In a dehydrated patient with nausea and vomiting who has an electrocardiogram showing sinus tachycardia at 104 bpm, a rightward axis and possible right‑ventricular hypertrophy but no ST‑segment elevation, what is the most likely cause and what is the appropriate initial management?

Sinus Tachycardia in a Dehydrated Patient with Possible RVH

Most Likely Cause

The sinus tachycardia at 104 bpm is most likely a physiological response to dehydration from nausea and vomiting, while the rightward axis and possible RVH findings are borderline and require verification of lead placement before attributing them to true cardiac pathology. 1

Understanding the Sinus Tachycardia

• Sinus tachycardia is defined as a sinus rate exceeding 100 bpm that appropriately responds to physiological stress, including hypovolemia from dehydration. 1

• In this clinical context, the tachycardia represents an appropriate compensatory mechanism to maintain cardiac output in the setting of volume depletion from gastrointestinal losses. 1

• The rate of 104 bpm is modest and consistent with physiological sinus tachycardia rather than a primary cardiac arrhythmia. 2

Evaluating the Rightward Axis and Possible RVH

First: Rule Out Technical Error

Before attributing the rightward axis and RVH pattern to true cardiac pathology, you must verify correct precordial lead placement, as electrode misplacement is the most common cause of apparent ECG abnormalities. 3, 4

• Lead placement variability of as little as 2 cm can create important diagnostic errors, particularly regarding ventricular hypertrophy patterns. 3, 4

• Superior misplacement of V1 and V2 electrodes can reduce R-wave amplitude by approximately 0.1 mV per interspace, creating artifactual patterns. 4

Second: Consider the Clinical Context

Right axis deviation and RVH patterns in the absence of structural heart disease, pulmonary disease, or congenital heart disease are often normal variants, especially in younger patients. 1

• The American Heart Association emphasizes that right axis deviation and prominent anterior forces occur for various reasons other than true RVH, including normal variants. 1

• Ancillary clinical information plays a greater role in recognizing true RVH than it does for left ventricular hypertrophy. 1

Third: Look for Associated Findings

True RVH requires both right axis deviation AND prominent anterior forces in right precordial leads in nearly all cases. 1

• Isolated right axis deviation without other supporting criteria has low specificity for RVH. 1, 5

• The ECG is relatively insensitive for detecting RVH, though some criteria have high specificity. 5

• Associated findings that support true RVH include: tall R waves in V1, deep S waves in V6, and signs of right atrial abnormality (tall peaked P waves >2.5 mm in lead II). 1, 6

Appropriate Initial Management

Immediate Management

Initiate intravenous fluid resuscitation with isotonic crystalloid to correct the hypovolemia causing the sinus tachycardia. 1

• The sinus tachycardia should resolve as volume status normalizes, confirming its physiological nature. 1, 2

• Monitor heart rate response to fluid administration; persistent tachycardia despite adequate hydration warrants investigation for other causes. 2

ECG Follow-Up

Repeat the ECG after rehydration with careful attention to proper lead placement to determine if the rightward axis and RVH pattern persist. 3, 4

• If the ECG normalizes after rehydration and with proper lead placement, no further cardiac workup is needed. 3

• If rightward axis and RVH pattern persist on repeat ECG with confirmed proper lead placement, consider the following differential:

  • Chronic lung disease (look for low voltage in limb leads, persistent S waves in all precordial leads, low R-wave amplitude in V6, and rightward P-wave axis >60 degrees). 1

  • Congenital heart disease (obtain history of known cardiac defects; ECG has greatest accuracy for RVH in this population). 1, 5, 7

  • Pulmonary hypertension (assess for dyspnea, examine for signs of right heart failure, consider echocardiography). 6

  • Normal variant (most likely in young, asymptomatic patients without cardiac risk factors or pulmonary disease). 1

When to Pursue Further Cardiac Evaluation

Obtain echocardiography if the patient has any of the following: 1, 4

• Symptoms of dyspnea, chest pain, or syncope. 4

• Clinical signs of right heart failure or pulmonary hypertension. 6

• Known chronic lung disease with signs of cor pulmonale. 4

• Persistent RVH pattern on repeat ECG with proper lead placement AND clinical suspicion of underlying cardiac or pulmonary pathology. 1, 5

Critical Pitfall to Avoid

Do not pursue extensive cardiac workup for borderline ECG findings in the setting of an obvious physiological stressor (dehydration) without first correcting the underlying cause and repeating the ECG with verified proper lead placement. 3, 4 The combination of modest sinus tachycardia with volume depletion and borderline ECG findings that could easily represent technical error or normal variant does not warrant immediate advanced cardiac testing in an otherwise asymptomatic patient. 1