What is the approach to assessing arrhythmias?

Approach to Assessment of Arrhythmias

Definition

Arrhythmias are abnormalities in cardiac rhythm resulting from disturbances in impulse formation, impulse conduction, or both, occurring in structurally normal or diseased hearts across all age ranges 1.

Classification

By Mechanism 1

• Automaticity: Abnormal spontaneous depolarization of cardiac cells
• Triggered activity: Afterdepolarizations (early or delayed) causing ectopic beats
• Reentry: Circular propagation of electrical impulse through myocardium

By Origin

• Supraventricular: Atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT)
• Ventricular: Premature ventricular contractions (PVCs), non-sustained ventricular tachycardia (NSVT), sustained ventricular tachycardia (VT), ventricular fibrillation (VF) 2

By Clinical Severity 3

• Hemodynamic impact: Related to heart rate (critical when RR interval shortens excessively) and loss of AV synchrony
• Prognostic significance: Benign vs. life-threatening arrhythmias

Differential Diagnosis

Structural Heart Disease 2

• Ischemic heart disease/prior myocardial infarction
• Cardiomyopathies (dilated, hypertrophic, arrhythmogenic)
• Valvular heart disease (particularly mitral stenosis) 4
• Congenital heart disease

Inherited Arrhythmic Syndromes 2

• Long QT syndrome
• Brugada syndrome
• Catecholaminergic polymorphic ventricular tachycardia
• Arrhythmogenic cardiomyopathy (AC)

Metabolic/Toxic 2

• Electrolyte disturbances (hypokalemia, hypomagnesemia)
• Drug-induced (QT-prolonging medications, antiarrhythmics causing proarrhythmia)
• Thyroid dysfunction

History

Character of Symptoms 2

• Palpitations: Rapid, irregular, or forceful heartbeats
• Syncope/presyncope: Sudden loss of consciousness or near-syncope
• Chest pain: Non-pleuritic chest discomfort
• Dyspnea: Shortness of breath at rest or with exertion
• Exercise-related symptoms: Symptoms during or immediately after physical activity 2

Red Flags (Arrhythmic Syncope) 2

• Syncope in supine position (not vasovagal)
• Syncope during or after exercise (suggests ventricular arrhythmia or channelopathy)
• No or only brief prodromal symptoms (distinguishes from vasovagal)
• Repetitive episodes without clear trigger
• Seizures: Resistant to treatment, occurring at night, precipitated by exercise/syncope/loud noise
• Drowning by competent swimmer (suggests arrhythmia)

Risk Factors 2, 4

• Family history: Sudden cardiac death in young relatives (<40 years), inherited arrhythmic syndromes
• Cardiac history: Prior myocardial infarction, heart failure, cardiomyopathy
• Medications: QT-prolonging drugs, diuretics (causing hypokalemia), CYP inhibitors, antiarrhythmics 2
• Age: Elderly patients have dramatically increased risk of ischemic heart disease 2
• NYHA functional class III-IV: Strong predictor of arrhythmias 4
• Structural abnormalities: Left atrial enlargement >48mm 4

Physical Examination (Focused)

Cardiovascular 2

• Pulse: Rate, rhythm (regular vs. irregular), character
• Blood pressure: Hypotension suggests hemodynamic compromise
• Jugular venous pressure: Elevated in heart failure, cannon A waves in AV dissociation
• Heart sounds: S3 (heart failure), murmurs (valvular disease), irregular rhythm
• Signs of heart failure: Peripheral edema, pulmonary crackles, hepatomegaly

General 2

• Vital signs: Tachycardia, bradycardia, hypotension
• Mental status: Altered if hemodynamically compromised
• Signs of thyroid disease: Tremor, exophthalmos, goiter

Investigations

Initial ECG Assessment 2

• 12-lead ECG in sinus rhythm (Class I): Look for structural heart disease, conduction disorders, QT prolongation, pre-excitation, Brugada pattern 2
• 12-lead ECG during tachycardia (Class I): Essential for wide complex tachycardia diagnosis 2

Ambulatory Monitoring 2

24-hour Holter monitoring 2:

• Use when symptoms occur at least once daily
• Quantifies PVC/NSVT burden
• Assesses response to antiarrhythmic therapy 2

Event/loop recorders 2:

• For sporadic symptoms (less than daily)
• Extended monitoring periods increase diagnostic yield
• Patient-activated or auto-triggered

Adhesive patch monitors 2:

• Continuous 1-lead monitoring up to 14 days
• Patient activation for symptoms
• Delayed analysis (patch must be returned)

Implantable loop recorders 2:

• For very infrequent symptoms (especially syncope)
• Monitoring period of 3-5 years
• 25% added diagnostic yield after negative external monitoring
• Reserved for patients with nonrevealing conventional monitoring

Exercise Testing 2

• Class I indication: VA symptoms with exertion, suspected ischemic heart disease, or catecholaminergic polymorphic VT 2
• Assesses exercise-induced arrhythmias
• Evaluates ischemia as trigger

Cardiac Imaging 2

Echocardiography (Class I) 2:

