Systematic Causes of Palpitations for Exam Preparation
Palpitations can be systematically categorized into cardiac arrhythmic causes, structural cardiac causes, psychiatric causes, systemic non-cardiac causes, and medication/substance-induced causes, with cardiac arrhythmias and anxiety being the most common etiologies.
Classification by Clinical Presentation
Palpitations can be divided into four clinical groups based on how patients describe them 1:
- Extrasystolic: Described as pauses or skipped beats followed by a strong heartbeat, typically caused by premature atrial or ventricular contractions 2
- Tachycardic: Regular, rapid palpitations with sudden onset and termination (paroxysmal), suggesting re-entrant tachycardias like AVNRT or AVRT 2
- Anxiety-related: Associated with panic disorder symptoms, which fulfill criteria for panic disorder in 67% of patients with unrecognized SVT 2
- Intense: Perception of forceful heartbeats without necessarily increased rate 1
Etiological Classification
1. Cardiac Arrhythmic Causes (Most Important for Morbidity/Mortality)
Atrial Arrhythmias 2:
- Atrial premature complexes (conducted and nonconducted) - benign but common 2
- Atrial fibrillation - irregular rhythm from numerous atrial impulses conducted irregularly through AV node 3, 4
- Atrial flutter (typical and atypical forms) 2
- Atrial tachycardia (ectopic, with or without AV block) 2
- Multifocal atrial tachycardia - characterized by irregular P waves with at least three different morphologies, most common in pulmonary disease patients 2, 3
Junctional (AV Nodal) Arrhythmias 2:
- AVNRT (atrioventricular nodal re-entrant tachycardia) - more common in women, mean onset age 32±18 years 2
- AVRT (atrioventricular re-entrant tachycardia) - involves accessory pathway, mean onset age 23±14 years 2
- Premature junctional complexes 2
- Nonparoxysmal junctional tachycardia 2
Ventricular Arrhythmias 2:
- Ventricular premature complexes (VPCs/PVCs) 2
- Ventricular tachycardia - monomorphic, polymorphic, sustained, nonsustained, torsades de pointes 2
- Accelerated idioventricular rhythm - rate 60-100 bpm 3
- Ventricular flutter and fibrillation 2
Pre-excitation Syndromes 2:
- Wolff-Parkinson-White syndrome - manifest pre-excitation occurs in 0.1-0.3% of general population; 64% symptomatic at presentation 2, 5
Conduction Abnormalities 2:
- Complete left bundle branch block - QRS >0.12 seconds with QS/rS in V1, broad notched R in I and V6 3, 4
- Complete right bundle branch block - QRS >0.12 seconds with rSR' in V1, wide slurred S in I and V6 4
- Third-degree AV block 2
2. Structural Cardiac Causes (Non-Arrhythmic) 1, 6
- Mitral valve prolapse - frequently associated with palpitations 5
- Valvular heart disease (aortic stenosis, other valvular lesions) 2, 5
- Cardiomyopathy (hypertrophic, dilated) 5
- Congestive heart failure 6
- Pericarditis 6
- Coronary artery disease 5
3. Psychiatric Causes (31% of cases) 7
- Panic disorder - criteria fulfilled in 67% of patients with unrecognized SVT 2
- Anxiety disorders - physicians attribute symptoms to anxiety/stress in 54% of patients, more commonly in women 2
- Somatization disorder 7
- Depression 7
4. Systemic Non-Cardiac Causes 1, 6
Endocrine:
Other Systemic:
- Fever/infection - increases sinus tachycardia 2
- Anemia 1
- Hypovolemia 2
- Electrolyte disturbances (hypokalemia, hypomagnesemia) 1
- Vasovagal syncope 6
Hormonal (Women):
- Luteal phase of menstrual cycle 5
- Pregnancy - mechanical stimuli or arrhythmogenic effect; 22% with established SVT report exacerbation during pregnancy 2, 5
- Perimenopausal period - related to increased sympathetic activity, usually benign 5
5. Medications and Substances 1, 6
Stimulants:
Medications:
- Sympathomimetics (decongestants, bronchodilators) 6
- Anticholinergics (diphenhydramine) - sodium channel blocking properties can cause arrhythmias 8
- Certain antihistamines (terfenadine) - QT prolongation and torsades de pointes 8
- Thyroid hormone replacement (excessive doses) 1
- Withdrawal from beta-blockers 1
6. Unknown Etiology (16% of cases) 6, 7
Key Mechanisms to Understand for Exams 2
Enhanced Automaticity:
- Ectopic foci in atria, AV junction, or pulmonary veins with enhanced phase 4 depolarization 2
- If firing rate exceeds sinus node, becomes predominant pacemaker 2
Triggered Activity:
- Associated with repolarization disturbances 2
- Afterdepolarizations reach threshold and trigger early action potentials 2
Re-entry:
- Most common mechanism 2
- Requires unidirectional block in one limb of circuit and slow conduction 2
- Examples: AVNRT, AVRT with accessory pathway 2
Clinical Pitfalls to Avoid
- Don't assume all palpitations are arrhythmic: Only 43% are cardiac in etiology 7
- Don't dismiss psychiatric causes: Account for 31% of cases and often coexist with cardiac causes 7
- Don't overlook medication history: Over-the-counter medications and supplements frequently cause palpitations 6
- Don't forget gender-specific causes: Women have twice the risk of PSVT and hormonal influences are significant 2, 5
- Recognize high-risk features: Palpitations with syncope, near-syncope, or dizziness require urgent evaluation 6