Causes of Resting Heart Rate in the Upper 90s
Understanding the Clinical Context
A resting heart rate in the upper 90s (90–99 bpm) falls within the normal adult range and does not constitute tachycardia, which is defined as ≥100 bpm by major cardiology societies. 1 This heart rate is physiologically normal and typically does not require intervention unless accompanied by symptoms or underlying pathology. 1
Common Physiological Causes
The most frequent explanations for a heart rate in the upper 90s include:
Physical deconditioning or recent activity: Even minimal exertion shortly before measurement can elevate resting heart rate into the upper normal range. 1
Emotional stress and anxiety: Normal catecholamine-driven responses to psychological stress commonly produce heart rates in this range. 2, 3
Caffeine and stimulant intake: Coffee, tea, energy drinks, nicotine, and over-the-counter supplements containing stimulants routinely elevate heart rate. 1, 2, 3
Medications: Beta-agonists (albuterol), aminophylline, decongestants, and certain psychiatric medications with anticholinergic properties (e.g., diphenhydramine at 50 mg daily) increase heart rate. 1, 2
Pathological Causes to Exclude
When a heart rate in the upper 90s persists or is accompanied by symptoms, systematically evaluate for:
Hyperthyroidism: Check TSH and free T4 levels, as thyroid dysfunction commonly presents with persistent elevation in heart rate. 1
Anemia: Obtain a complete blood count to assess hemoglobin levels. 1, 2
Dehydration/hypovolemia: Assess volume status clinically and consider a basic metabolic panel. 1, 2
Infection/fever: Evaluate for signs of infection, as fever increases metabolic demands and heart rate. 2, 3
Pain: Inadequate analgesia or unrecognized pain syndromes can sustain elevated heart rates. 2
Anticholinergic medication burden: If taking diphenhydramine 50 mg daily plus chlorpromazine 100 mg daily, the combined anticholinergic effect significantly contributes to tachycardia; reducing diphenhydramine to 25 mg daily can produce clinically meaningful heart rate reduction. 2
Diagnostic Approach
Obtain a 12-lead ECG to confirm sinus rhythm (upright P waves in leads I, II, aVF; negative in aVR) and exclude atrial tachycardia, sinus node reentrant tachycardia, or other supraventricular arrhythmias. 1, 2
Key steps include:
Review all medications and substances: Specifically ask about caffeine intake, beta-agonists, stimulants, amphetamines, cocaine, cannabis, and over-the-counter supplements. 1, 2
Assess for secondary causes: Systematically check thyroid function, hemoglobin, volume status, and signs of infection or pain. 1, 2
Consider autonomic dysfunction: If all secondary causes are excluded and symptoms are present (palpitations, fatigue, lightheadedness), evaluate for inappropriate sinus tachycardia (IST) or postural orthostatic tachycardia syndrome (POTS). 2, 4
When to Intervene
Do not initiate beta-blockers or other rate-controlling medications for asymptomatic heart rates in the upper 90s, as treatment focuses on underlying causes, not the heart rate itself. 1 A heart rate of 90–99 bpm is within normal limits and does not cause hemodynamic instability or symptoms unless the patient has impaired ventricular function. 1
Treatment is indicated only when:
Reversible causes are identified and corrected: Treat hyperthyroidism, anemia, dehydration, infection, or discontinue offending medications. 1, 2
Inappropriate sinus tachycardia is diagnosed: This requires resting heart rate >100 bpm, average 24-hour rate >90 bpm, and debilitating symptoms after excluding all secondary causes. 1, 2 For symptomatic IST, ivabradine is reasonable as first-line therapy (Class IIa recommendation), with beta-blockers as an alternative (Class IIb). 2, 5
Anxiety-related tachycardia is symptomatic: Beta-blockers are first-line for emotional stress-related tachycardia, with cognitive-behavioral therapy demonstrating clear benefit for recurrent symptoms. 2, 3
Important Caveats
Rates <150 bpm are unlikely to cause symptoms or hemodynamic compromise unless underlying ventricular dysfunction exists, indicating the elevated rate is usually a physiologic response. 1
Immediate cardiology referral is mandatory if the ECG shows pre-excitation (WPW syndrome), wide-complex tachycardia of unknown origin, syncope during tachycardia or exercise, or documented sustained supraventricular tachycardia. 1
Avoid extensive cardiac testing in patients with multiple negative evaluations; instead, consider cognitive-behavioral therapy for anxiety-related symptoms. 3