Tachycardias

Tachycardias are rapid heart rhythms defined by a heart rate faster than the normal resting rate. In adults, a resting heart rate above about 100 beats per minute is commonly considered tachycardic. Tachycardia refers to the rate itself; tachyarrhythmia is used when the rapid rate stems from an abnormal electrical rhythm. They can originate from the atria, the atrioventricular (AV) node, or the ventricles and may be benign or a sign of heart disease.

They are broadly classified as supraventricular tachycardias (originating above the ventricles) and ventricular tachycardias (originating in the ventricles). Supraventricular tachycardias include sinus tachycardia, AV nodal reentrant tachycardia, AV reentrant tachycardia (as in WPW), and atrial tachycardias such as atrial flutter or atrial fibrillation with rapid ventricular response. Ventricular tachycardias are usually categorized as monomorphic or polymorphic and are more likely to reflect structural heart disease or acute ischemia.

Causes include physiologic states (exercise, fever, anxiety, anemia), medications or stimulants, electrolyte disturbances, ischemic heart disease, cardiomyopathy, and other cardiac conditions. Some tachycardias are intermittent while others are sustained and can lead to reduced cardiac output or palpitations, and in some cases may cause hemodynamic instability.

Diagnosis relies on clinical assessment and electrocardiography, with continuous monitoring as needed. Management depends on stability and type. Stable SVT may respond to vagal maneuvers, with adenosine or rate-controlling drugs (beta-blockers or calcium channel blockers) as needed. Unstable tachycardias require urgent synchronized cardioversion. VT treatment focuses on antiarrhythmic drugs and/or cardioversion, with attention to underlying causes. Long-term options include catheter ablation for select SVTs and AF/flutter or VT, plus anticoagulation when stroke risk is elevated.