Tachycardia is defined as heart rate of more than 100 beats per minute. The heart beats as a result of electrical activity that spread throughout the myocardium (heart muscle). This electrical activity normally originates at sinu-atrial node, a focus in right atrium. Tachycardia occurs as result of increased frequency of electrical discharge from the sinu-atrial node (SA node) or from another focus. When this focus in situated in the atrium, it is called supra-ventricular tachycardia.
Atrial fibrillation, atrial flutter also leads to supraventricular tachycardia. Supraventricular tachycardia can lead to reduced cardiac output and embolisation. When there is tachycardia, the diastolic time reduces. Diastole is the time period where the heart is relaxed. During this period, the atria and ventricles get filled with blood. When there is tachycardia, the amount of blood coming to fill the atria reduces significantly. As a result, the cardiac output reduces. Arrhythmias such as atrial fibrillation creates a turbulent flow. Turbulence results in blood clot formation. These blood clots can shoot in to the systemic circulation and block small blood vessels and give rise to strokes, myocardial infarction etc. Therefore, it is important to treat supraventricular tachycardia.
Medical treatment of supreventricular tachycardia includes several drugs and manures. They can be remembered by the mnemonic ABCDE.
- A - Adenosin
Adenosin is an alpha 1 receptor blocker. It acts on the atrio-ventricular node (AV node). AV node transmits impulses from atrium to the ventricle. When the drug is given intravenously, it blocks excessive impulses passing to the ventricles. As a result the ventricular rate reduces.
- Beta Blocker
Beta blockers also reduce the heart rate.
- Calcium Channel Blocker
- Digoxin
Digoxin is a cardiac glycoside. It inhibits sodium potasium ATPase pump. As a result the heart rate reduces. It also has a positive inotropic effect (increases myocardial contractility) on the myocardium. Its effect on AV node, prevent excessive impulses passing in to the ventricles.
- Excitation
Excitation includes manueurs used to stimulate vagal activity. These manuers include carotid massage, sprinkling cold water on to the face etc.
Above medications helps to keep the heart rate down and prevent clot formation.
