Arrhythmias - Supraventricular tachycardia (SVT): Nursing

Supraventricular tachycardia, or SVT for short, is an arrhythmia where the heart beats faster than normal, meaning over 100 bpm, but most clients with SVT have a heart rate between 151 and 220 bpm. The cause of the tachyarrhythmia must originate from above the ventricles, and this could be from the myocytes of the atrium or part of the heart’s conduction system. The most common type is called paroxysmal SVT, or PST where there’s sporadic attacks that start and stop suddenly.

Now, the cardiac conduction system is made up of specialized myocardial cells that can create and transport electrical potential, also called an action potential. These cells have many special features, including automaticity, meaning that they can generate an impulse, excitability, which is the ability to respond to a stimulus by creating an electrical impulse, conductivity meaning they can carry the impulse to other cells, and contractility, which is the ability to shorten the length of their fibers, causing a contraction.

Alright, now let’s look at the normal electrical conduction pathway in the heart on an ECG, which shows how the depolarization wave flows through the heart during each heartbeat. The normal electrical activity of the heart starts in the sinoatrial or SA node, which is considered the pacemaker of the heart. Then, the impulse is conducted through the atria, causing depolarization and creating the P wave on an ECG. When the atrial muscle cells get depolarized, they contract, pushing blood from the atria into the ventricles. From the atria, the impulse goes to the atrioventricular, or AV node, where the impulse propagation speed slows way down. The interval from the atrial depolarization to just before ventricular depolarization is the PR interval on an ECG. This delay allows the atria to contract while the ventricles fill with blood. From the AV node, the impulse goes through the Bundle of His, then to the right and left bundle branches, and finally through the Purkinje fibers, which deliver the impulse to the right and left ventricles, causing them to depolarize, and is represented by the QRS complex on an ECG.