An arrhythmia is a disruption in the heart’s normal electrical cycle, resulting in a heartbeat that is too fast, too slow, or irregular. When this rhythm is compromised, the heart may not deliver sufficient oxygenated blood, which can lead to various health complications. For medical professionals, organizing these rhythm disturbances into a clear classification system is necessary to accurately diagnose the problem and select the most effective treatment approach.
The Role of the Electrocardiogram
The primary method for identifying and classifying a heart rhythm disturbance involves the use of an electrocardiogram (ECG or EKG). This non-invasive diagnostic test records the electrical activity generated by the heart muscle as it contracts and relaxes. The electrical signals are picked up by electrodes placed on the skin and translated into a visible tracing, or waveform. By analyzing the shape and spacing of the waveform components, a physician can pinpoint where the electrical impulse originated and how it propagated through the heart chambers. This visual evidence of abnormal electrical pathways provides the necessary data to apply the formal classification criteria.
Fundamental Classification Criteria
The initial step in categorizing any abnormal rhythm relies on two basic parameters: the heart’s rate and its regularity. Heart rate is measured in beats per minute (bpm) and establishes the first major division. A resting heart rate below 60 bpm is classified as bradycardia (a slow rhythm), while a rate exceeding 100 bpm is defined as tachycardia (a fast rhythm). Beyond speed, the regularity of the heartbeats determines the second layer of classification. A regular rhythm features predictable, consistent spacing between heartbeats. An irregular rhythm is unpredictable, with inconsistent intervals between beats that suggest a disorganized electrical source.
Classification by Origin Site
After assessing the rate and rhythm, the classification system organizes arrhythmias based on the anatomical location where the abnormal electrical signal originates. The heart is divided into two major regions for this purpose: above and below the ventricles. Arrhythmias that begin in the atria or the atrioventricular (AV) node are grouped as supraventricular arrhythmias (SVAs), meaning they start above the lower pumping chambers. These rhythms are often less immediately life-threatening because the ventricles may still receive some controlled electrical input. In contrast, ventricular arrhythmias (VAs) originate below the AV node, directly within the muscular walls of the ventricles. These rhythms tend to be more dangerous because the disorganized electrical activity severely impairs the heart’s ability to pump blood effectively.
Major Arrhythmia Examples
The classification criteria of rate, rhythm, and origin are applied to specific clinical conditions. Sinus Bradycardia and Sinus Tachycardia are rate disturbances that originate correctly in the sinus node, the heart’s natural pacemaker, but fire too slowly or too quickly. Sinus Bradycardia is a slow, regular rhythm below 60 bpm, while Sinus Tachycardia is a fast, regular rhythm above 100 bpm, often caused by factors like exercise or stress.
Atrial Fibrillation
Atrial Fibrillation (AFib) is a common supraventricular arrhythmia characterized by chaotic electrical signals originating from multiple sites in the atria, causing the upper chambers to quiver rather than contract effectively. On an ECG, it presents as a rapid and “irregularly irregular” rhythm, often leading to heart rates over 100 bpm.
Ventricular Tachycardia
A more severe condition is Ventricular Tachycardia (VT), which is classified as a ventricular arrhythmia. VT is a fast rhythm (100 to 250 bpm) that originates from an abnormal electrical focus within the ventricles. This rapid, disorganized firing does not allow the ventricles enough time to properly fill with blood, compromising the body’s circulation and requiring immediate medical attention.