What Is Arrhythmia?
Normal Cardiac Rhythm
The human heart is a double pump: it receives deoxygenated blood from the venous circulation and oxygenates it by propelling it to the lungs, then receives it again so that oxygenated blood can be sent to the rest of the body.
The effectiveness of this double pumping action depends on the slightly skewed contractions of the right and left atria and right and left ventricles, such that a synchrony of directional flow results in an effective cardiac output. This synchrony depends on a normal electrical pathway that originates with a stimulus in the heart’s “pacemaker,” the sinoatrial (SA) node in the right atrium. From there, the conduction wave of impulses travels right-to-left and superior-to-inferior. With the help of the one-way valve mechanisms between atria and ventricles and between ventricles and the extra-cardiac circulation, a vector force outward is affected without any counterproductive reverse or back-flow.
The electrical axis originates in the SA node, then travels to the atrioventricular junctional area where the atrioventricular (AV) node resides. From there, the impulses travel inferior along the Bundle of His fibers, and then spread out along the Purkinje fibers where they terminate deep within the ventricles.
Anywhere along this electrical pathway the signal can be blocked or altered, creating a departure from the normal electrical activities upon which effective cardiac output depends:
- A block at the AV node will result in altered signals–or no signals–being propagated further, leaving the slower pace making automaticity of the ventricles to fire off as an escape rhythm.
- Extra (“ectopic”) pacemakers in the atrium can compete with the SA node’s normal pace making, creating atrial arrhythmias that can impact conduction through to the ventricles or create ineffective atrial contractions.
- Re-entry (“aberrant”) signals can initiate a circular, wasted circuit that augments or defeats the normal electrical activity.
- Damage to the electrical system due to ischemia or cell death (myocardial infarction) can destroy the normal synchrony needed for effective cardiac output.
- Sympathetic and parasympathetic influences can stimulate or inhibit the pace making properties and automaticity of the normal heart.