Differentials
Sinus tachycardia
SIGNS / SYMPTOMS
This arrhythmia is usually compensatory for a reduced stroke volume because of heart failure or volume depletion, or because of sympathetic stimulation from pain, fear, or exogenous catecholamines.
The presence of a clinical disease state plus variation in the atrial rate will usually differentiate this arrhythmia from atrial tachycardia.
INVESTIGATIONS
Vagal maneuvers/adenosine will cause sinus tachycardia to transiently slow down, with slowing of the sinus rate and prolongation of the PR interval before AV block (if it occurs).
AV node re-entrant tachycardia
SIGNS / SYMPTOMS
This supraventricular tachycardia shares some of the causes of focal atrial tachycardia (focal AT). Hence, the two may be indistinguishable based on history and physical exam.
On vagal maneuvers or administering adenosine, in contrast with focal AT, AV node re-entrant tachycardia will abruptly cease. After a pause, sinus rhythm will resume.
INVESTIGATIONS
The 12-lead ECG may show P waves, which can be differentiated from the P waves of atrial tachycardia by the shortened RP interval created by retrograde activation of the atria.
The P waves in atrial tachycardia are found in the second half of the tachycardia cycle (long RP/short PR intervals).
AV re-entrant tachycardia or accessory pathway mediated tachycardia
SIGNS / SYMPTOMS
Difficult to distinguish from focal AT. Vagal maneuvers or adenosine may terminate this tachycardia in contrast with focal AT.
INVESTIGATIONS
The 12-lead ECG may show retrograde P waves (inverted in leads II, III and AVF) in the mid part of the tachycardia cycle (mid-RP intervals). Sinus rhythm ECG may show presence of pre-excitation (Delta wave).
The P waves in atrial tachycardia are found in the second half of the tachycardia cycle (long RP/short PR intervals).
Atrial flutter
SIGNS / SYMPTOMS
This supraventricular tachycardia shares many of the causes of focal AT. Hence, the two may be indistinguishable based on history and physical exam.
Vagal maneuvers/adenosine will transiently slow the ventricular response rate with AV block. The characteristic flutter waves will be revealed and will be unaffected.
INVESTIGATIONS
The 12-lead ECG will show a regular tachycardia with the ventricular response rate being a multiple of the atrial flutter rate (usually 300 bpm).
Unmedicated flutter will usually present in 2:1 AV block with the ventricular response being 148-150 bpm.
The flutter waves will typically distort the baseline, particularly in leads II, III, and AVF for typical right sided counterclockwise atrial flutter.
When AV block is induced in atrial tachycardia, there is an isoelectric interval between P waves, which is not seen in atrial flutter.
Postural orthostatic tachycardia syndrome
SIGNS / SYMPTOMS
Symptoms of orthostatic intolerance (palpitations, lightheadedness, blurred vision, presyncope and syncope, tremor, generalized weakness, fatigue) and an increase in heart rate on standing.
Nonorthostatic symptoms may include dyspnea, gastrointestinal symptoms (bloating, nausea, diarrhea, constipation and abdominal pain), headache, sleep disturbance, cognitive impairment, chest pain, and bladder disturbance.
The patient may also have signs and symptoms of associated comorbidities, such as those of Ehlers-Danlos syndrome and autoimmune diseases, particularly Hashimoto’s thyroiditis and celiac disease.
INVESTIGATIONS
10-minute standing test: patient’s heart rate will typically increase by ≥30 bpm (≥40 bpm in patients ages 12-19 years old) after changing position from supine to standing, and no orthostatic hypotension (sustained drop in systolic blood pressure by ≥20 mmHg).
24-hour Holter monitor: can help confirm the diagnosis by demonstrating the association between tachycardia and orthostatic changes.
Tilt-table test: may be used if the diagnosis is unclear following initial assessment or if the patient is not able to perform a 10-minute standing test. A positive test demonstrates orthostatic tachycardia with changing position. ECG will show P waves similar to sinus rhythm or sinus tachycardia.
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