Causes of Intermittent Tachycardia
Intermittent tachycardia is primarily caused by paroxysmal supraventricular arrhythmias (particularly AVNRT and AVRT), atrial fibrillation, atrial flutter, and less commonly by ventricular tachycardia, with the specific etiology determined by whether the rhythm is regular or irregular, narrow or wide complex, and associated with structural heart disease or reversible triggers. 1, 2
Primary Cardiac Mechanisms
Supraventricular Causes (Most Common)
Re-entrant tachycardias account for the majority of intermittent tachycardia episodes:
- AVNRT (AV Nodal Reentrant Tachycardia) involves a re-entry circuit within the AV node using dual pathways, presenting with sudden onset and termination, and is the most common cause of paroxysmal regular tachycardia 1, 2
- AVRT (AV Reciprocating Tachycardia) utilizes an accessory pathway between atria and ventricles, seen in Wolff-Parkinson-White syndrome, and carries risk of sudden death if atrial fibrillation develops 1, 2
- Atrial tachycardia arises from focal automaticity, triggered activity, or micro-reentry within atrial tissue, characterized by discrete P waves with isoelectric segments between them 1, 2
- Atrial flutter represents macro-reentrant circuits typically around the tricuspid annulus, producing characteristic "sawtooth" flutter waves at approximately 300 bpm 1, 2
Atrial fibrillation causes irregular intermittent tachycardia with uncoordinated atrial activation, absent P waves, and irregular R-R intervals, often triggered by drugs, alcohol, surgery, or metabolic disturbances 1
Ventricular Causes
- Ventricular tachycardia produces wide QRS complex tachycardia (>120 milliseconds), most commonly associated with ischemic heart disease, cardiomyopathy, or structural heart disease 1, 3
- Bundle branch reentrant tachycardia represents a specialized form requiring electrophysiologic study for definitive diagnosis 1
Reversible and Secondary Causes
Physiologic and Extrinsic Triggers
Sinus tachycardia accelerates and decelerates gradually (unlike paroxysmal SVT) and requires evaluation for underlying stressors 1:
- Infection, fever, sepsis
- Volume depletion, anemia, hypoxemia
- Hyperthyroidism and metabolic disorders 1, 4
- Anxiety, pain, or emotional stress 1
Drug-Induced Tachycardia
Medications can directly cause or exacerbate tachyarrhythmias 1:
- Cardiovascular drugs (antiarrhythmics paradoxically causing proarrhythmia)
- Stimulants (caffeine, amphetamines, cocaine)
- Anticancer drugs
- Bronchodilators and decongestants
- Adverse drug effects account for 21% of emergency department presentations for compromising bradycardia, but also contribute significantly to tachyarrhythmias 1
Acute Precipitating Events
Temporary reversible causes that must be excluded before attributing tachycardia to intrinsic cardiac disease 1, 2:
- Major surgery (particularly cardiac or thoracic)
- Acute myocardial infarction (14% of compromising arrhythmias) 1
- Pneumonia and acute pulmonary disease
- Electrolyte disorders (hypokalemia, hypomagnesemia) - responsible for 4% of arrhythmias 1
- Pericarditis, myocarditis
- Pulmonary embolism 1
Structural and Chronic Conditions
Cardiac Structural Disease
Underlying heart disease predisposes to intermittent tachycardia and modifies prognosis 2, 5:
- Heart failure (both cause and consequence of persistent tachycardia)
- Hypertension with left atrial enlargement
- Coronary artery disease
- Valvular heart disease (particularly mitral valve disease)
- Cardiomyopathies (hypertrophic, dilated, arrhythmogenic right ventricular)
- Congenital heart disease (Ebstein anomaly, tetralogy of Fallot, atrial septal defects) 2
Chronic Medical Conditions
- Chronic obstructive pulmonary disease (associated with multifocal atrial tachycardia) 1
- Obstructive sleep apnea 1
- Chronic kidney disease 1
- Diabetes mellitus 1
- Obesity 1
Special Diagnostic Considerations
Distinguishing Intermittent from Persistent Bradycardia
The meaning of intermittent bradycardia versus tachycardia requires careful distinction, as intermittent rhythms result from variable contributions of intrinsic cardiac mechanisms and extrinsic reflexes 1. The same principle applies to tachycardia - distinguishing primary cardiac arrhythmia from appropriate physiologic response is essential 1.
Critical Pitfall: Bradycardia-Tachycardia Syndrome
Sinus node dysfunction can manifest as alternating bradycardia and tachycardia episodes, previously called sick sinus syndrome, causing various rhythm disturbances including bradycardia-tachycardia syndrome 4. This represents intrinsic sinus node disease rather than isolated tachycardia 1.
Age-Related Patterns
- Young patients more commonly have AVNRT, AVRT, or accessory pathway-mediated tachycardias, often experiencing very rapid rates that can cause syncope 5
- Older patients (≥65 years) have higher likelihood of atrial fibrillation, atrial flutter, and underlying structural heart disease, with greater propensity for syncope regardless of heart rate 5
Diagnostic Algorithm
ECG documentation during tachycardia is essential for diagnosis 1:
Regular vs irregular rhythm: Regular suggests AVNRT, AVRT, atrial tachycardia, or ventricular tachycardia; irregular suggests atrial fibrillation, multifocal atrial tachycardia, or frequent premature beats 1
QRS width: Narrow (<120 ms) indicates supraventricular origin; wide (>120 ms) suggests ventricular tachycardia or SVT with aberrancy 1
P wave relationship: PR shorter than RP suggests atrial tachycardia; absence of P waves suggests atrial fibrillation; retrograde P waves suggest AVNRT or AVRT 1
Onset/termination pattern: Abrupt onset and termination indicates re-entrant mechanism (AVNRT, AVRT); gradual acceleration suggests sinus tachycardia 1
When ECG documentation is unavailable, prolonged monitoring with Holter monitor, event recorder, or implantable loop recorder is warranted to capture intermittent episodes 1. Electrophysiologic study is reserved for patients with frequent or poorly tolerated episodes requiring definitive diagnosis for treatment planning 1.