What are the differential diagnoses for a patient presenting with headache and tachycardia?

Differential Diagnoses for Heaviness of the Head and Heart Racing

The most critical differentials to consider are cardiac arrhythmias (particularly supraventricular tachycardia and inappropriate sinus tachycardia), postural orthostatic tachycardia syndrome (POTS), and secondary causes of tachycardia including thyrotoxicosis, anemia, and dehydration. 1

Primary Cardiac Arrhythmias

Supraventricular Tachycardia (SVT)

• Inappropriate sinus tachycardia (IST) presents with resting heart rates >100 bpm and uncomfortable sensations such as heart racing, lightheadedness, weakness, and fatigue 1
• IST predominantly affects young females (90%) with mean age of 38 years, and shows average heart rates >90 bpm over 24 hours 2
• Atrioventricular nodal reentrant tachycardia (AVNRT) is the most common form of SVT, typically with P waves hidden within the QRS complex and may present with palpitations and lightheadedness 3
• Atrioventricular reciprocating tachycardia (AVRT) involves an accessory pathway and may show pre-excitation pattern on baseline ECG 3, 2
• Atrial tachycardia has P wave morphology differing from sinus rhythm, with rates typically 100-250 bpm 2

Physiological Sinus Tachycardia

• This represents an appropriate autonomic response but requires exclusion of underlying pathological causes 1

Postural Orthostatic Tachycardia Syndrome (POTS)

POTS is characterized by frequent symptoms occurring with standing (lightheadedness, palpitations, tremulousness, generalized weakness, blurred vision, exercise intolerance, and fatigue) plus an increase in heart rate ≥30 bpm during positional change from supine to standing (or ≥40 bpm in those 12-19 years of age) without orthostatic hypotension. 1

• The standing heart rate is often >120 bpm 1
• Orthostatic headaches are a key distinguishing feature that can help identify POTS patients, along with new-onset motion sickness and dizziness as a headache trigger 4
• POTS must be excluded before diagnosing inappropriate sinus tachycardia 2
• Treatment includes increased fluid and salt intake, elastic compression stockings, and regular exercise 5

Secondary Causes of Tachycardia (Critical to Exclude)

Thyrotoxicosis

• Presents with headache and tachycardia of sudden onset, with low TSH and elevated T4 levels 6
• Can result from exogenous thyroid hormone intake (including inadvertent consumption in meat products) or primary hyperthyroidism 6
• Hyperthyroidism should be systematically excluded as a potential cause of ectopic beats and tachycardia 7

Other Metabolic and Systemic Causes

• Anemia, dehydration, pain, infection with fever, and heart failure all cause physiological sinus tachycardia that resolves with correction of the underlying cause 1
• Electrolyte abnormalities, particularly hypokalemia, should be considered 7
• Anxiety disorders are important triggers and may be associated with IST 1

Medication and Substance-Related

• Exogenous substances including caffeine, beta-agonist drugs (albuterol, salmeterol), and illicit stimulant drugs (amphetamines, cocaine) cause tachycardia 1
• Excessive caffeine, alcohol, nicotine intake, or recreational drugs should be reviewed as precipitating factors 7

Hypertensive Urgency/Emergency

• Severe elevations in blood pressure associated with severe headache represent hypertensive urgency 1
• Hypertensive emergencies require immediate blood pressure reduction in an intensive care setting 1

Neurologic Causes

• COVID-19 infection can present with headache (28% of cases) and arrhythmia (17% of cases), potentially related to cortical venous thrombosis, systemic inflammation, and cytokine storm 8
• Intracranial hypotension or CSF leak should be considered if orthostatic headache is prominent 5

Diagnostic Approach Algorithm

Step 1: Obtain 12-Lead ECG

• Determine QRS width (<120 ms narrow vs ≥120 ms wide) and rhythm regularity 3, 2
• Compare to baseline ECG in sinus rhythm when available 3
• Assess P-wave morphology and relationship to QRS complex 3

Step 2: Assess Hemodynamic Stability

• If hemodynamically unstable, immediate synchronized DC cardioversion is first-line treatment 3
• If stable, proceed with diagnostic evaluation 3

Step 3: Systematic Exclusion of Secondary Causes

• Check thyroid function tests (TSH, free T4) 6
• Complete blood count to exclude anemia 1
• Basic metabolic panel for electrolytes and renal function 7
• Review all medications and substance use history 1, 7
• Assess hydration status 1

Step 4: Orthostatic Vital Signs

• Measure heart rate and blood pressure supine and after 3 minutes of standing 1
• Heart rate increase ≥30 bpm (≥40 bpm if age 12-19) without blood pressure drop >20 mmHg systolic suggests POTS 1

Step 5: Extended Monitoring if Needed

• 24-hour Holter monitoring if episodes occur several times per week 2
• Event recorder or external loop recorder if episodes occur less than weekly but more than monthly 2

Critical Pitfalls to Avoid

• Never administer verapamil or diltiazem for wide-complex tachycardia of uncertain etiology, as it can cause severe hypotension or accelerated ventricular rate 3
• Do not diagnose inappropriate sinus tachycardia without first excluding POTS and all secondary causes 1, 2
• Avoid initiating antiarrhythmic treatment with class I or class III drugs without documented sustained arrhythmia due to proarrhythmia risk 7
• Consider that patients with preexisting headache disorders may develop phenotypically similar headaches when a secondary cause occurs, requiring higher suspicion for underlying pathology 9