-600 bpm
• Risks: CAD, mitral valve disease, MI, hypertension,
pericarditis, HF, hyperthyroidism
• Symptoms: palpitations, pulmonary edema, fatigue
• ↑ risk for thrombus formation  stroke
• Supraventricular tachycardia (SVT)
Arrhythmias of Atrial
Origin
• Paroxysmal Supraventricular tachycardia (PSVT)
• Tachyarrhythmia that originates above Bundle of His
• Sudden onset and termination
• Rate: 140-240 bpm
• Symptoms: sudden awareness of rapid heartbeat, brief
shortness of breath
• Can occur in otherwise healthy individuals
Ventricular Arrhythmias
– Medical Emergencies
• Ventricular tachycardia (VT)
• Cardiac rhythm originating after the
bundle of His
• Ventricular rate 70-250 bpm
• + pulse or NO PULSE
• Dangerous rhythm: Eliminates atrial
filling, decreases diastolic filling time 
severely limited or no cardiac output
Ventricular
Arrhythmias –
Medical
Emergencies
• Ventricular fibrillation (VF)
• Severe derangements of cardiac rhythm
• NO PULSE, no cardiac output
• Ventricle quivers rather than contracts
• Pulseless ventricular tachycardia and ventricular
fibrillation require immediate defibrillation
Treatment of Arrythmia Disorders
• Pharmacologic therapy and electrical interventions
• Cardiac pacemaker
• Slow heart rate (bradycardia)
• Delivers an electrical stimulus to the heart when normal pacemaker of heart is
defective
• Cardioversion
•
•
•
•
Synchronized cardioversion: Atrial fibrillation
Unsynchronized cardioversion or defibrillation: Pulseless VT or VF
Completely depolarizes the heart allowing SA node to regain control on the heart
Despite TV and movies – you cannot shock asystole
• Ablation: Destroying or removing arrhythmogenic tissue
• Surgery: Remove cause
• CABG, aneurysm removal
Thank you!
Questions/Concerns?
Please contact me:
patti.e.landerfelt@emory.edu