Cardiology

Background 

Electrical alternans is a beat-to-beat variation in the amplitude or axis of QRS complexes, and occasionally P and T waves, on electrocardiography (ECG). It is most commonly associated with pericardial effusion and cardiac tamponade but may also be seen in other settings such as supraventricular tachycardias or severe left ventricular dysfunction. The phenomenon reflects changes in cardiac electrical axis due to mechanical or electrical shifts of the heart within the thoracic cavity. 

II) Classification/Types 

By ECG Component Affected: 

• QRS Alternans: Most common and clinically relevant; alternating QRS amplitude or axis. 

• T-wave Alternans: May be subtle; associated with repolarization abnormalities and risk of arrhythmias. 

• P-wave Alternans: Less common; typically seen with atrial enlargement or pericardial disease. 

By Mechanism: 

• Mechanical Alternans: Due to swinging of the heart within a fluid-filled pericardial sac (e.g., tamponade). 

• Electrical Alternans: Due to alternation in conduction pathways or repolarization instability. 

Pathophysiology 

Electrical alternans results from mechanical or electrophysiological changes that cause beat-to-beat alternation in cardiac electrical activity. In pericardial tamponade, the heart “swings” within a large pericardial effusion, shifting the heart’s orientation relative to ECG leads. In T-wave alternans, cellular-level alternation in myocardial repolarization creates electrical instability, predisposing to ventricular arrhythmias. 

Epidemiology 

• Most commonly associated with large pericardial effusions and cardiac tamponade. 

• T-wave alternans is seen in patients at high risk for sudden cardiac death (e.g., post-MI, cardiomyopathy). 

• Occurs across all age groups, depending on underlying etiology. 

• Incidence increases in hospitalized patients with advanced cardiac disease. 

Etiology 

I) Causes 

• Pericardial Effusion and Tamponade (most common) 

• Supraventricular tachycardia (especially narrow-complex tachycardias) 

• Advanced heart failure 

• Acute myocardial infarction 

• Electrolyte abnormalities (e.g., hypokalemia, hypocalcemia) 

• Drug toxicity (e.g., digoxin, antiarrhythmics) 

• Cardiomyopathies 

• Congenital long QT syndrome (in T-wave alternans) 

II) Risk Factors 

• Known pericardial disease or pericarditis 

• Renal failure (increased risk for pericardial effusion) 

• Advanced heart failure or cardiomyopathy 

• Recent cardiac surgery or trauma 

• Electrolyte imbalance or drug toxicity 

• History of ventricular arrhythmias 

Clinical Presentation 

I) History (Symptoms) 

• May be asymptomatic if incidental 

• In pericardial tamponade: 

• Dyspnea 

• Chest discomfort or fullness 

• Lightheadedness or syncope 

• Fatigue 

• In arrhythmogenic causes: 

• Palpitations 

• Sudden cardiac arrest (in T-wave alternans) 

II) Physical Exam (Signs) 

• Signs of pericardial tamponade: 

• Hypotension 

• Elevated jugular venous pressure 

• Muffled heart sounds (Beck’s triad) 

• Pulsus paradoxus 

• Tachycardia 

• Weak peripheral pulses 

Differential Diagnosis (DDx) 

• Cardiac tamponade 

• Large pericardial effusion without tamponade 

• Supraventricular tachycardia with aberrancy 

• T-wave alternans in ventricular instability 

• Electrical artifact 

• Low voltage QRS from obesity, COPD, or hypothyroidism 

Diagnostic Tests 

Initial Work-Up 

• 12-lead ECG: Alternating QRS amplitude or axis is diagnostic 

• Echocardiography: Gold standard for detecting pericardial effusion or tamponade 

• Chest X-ray: May show an enlarged, globular cardiac silhouette 

• Cardiac enzymes: Rule out MI if chest pain or ischemic symptoms 

• Electrolytes and renal function: Assess for metabolic contributors 

• Thyroid function: In patients with low voltage and pericardial effusion 

Advanced Testing 

• Cardiac MRI: For detailed pericardial and myocardial assessment 

• T-wave alternans testing (microvolt TWA): Noninvasive risk stratification for sudden cardiac death 

• Electrophysiology study: If underlying arrhythmia is suspected 

Treatment 

I) Acute Management 

If due to cardiac tamponade: 

• Pericardiocentesis: Emergent drainage of pericardial fluid 

• IV fluids to temporarily augment preload 

• Avoid positive pressure ventilation unless intubation is essential 

If due to arrhythmia: 

• Treat underlying rhythm (e.g., vagal maneuvers or adenosine for SVT) 

• Correct electrolyte abnormalities 

• Address ischemia if present 

II) Chronic Management 

• Manage underlying etiology (e.g., treat renal failure, hypothyroidism) 

• Monitor for recurrence of pericardial effusion 

• Implantable cardioverter-defibrillator (ICD) if high-risk T-wave alternans 

• Antiarrhythmic drugs if arrhythmia persists or recurs 

Medications 

Device Therapy 

• Pericardiocentesis catheter: For acute drainage 

• Implantable Cardioverter-Defibrillator (ICD): For high-risk patients with sustained T-wave alternans 

• Pacemaker: If alternans associated with bradyarrhythmia and pauses 

Patient Education, Screening, Vaccines 

Education 

• Report symptoms like dyspnea, chest fullness, or palpitations 

• Understand signs of tamponade: dizziness, low BP, syncope 

• Compliance with follow-up imaging and medication 

Screening/Prevention 

• Periodic echocardiography in patients with known pericardial disease 

• ECG screening in high-risk patients (heart failure, ischemic disease) 

• Monitor drug levels in patients on digoxin, antiarrhythmics 

Vaccinations 

• Pneumococcal and influenza vaccines in heart failure or CKD patients 

Consults/Referrals 

• Cardiology: For diagnostic confirmation, pericardiocentesis, ICD evaluation 

• Electrophysiology: If arrhythmia suspected or for TWA testing 

• Nephrology: For uremic effusion 

• Rheumatology: For autoimmune pericardial disease 

Follow-Up 

Short-Term 

• Monitor for recurrence of effusion via echocardiography 

• Assess for hemodynamic stability post-pericardiocentesis 

• Monitor renal, thyroid, and electrolyte status 

Long-Term 

• Ongoing cardiology follow-up 

• ICD checks if implanted 

• Echocardiographic surveillance of pericardium if high risk 

Prognosis 

• Excellent with prompt drainage in pericardial tamponade 

• Poor if electrical alternans is a marker of impending cardiac arrest 

• T-wave alternans may predict sudden cardiac death in high-risk patients 

• Recurrence risk depends on underlying etiology (e.g., autoimmune, uremia)