Supraventricular Tachycardia (SVT)

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Technically Supraventricular Tachycardia (SVT) is a broad term that covers both atrial tachydysrhythmias (such as atrial flutter and atrial fibrillation) and atrioventricular tachydysrhythmias.  However, in common practice most healthcare providers use the term Supraventricular Tachycardia or SVT to refer specifically to arrhythmias that are atrioventricular tachydysrhythmias.  These arrhythmias arise from an abnormal electrical impulse produce by or dependent on the AV node.

Types of Atrioventricular tachydysrhythmias

• AV nodal re-entrant tachycardia (AVNRT) (most common form, >50%); involves a reentrant circuit in the AV node itself
• AV re-entrant tachycardia (AVRT); involves a reentrant circuit formed by aberrant myocardial accessory pathways between the atria and ventricles. Conduction may be orthodromic or antedromic down the normal His-Purkinje pathway, the latter tends to produce a wide QRS complex.
• Junctional ectopic tachycardia (rare)
• Non-paroxysmal junctional tachycardia (rare)

Causes of SVT

AVNRT; associated with:

• Myocardial ischemia
• Rheumatoid heart disease
• Mitral valve prolapse
• Medications, poisoning and toxic exposures (e.g. caffeine, theophylline)
• Pericarditis
• Dehydration
• Electrolyte Imbalances

AVRT; associated with:

• Presence of an accessory tract, often with evidence of a pre-excitation syndrome on the baseline ECG (e.g. Lown-Ganong-Levine syndrome)
• Ebstein’s anomaly
• Dehydration
• Electrolyte Imbalances

Junctional ectopic tachycardia and Non-paroxysmal junctional tachycardia

• Cardiac ischemia
• Digoxin toxicity
• Cardiac surgery
• Dehydration
• Electrolyte Imbalances

In all types of SVT symptoms result from the fact that the heart fills during diastole with diastole being approximately 2/3 of the cardiac pumping cycle and the faster the ventricular rate the less time the ventricles have to fill.  If the ventricles don’t fill then the cardiac output drops causing less blood to be pumped to the extremities and less blood to be returned to the heard to feed oxygenated blood to the myocardium and be pumped again out to the body.  This drop in cardiac output results in the following symptoms getting worse as the cardiac output continues to drop unless the ventricular rate is slowed.

Symptoms see in stable SVT patients

• SOB
• Fatigue
• Palpitations
• Numbness in Extremities

Symptoms see in Unstable SVT patients

• Chest Pain
• Hypotension
• Loss of Consciousness

Treatment

Consider and treat all underlying causes while providing symptomatic are and support for all stable patients.  Vagal maneuvers and Adenosine may be used to slow stable WVT to make it a better perfusing rhythm or to convert stable SVT patients to a sinus rhythm.  Unstable SVT should always be treated with synchronized cardioversion immediately.  Recommended dose is 50-100 Joules.  Drugs should not be used to treat unstable tachycardia.