ECG Analysis and Arrhythmias

Arrhythmia Definitions

• Arrhythmia = lack of normal rhythm
• Dysrhythmia = rhythm doesn't work properly
• Tachyarrhythmia = fast arrhythmia
• Bradyarrhythmia = slow arrhythmia

Why Do We Care about Arrhythmias?

• Cardiac output (CO) = Stroke Volume x Heart Rate
• Bradyarrhythmias reduce heart rate, lowering cardiac output
• Tachyarrhythmias increase heart rate, increasing oxygen demand

Artifact

• Disruption in monitoring caused by external factors
• Common causes:
  • AC interference: 60 Hz artifact
  • Muscle contractions and tremors
  • Respiratory artifact: patient movement, wandering baseline
  • Loose electrode
  • Broken lead wire

Steps in Analyzing a 12-Lead ECG

• Orient yourself: Identify the leads and their positions
• Calculate Rate: Determine the heart rate per minute
• Determine Rhythm: Identify the regularity and origin of the rhythm
• Determine the Axis: Analyze the electrical direction of the heart
• Intervals and QRS Duration: Measure durations of PR, QRS, and QT intervals
• "Others": Assess ST segment and T wave morphology

Mechanisms of Arrhythmias

• Re-entry: A circuit where an impulse travels back on itself in the heart, creating a continuous loop, causing a rapid rhythm.
• Automaticity: An area within the heart that fires spontaneously, independent of the normal pacemaker (SA node).
• Triggered Activity: A heart cell is stimulated to fire repeatedly by delayed afterdepolarizations (DADs) and early afterdepolarizations (EADs).

Bradyarrhythmias

• Heart rate < 60 bpm
• Symptoms:
  • Dizziness, lightheadedness
  • Palpitations, pre-syncope
  • Syncope

Sinus Bradycardia (SB)

• Rate: < 60 bpm
• Symptoms:
  • Asymptomatic
  • Palpitations
  • Shortness of breath, fatigue
  • Syncope, lightheadedness

Sinus Tachycardia

• Rate: > 100 bpm
• Rhythm: Normal P waves precede every QRS complex
• Intervals: QRS normal, PR interval normal
• Causes:
  • Normal physiologic response to pain, exercise, stress, infection, anemia, hyperthyroidism, dehydration, pulmonary embolism
• Treatment: Identify and correct the underlying cause

Supraventricular Tachycardia (SVT)

• A rapid heart rhythm that originates above the ventricles
• Includes:
  • Atrial Flutter
  • Atrial Fibrillation
  • AVNRT
  • AVRT

Premature Atrial Contractions (PACs)

• Premature activation of the atria from an ectopic pacemaker
• Rate: Normal or accelerated
• Rhythm: Irregular
• Intervals:
  • P-R: Ectopic beats may have a different P-R interval
  • QRS: Usually normal
• Causes:
  • Occasional PACs are normal
  • More frequent in CHF, myocardial ischemia, COPD

Focal Atrial Tachycardia (FAT)

• Regular atrial rhythm originating from a site other than the SA node, with a rate > 100 bpm
• Rate: 150 - 250 bpm
• Rhythm: Regular
• Intervals: Narrow QRS, normal PR
• Treatment: Adenosine can reveal underlying atrial activity

AV Nodal Reentrant Tachycardia (AVNRT)

• Most common type of paroxysmal SVT
• Reentrant circuit at the AV node, causing simultaneous atrial and ventricular depolarization
• Rate: 150 - 250 bpm
• Rhythm: Regular
• Treatment:
  • Vagal maneuvers: Carotid sinus massage, coughing, Valsalva
  • Adenosine
  • Long-term: Ablation

AV Reentrant Tachycardia (AVRT)

• Involves a reentrant circuit via an accessory pathway (abnormal connection between atria and ventricles)
• Two conduction pathways: AV node (normal) and accessory pathway
• Retrograde P wave seen after the QRS
• QRS may be normal (orthodromic) or prolonged (antidromic)
• Treatment: Similar to AVNRT

