The heart operates as a precisely coordinated pump, driven by an intricate internal electrical system. A normal heart rhythm, known as a sinus rhythm, begins with an electrical impulse generated by the sinoatrial (SA) node, the heart’s natural pacemaker. This impulse travels in a specific pathway, leading to a regular, coordinated sequence of contractions that effectively move blood through the body. An arrhythmia is a disorder where this organized electrical signaling system malfunctions, causing the heart to beat too quickly, too slowly, or with an irregular pattern.
Grouping Arrhythmias by Rate
Arrhythmias are fundamentally classified by the speed of the heartbeat, measured in beats per minute (BPM). This method divides rhythm disorders into two overarching categories: those that are too slow and those that are too fast. These rate classifications immediately indicate a potential problem with the heart’s ability to maintain adequate blood flow.
Bradycardia is the term for an abnormally slow heart rate, typically defined as fewer than 60 BPM in an adult. While a slow rate can be normal for highly conditioned athletes, a pathologically slow rate is problematic because the heart cannot pump enough blood to meet the body’s metabolic needs. This low output can lead to symptoms like weakness, dizziness, and fainting.
Tachycardia involves an excessively fast heart rate, generally considered to be over 100 BPM at rest. An overly rapid heart rhythm is inefficient because the heart’s chambers do not have enough time to fully fill with blood between beats. The quick, shallow contractions reduce the amount of blood ejected, resulting in insufficient circulation to the body’s organs and tissues.
Grouping Arrhythmias by Origin
Classification by origin pinpoints where the electrical malfunction occurs within the heart’s four chambers. The electrical impulse normally begins in the SA node, moves through the atria (upper chambers), pauses briefly at the atrioventricular (AV) node, and then rapidly spreads through the ventricles (lower chambers). Disruption at any point along this path defines the arrhythmia’s origin.
Supraventricular arrhythmias (SVAs) originate in the tissue above the ventricles, meaning the atria or the AV node. These are often less immediately life-threatening because the ventricles, which pump blood to the body, are usually still able to contract, though sometimes inefficiently. The AV node acts as a protective bottleneck, often preventing fast, erratic atrial signals from fully reaching the ventricles.
Ventricular arrhythmias originate directly in the heart’s lower chambers, the ventricles, or the specialized conduction system within them. Because these chambers are responsible for pushing blood to the lungs and the rest of the body, a malfunction here can severely compromise circulation. Ventricular arrhythmias are considered more serious and carry a higher risk of sudden cardiac arrest because they directly impair the heart’s primary pumping function.
Understanding the Most Common Arrhythmia Types
Applying these classifications to specific conditions provides a clearer understanding of how different arrhythmias affect heart function. Atrial Fibrillation (AFib) is the most common sustained arrhythmia, classified as a Supraventricular Tachycardia. In AFib, electrical signals in the atria are chaotic, causing the upper chambers to quiver or “fibrillate” instead of contracting effectively.
This rapid atrial activity floods the AV node with impulses, resulting in a fast and highly irregular ventricular heart rate, often ranging between 100 and 175 BPM. The primary concern with AFib is not only inefficient heart function but also the risk of blood pooling in the quivering atria, which can lead to the formation of clots and a subsequent stroke.
Ventricular Fibrillation (V-Fib) is a dangerous condition classified as a Ventricular Tachyarrhythmia. The electrical impulses in the ventricles become chaotic, causing the lower chambers to twitch or “quiver” instead of contracting in a synchronized manner. This results in the cessation of effective pumping action, leading to immediate cardiac arrest and requiring immediate defibrillation to restore a viable rhythm.
Premature Ventricular Contractions (PVCs) are a common form of ventricular rhythm disturbance, defined as extra, early heartbeats originating in the ventricles. These are usually isolated events that briefly interrupt the normal rhythm, often perceived as a “skipped” or “fluttering” beat in the chest. PVCs are classified as a Ventricular Arrhythmia and are generally benign, though they can signal underlying issues or increase the risk of more serious ventricular rhythms.
Sick Sinus Syndrome (SSS) is classified as a Bradycardia, relating to dysfunction of the SA node, the heart’s natural pacemaker. In SSS, the SA node fails to generate impulses at a regular rate, leading to persistent sinus bradycardia, or periods of sinus pause where electrical activity stops entirely. A variant, known as bradycardia-tachycardia syndrome, involves alternating episodes of slow heart rates and fast supraventricular tachycardias, complicating diagnosis and management.