The human heart normally beats in a regular pattern, known as normal sinus rhythm, orchestrated by the sinoatrial (SA) node. This natural pacemaker in the upper right chamber generates electrical impulses that spread, causing heart chambers to contract and pump blood. A typical resting heart rate is 60 to 100 beats per minute (bpm).
An arrhythmia is any deviation from this standard rhythm. It can manifest as the heart beating too rapidly (tachycardia), too slowly (bradycardia), or irregularly.
Supraventricular Arrhythmias
Supraventricular arrhythmias originate in the heart’s upper chambers (atria) or the atrioventricular (AV) node, a gateway to the lower chambers. These rhythms can cause the heart to beat either too quickly or too slowly, impacting its ability to pump blood effectively. While often less dangerous than those from the lower chambers, some supraventricular arrhythmias can lead to serious complications like stroke or heart failure.
Atrial Fibrillation (AFib)
Atrial fibrillation is the most common arrhythmia, characterized by chaotic electrical activity in the atria. Instead of coordinated contractions, the atria quiver ineffectively, preventing proper blood flow into the ventricles. This chaotic electrical signaling can lead to a rapid and irregular ventricular heartbeat, often exceeding 100 beats per minute. Left untreated, AFib can increase the risk of blood clot formation and subsequent stroke.
Atrial Flutter
Atrial flutter involves an organized, fast electrical circuit in the right atrium. This re-entrant electrical pattern creates a rapid succession of atrial contractions, often appearing as a “sawtooth” pattern on an electrocardiogram. Atrial rates can range from 250 to 350 beats per minute, with the AV node often blocking some impulses, resulting in a regular but fast ventricular response, such as 125-175 bpm in a 2:1 block. Atrial flutter shares similarities with AFib and can sometimes progress into it.
Paroxysmal Supraventricular Tachycardia (PSVT)
Paroxysmal supraventricular tachycardia (PSVT) is a rapid, regular heart rhythm that starts and stops suddenly. This type of arrhythmia involves an abnormal electrical pathway or a re-entrant circuit, within or involving the AV node. Heart rates during PSVT episodes range from 150 to 250 beats per minute. While not life-threatening, PSVT can cause symptoms like palpitations, dizziness, or shortness of breath.
Bradycardias and Heart Blocks
Bradycardias are arrhythmias where the heart rate is too slow, defined as below 60 beats per minute. Sinus bradycardia occurs when the heart’s natural pacemaker, the SA node, fires electrical impulses at a slower-than-normal rate. This can be a normal finding in highly conditioned athletes or during sleep.
Heart blocks, or atrioventricular (AV) blocks, disrupt electrical signal conduction from the atria to the ventricles. In first-degree AV block, the electrical signal is delayed, but all impulses still reach the ventricles. More severe forms, like second-degree and third-degree (complete) AV blocks, involve some or all impulses failing to reach the ventricles, causing a significantly slower and potentially independent ventricular rhythm.
Ventricular Arrhythmias
Ventricular arrhythmias originate in the heart’s lower chambers (ventricles). These types of arrhythmias are more serious than supraventricular ones due to the ventricles’ primary role in pumping blood to the body and lungs. Disruptions in ventricular rhythm can severely impair the heart’s ability to circulate blood, leading to severe consequences.
Ventricular Tachycardia (V-Tach)
Ventricular tachycardia (V-Tach) is a fast, regular heartbeat from abnormal electrical activity in the ventricles. In this condition, the ventricles beat so rapidly, between 150-250 beats per minute, that they do not have enough time to fill properly with blood before contracting. This inefficient pumping reduces the amount of blood circulated to the body, which can be a medical emergency. Sustained ventricular tachycardia, lasting more than 30 seconds, indicates underlying heart disease and can quickly progress to a more dangerous rhythm.
Ventricular Fibrillation (V-Fib)
Ventricular fibrillation (V-Fib) is a life-threatening arrhythmia where ventricles quiver rapidly and chaotically, not pumping blood effectively. The electrical signals become disorganized, leading to an uncoordinated twitching of the ventricular muscle fibers. This complete loss of effective pumping action means no oxygenated blood reaches the brain or other organs, making V-Fib a primary cause of sudden cardiac arrest. Immediate medical intervention, defibrillation, is required to restore a normal rhythm and prevent death.
Premature Ventricular Contractions (PVCs)
Premature ventricular contractions (PVCs) are common extra heartbeats originating prematurely in the ventricles. Individuals describe PVCs as a “skipped beat,” a “flip-flop” sensation, or a strong thump in the chest. These extra beats occur when an electrical impulse fires too soon in the ventricles, followed by a brief pause before the next normal beat, which feels stronger due to increased blood filling. While harmless in healthy individuals, numerous or complex PVCs can indicate an underlying heart condition or increase the risk of more serious arrhythmias in compromised hearts.
Diagnostic Methods for Classification
Diagnosing arrhythmias requires various tools to visualize and analyze the heart’s electrical activity. These methods range from quick snapshots to prolonged monitoring and even invasive mapping procedures. The choice of diagnostic method depends on the frequency and nature of a person’s symptoms.
Electrocardiogram (ECG or EKG)
An electrocardiogram (ECG or EKG) is a common, non-invasive test providing a snapshot of the heart’s electrical activity. Electrodes placed on the skin record electrical signals, which are then displayed as waves on a monitor or paper. An ECG can quickly reveal the heart’s rate and rhythm, identify patterns indicative of specific arrhythmias, and show details like P waves and QRS complexes that characterize different heartbeats.
Holter and Event Monitors
For arrhythmias that occur intermittently, wearable devices offer extended monitoring. A Holter monitor is a portable ECG device worn for 24 to 48 hours, continuously recording the heart’s electrical activity during daily routines. This allows for the capture of irregular rhythms that might not be present during a brief office ECG. Event recorders are similar but are worn for longer periods, up to 30 days, and only record when triggered by symptoms or automatically detect an abnormal rhythm.
Implantable Loop Recorder
For very infrequent arrhythmias, an implantable loop recorder (ILR) provides long-term monitoring. This small device is placed just under the skin in the chest and can continuously record heart rhythm for up to three years. ILRs are useful for diagnosing rare episodes, such as those causing unexplained fainting spells or cryptogenic strokes, by capturing the heart’s activity before, during, and after an event.
Electrophysiology Study (EPS)
An electrophysiology study (EPS) is an invasive procedure to map the heart’s electrical system and pinpoint complex arrhythmia origins. During an EPS, thin, flexible wires called catheters are inserted into blood vessels and guided into the heart. These catheters can record electrical signals from inside the heart and even induce arrhythmias to study them, helping doctors determine the best course of treatment, such as ablation.