Wolff-Parkinson-White Syndrome (WPW)

• Pre-excitation: Early ventricle activation due to impulses bypassing the AV node via an accessory pathway
• ECG Findings:
  • Shortened PR interval
  • Delta wave: Slurring slow rise of the initial portion of the QRS
  • QRS > 120 ms (when pre-excited)
  • ST Segment and T wave discordant changes
  • Treatment:
    • Catheter ablation
    • Vagal maneuvers
    • Medications: Adenosine, Verapamil, Procainamide

Atrial Fibrillation (A-Fib)

• Multiple atrial foci fire chaotically, causing rapid, irregular atrial activity
• Rate: Atria firing ~300 - 650 bpm
• Rhythm: Irregularly Irregular
• Intervals: PR unmeasurable, narrow QRS
• Causes:
  • Hypertension (most common)
  • COPD, CHF, underlying heart disease, aging, stress, infection, alcohol, thyrotoxicosis, caffeine

Atrial Fibrillation Management

• Rate control: Medications slow the ventricular rate:
  • Beta-blockers (Metoprolol)
  • Calcium Channel Blockers (Diltiazem)
  • Digoxin
• Rhythm control: Medications restore sinus rhythm:
  • Amiodarone, Sotalol, Flecainide
• Anticoagulation: Prevent cerebrovascular accident:
  • Warfarin, Enoxaparin, Rivaroxaban, Apixaban, Dabigatran
• Emergency: Electrical cardioversion (DCCV)
• Ablation: Pulmonary vein isolation

Atrial Flutter

• A rapid heart rhythm caused by a re-entry circuit in the right atrium, traversing the cavo-tricuspid isthmus
• Rate: Atrial rate ~ 300 bpm (range 200 - 350 bpm)
• Ventricular rate determined by the AV block ratio
• Rhythm: "Saw-tooth" pattern (flutter waves) in leads II, III, and aVF
• Intervals: PR unmeasurable, narrow QRS
• Treatment:
  • Difficult to control rate with medications
  • Anticoagulation
  • Cardioversion if unstable
  • Ablation of the cavo-tricuspid isthmus

Multifocal Atrial Tachycardia (MAT)

• Multiple atrial foci fire intermittently
• Rate: 100 - 250 bpm
• Rhythm: Irregular, ≥ 3 different p-wave shapes
• Intervals: QRS narrow, PR interval variable
• Causes: Most common in COPD, hypoxemia, hypomagnesemia, hypokalemia
• Treatment: Verapamil; treat the underlying cause

Premature Ventricular Contractions (PVCs)

• Ectopic beats originating below the bifurcation of the Bundle of His
• Wide QRS, usually without a preceding P wave
• Causes:
  • Electrolyte abnormalities, hypoxia, hyperthyroidism, catecholamines, drug toxicities
  • Can occur in normal or abnormal hearts
• Treatment:
  • If associated with acute MI, couplets, bigeminy, trigeminy, multifocal, frequent, or symptomatic

Monomorphic Ventricular Tachycardia

• Usually occurs in diseased hearts
• Rhythm: P-waves obscured or absent, unrelated to QRS complex
• Causes: CAD, acute MI, digitalis toxicity, CHF, ventricular aneurysms, cardiomyopathy, electrolyte abnormalities
• Treatment:
  • Symptomatic/Unstable: Electrical cardioversion
  • Medications: Amiodarone, Lidocaine

Ventricular Fibrillation (V Fib)

• Chaotic electrical activity from the ventricles, causing absence of cardiac output
• Treatment: Immediate defibrillation and ACLS protocols

Torsades de Pointes

• Upward and downward deflection of QRS complexes around the baseline
• P wave usually obscured, wide and bizarre QRS complex
• Causes: Drugs that prolong QT interval, MI, electrolyte imbalances (hypo-Mg, hypo-K, hypo-Ca)
• Treatment:
  • Synchronized cardioversion if unstable
  • IV Magnesium, IV Potassium
  • Overdrive pacing