What is sinus tachycardia?

What is Sinus Tachycardia

Sinus tachycardia is a rhythm originating from the sinus node with a heart rate exceeding 100 beats per minute at rest. 1

Definition and Classification

Sinus tachycardia represents a spectrum of conditions that must be distinguished from one another for appropriate management:

Physiologic Sinus Tachycardia

• An appropriate increase in sinus rate in response to exercise, stress, fever, hypovolemia, or other situations that increase sympathetic tone. 1
• This is a normal compensatory mechanism and requires no specific cardiac intervention beyond addressing the underlying trigger. 1

Inappropriate Sinus Tachycardia (IST)

• Defined as sinus heart rate >100 bpm at rest with a mean 24-hour heart rate >90 bpm that is not due to appropriate physiological responses or identifiable primary causes such as hyperthyroidism or anemia. 1
• The European Heart Journal further clarifies that IST originates along the superior aspect of the crista terminalis (in the sinus node region) at rates above the physiological range, but with no relationship to metabolic or physiological demands. 1
• This condition predominantly affects young to middle-aged patients, with a prevalence of approximately 1% in the middle-aged population, mostly females. 2

Key Distinguishing Features

The critical distinction is that sinus tachycardia—whether physiologic or inappropriate—maintains consistent P-wave morphology because all impulses originate from the same sinus node focus. 3

What Sinus Tachycardia Is NOT:

• Not atrial fibrillation: Sinus tachycardia has distinct P waves with regular morphology, whereas atrial fibrillation shows irregular atrial activity with absence of distinct P waves and irregular R-R intervals. 1, 3
• Not multifocal atrial tachycardia: Unlike MAT which has ≥3 distinct P-wave morphologies with irregular rhythm, sinus tachycardia maintains consistent P-wave morphology. 1, 3
• Not sinus node reentry tachycardia: While this has similar P-wave morphology to sinus rhythm, it is characterized by abrupt onset and termination and can be induced/terminated by programmed stimulation. 1
• Not focal atrial tachycardia: This originates from a localized atrial site outside the sinus node region with discrete P waves and typically an isoelectric segment between P waves. 1

Clinical Approach to Evaluation

When encountering sinus tachycardia, the algorithmic approach should be:

Step 1: Identify Secondary Causes

First, systematically exclude all secondary causes of appropriate sinus tachycardia: 4, 5

• Pulmonary embolism
• Anemia
• Infection/sepsis
• Hyperthyroidism
• Hypovolemia/dehydration
• Medications (stimulants, bronchodilators)
• Pain
• Anxiety
• Heart failure
• Hypoxia

Step 2: Consider Specific Syndromes

If no secondary cause is identified, consider: 4, 5

• Postural orthostatic tachycardia syndrome (POTS): A form of dysautonomia identified during head-up tilt table testing. 1
• Post-COVID syndrome: Increasingly recognized as a cause of persistent sinus tachycardia. 4
• Mast cell disorders: Can present with unexplained tachycardia. 4

Step 3: Diagnosis of IST

IST is a diagnosis of exclusion made only after ruling out all secondary causes and specific syndromes. 6, 5

Clinical Significance and Prognosis

For Physiologic Sinus Tachycardia:

• Treatment focuses on addressing the underlying cause. 4
• The tachycardia itself requires no specific cardiac intervention. 4

For Inappropriate Sinus Tachycardia:

• The long-term outcome appears to be benign, with no association with tachycardia-induced cardiomyopathy or increased major cardiovascular events. 6, 2
• However, patients may experience significant symptoms including palpitations, chest pain, fatigue, shortness of breath, presyncope, and syncope that can impair quality of life. 6, 2
• Treatment may be unnecessary if symptoms are tolerable, or may be as simple as physical training. 6

Common Pitfalls to Avoid

• Do not diagnose IST without first excluding all secondary causes: The diagnosis requires systematic evaluation for hyperthyroidism, anemia, pulmonary embolism, medications, and other treatable conditions. 4, 5
• Do not confuse sinus tachycardia with other supraventricular tachycardias: The presence of consistent P-wave morphology distinguishes it from atrial fibrillation, multifocal atrial tachycardia, and focal atrial tachycardia. 1, 3
• Do not overtreat IST: Given its benign prognosis, aggressive intervention should be reserved for patients with intolerable symptoms. 6
• Recognize that elevated resting heart rate within the "normal" range (but approaching 100 bpm) is independently associated with increased cardiovascular mortality risk: This is frequently underappreciated in clinical practice. 7