From the Guidelines
Sinus tachycardia with an irregular rate is most commonly caused by physiological or pathological conditions that increase the heart rate, such as infection, dehydration, anemia, heart failure, hyperthyroidism, or the use of exogenous substances like caffeine or beta-agonist drugs, as stated in the 2016 ACC/AHA/HRS guideline 1.
Causes of Sinus Tachycardia with Irregular Rate
The causes can be broadly categorized into:
- Physiological conditions like sinus arrhythmia, where the heart rate increases during inspiration and decreases during expiration
- Pathological conditions such as premature atrial or ventricular contractions, atrial fibrillation with rapid ventricular response, or the effects of certain medications
- Other factors including anxiety, fever, hyperthyroidism, anemia, dehydration, pain, or heart failure
Evaluation and Management
Evaluation typically involves an ECG to distinguish between the different causes, as treatment depends on the underlying mechanism.
- Management focuses on addressing the root cause rather than just treating the fast heart rate, as emphasized in the 2003 ACC/AHA/ESC guidelines 1.
- If symptoms like dizziness, chest pain, or shortness of breath occur with the irregular tachycardia, immediate medical attention is necessary to prevent potential morbidity and mortality. Some key points to consider in management include:
- Identifying and treating the underlying cause
- The potential use of beta blockers for symptomatic relief in certain cases, such as physiological symptomatic sinus tachycardia triggered by emotional stress or anxiety-related disorders
- The role of nondihydropyridine calcium-channel blockers in patients with symptomatic thyrotoxicosis when beta blockade is contraindicated
From the Research
Causes of Sinus Tachycardia with Irregular Rate
- Sinus tachycardia (ST) can be caused by various factors, including medical conditions such as pulmonary embolism, anemia, infection, or hyperthyroidism 2
- In some cases, ST may not have an easily explainable cause, but can be associated with serious underlying pathology and intolerable symptoms 2
- Inappropriate sinus tachycardia (IST) is a clinical syndrome characterized by fast sinus rates (>100 b.p.m. at rest or >90 b.p.m. on average over 24 h) associated with symptoms such as palpitations, chest pain, fatigue, shortness of breath, presyncope, and syncope 3, 4
- Possible mechanisms of IST include intrinsic sinus node abnormality, beta-adrenergic receptor stimulating autoantibody, beta-adrenergic receptor supersensitivity, muscarinic receptor autoantibody, or hyposensitivity, impaired baroreflex control, depressed efferent parasympathetic/vagal function, nociceptive stimulation, central autonomic overactivity, and aberrant neurohumoral modulation 3
Classification and Diagnosis
- ST can be classified as secondary to a specific, usually treatable, medical condition or be related to several incompletely defined conditions (eg, inappropriate ST, postural tachycardia syndrome, mast cell disorder, or post-COVID syndrome) 2
- A thorough evaluation of secondary causes of tachycardia is required in the work-up of all cases, and if found, must be treated before a diagnosis of IST can be made 4
Treatment Options
- Various treatment options for patients with IST are available, including ivabradine, beta-adrenergic blockers, calcium channel blockers, psychiatric evaluation, and exercise training 3
- Endocardial radiofrequency ablation targeting the sinus node has been used as a treatment modality for otherwise treatment-refractory IST, but the results have been dismal 3