• Evaluate cardiac structure and function
• Left ventricular ejection fraction (LVEF)
• Valvular abnormalities
• Left atrial size (>48mm predicts arrhythmias) 4
• RV assessment in suspected arrhythmogenic cardiomyopathy

Cardiac MRI (Class IIa) 2:

• Suspected structural heart disease with non-diagnostic echocardiography
• Tissue characterization (fibrosis, infiltration)
• Arrhythmogenic cardiomyopathy diagnosis 2

Electrophysiologic Study 2

• Inducibility of sustained VT in high-risk patients
• Mechanism determination for complex arrhythmias
• Guide ablation therapy

Laboratory Tests 2

• Electrolytes: Potassium, magnesium, calcium
• Thyroid function: TSH, free T4
• Cardiac biomarkers: Troponin if ischemia suspected
• Drug levels: If on antiarrhythmic therapy

Expected Findings by Condition

Arrhythmogenic cardiomyopathy 2:

• ECG: T-wave inversions V1-V3, epsilon waves, prolonged terminal activation duration
• Echo/MRI: RV dilation, reduced RV-EF, wall motion abnormalities, fatty/fibrous replacement

Long QT syndrome 2:

• QTc >500ms or increment >60ms from baseline indicates high TdP risk

Ischemic heart disease 2:

• Q waves, ST-T changes, regional wall motion abnormalities

Empiric Treatment

Acute Management

Hemodynamically unstable arrhythmias:

• Immediate cardioversion/defibrillation
• Advanced cardiac life support protocols 2

Stable wide complex tachycardia 2:

• Obtain 12-lead ECG during tachycardia
• IV antiarrhythmics (amiodarone, procainamide) if VT confirmed
• Avoid AV nodal blockers if uncertain diagnosis

Chronic Management

Antiarrhythmic drugs 5:

• Flecainide: Class IC agent for supraventricular arrhythmias and PVCs
  • Proarrhythmic risk 4% in supraventricular arrhythmias, 13-26% in sustained VT 5
  • Contraindicated in structural heart disease (especially post-MI)
  • Initiate at 200mg/day with slow titration, maximum 300mg/day 5
  • Monitor ECG at steady-state (1-2 weeks) 2
  • Discontinue if QTc >500ms or increment >60ms 2

Risk factor optimization 2:

• Correct electrolyte disturbances (especially hypokalemia from diuretics)
• Review and discontinue QT-prolonging medications when possible
• Optimize heart failure management

Indications to Refer

Immediate Cardiology Referral 2

• Arrhythmic syncope characteristics (supine position, during/after exercise, no prodrome, repetitive) 2
• Structural heart disease with arrhythmias 2
• QT prolongation (QTc >500ms or increment >60ms) 2
• Cardiac symptoms (chest pain, dyspnea) with arrhythmias 2
• Sustained ventricular tachycardia (requires hospital initiation of therapy) 5

Specialized Referral 2

• Children/young adults with arrhythmic syncope: Cardiology specialist assessment including ECG, echocardiogram, exercise test 2
• Family members of sudden cardiac death victims: Systematic evaluation in specialized clinic 2
• Suspected inherited arrhythmic syndromes: Genetic testing and family screening 2

Electrophysiology Referral 2

• Recurrent symptomatic arrhythmias despite medical therapy
• Ablation candidacy assessment
• ICD consideration for high-risk patients

Critical Pitfalls

Diagnostic Pitfalls

• Failing to obtain 12-lead ECG during tachycardia in stable wide complex tachycardia—this is essential for diagnosis 2
• Missing arrhythmic syncope red flags (supine position, exercise-related, no prodrome)—these require immediate cardiology evaluation 2
• Inadequate monitoring duration: Using 24-hour Holter for infrequent symptoms instead of event/implantable recorders 2
• Not correlating symptoms with ECG findings: Arrhythmia detection without symptom correlation has limited clinical utility 2

Risk Assessment Pitfalls

• Underestimating proarrhythmic risk of antiarrhythmics in structural heart disease—flecainide has 13-26% proarrhythmic rate in sustained VT 5
• Initiating Class IC agents outpatient in sustained VT—requires hospital initiation with monitoring 5
• Ignoring left atrial size: LA diameter >48mm strongly predicts arrhythmias and requires close monitoring 4
• Missing drug interactions: CYP inhibitors, QT-prolonging drugs, potassium-wasting diuretics increase arrhythmic risk 2

Management Pitfalls

• Rapid dose escalation of antiarrhythmics—increases proarrhythmic events; slow titration essential 5
• Failure to recheck ECG at steady-state (1-2 weeks) after initiating Class B/B* drugs 2
• Not discontinuing therapy when QTc >500ms or increases >60ms from baseline 2
• Outpatient monitoring when suspicion is high: Prompt diagnosis and prevention warranted, not outpatient ambulatory monitoring 2

Follow-up Pitfalls

• Inadequate serial imaging in progressive cardiomyopathies (arrhythmogenic cardiomyopathy requires annual echo, CMR every 3-5 years) 2
• Missing family screening in inherited conditions—first-degree relatives require systematic evaluation 2
• Accepting "normal" QTc in high-risk patients: Considerable overlap exists between healthy individuals and long QT carriers 2