The four types of arrhythmias are supraventricular arrhythmias, ventricular arrhythmias, bradyarrhythmias, and premature contractions. Each type is defined by where in the heart the irregular rhythm starts and whether the heart beats too fast, too slow, or simply out of sequence. Some are harmless and barely noticeable, while others are medical emergencies.
Supraventricular Arrhythmias
Supraventricular arrhythmias originate in the upper chambers of the heart, called the atria. The most common and well-known of these is atrial fibrillation (AFib), which affects roughly 52.5 million people worldwide. In AFib, the electrical signals that normally coordinate the upper chambers become chaotic. The atria stop contracting in an organized pattern, which causes the lower chambers to beat irregularly and often too fast.
A related condition, atrial flutter, also speeds up the upper chambers but in a more regular, predictable pattern. In both cases, heart rates can climb as high as 250 to 350 beats per minute in the atria, and the overall heart rate frequently exceeds 100 beats per minute. Symptoms overlap significantly: racing or pounding pulse, palpitations, dizziness, fatigue, shortness of breath, and sometimes chest pressure. Some people feel confused or faint. Others have no symptoms at all and only discover the arrhythmia during a routine exam.
AFib is particularly important to identify because it significantly raises the risk of stroke. When the upper chambers quiver instead of contracting fully, blood can pool and form clots that travel to the brain.
Ventricular Arrhythmias
Ventricular arrhythmias start in the heart’s lower chambers, the ventricles, and they tend to be the most dangerous category. The ventricles are responsible for pumping blood out to the lungs and the rest of the body, so when their rhythm goes haywire, the consequences can be immediate and severe.
Ventricular tachycardia is a rapid, regular rhythm originating in the lower chambers. It can sometimes resolve on its own, but it can also deteriorate into ventricular fibrillation, a life-threatening condition where out-of-control electrical signals cause the ventricles to quiver and twitch rather than pump blood. Ventricular fibrillation is the rhythm behind most cases of sudden cardiac arrest. Without emergency treatment (typically a defibrillator shock), it is fatal within minutes. These arrhythmias usually require medical care right away and are the reason automated external defibrillators (AEDs) are placed in airports, gyms, and public buildings.
Bradyarrhythmias
Bradyarrhythmias are rhythms where the heart beats too slowly, generally below 60 beats per minute at rest. This is sometimes perfectly normal. Young, physically fit people often have resting heart rates in the 50s or even 40s because their hearts pump efficiently enough to meet the body’s needs with fewer beats.
Bradyarrhythmias become a problem when the slow rate means organs aren’t getting enough blood. Symptoms include fatigue, dizziness, lightheadedness, fainting, and shortness of breath during activity. Common causes include age-related changes to the heart’s electrical system, damage from a heart attack, or problems with the heart’s natural pacemaker (the node that initiates each heartbeat). When a slow rhythm causes symptoms and doesn’t improve, treatment often involves an implanted pacemaker that delivers small electrical pulses to keep the heart beating at an adequate rate.
Premature Contractions
Premature contractions are extra heartbeats that fire earlier than expected. The signal to beat arrives too soon, creating a brief pause followed by a stronger-than-normal beat when the heart returns to its regular rhythm. This is the classic “skipped beat” sensation, and it is the most common type of arrhythmia.
There are two subtypes. Premature atrial contractions (PACs) start in the upper chambers, while premature ventricular contractions (PVCs) start in the lower chambers. Both are extremely common in children, teenagers, and adults. In most cases, no underlying cause is found, and the extra beats go away on their own without treatment. Occasionally, premature contractions are linked to heart disease or injury, so persistent or frequent episodes may prompt further testing. They can also act as a trigger for other arrhythmias.
What Raises Your Risk
Some risk factors apply broadly across all four types. Age is the biggest one: as the heart ages, scarring and the effects of other chronic conditions make irregular rhythms more likely. Older adults are also more likely to have high blood pressure, heart failure, diabetes, or thyroid disease, all of which increase arrhythmia risk. Family history matters too. Arrhythmias can run in families, especially certain inherited conditions that affect the heart’s electrical wiring.
Lifestyle habits play a measurable role. Smoking, heavy alcohol use (more than two drinks a day for men, one for women), and stimulant drugs like cocaine or amphetamines all raise risk. Even some prescription medications, including certain antibiotics, blood pressure drugs, mental health medications, and over-the-counter allergy and cold medicines, can trigger arrhythmias in some people. Other health conditions that stress the heart, such as sleep apnea, obesity, lung disease, kidney disease, and viral infections like the flu or COVID-19, also contribute.
Day-to-day triggers can set off episodes in people who are already prone. These include caffeine, dehydration, low blood sugar, electrolyte imbalances (particularly low potassium, magnesium, or calcium), intense physical activity, and strong emotional stress or sudden surprises.
How Arrhythmias Are Detected
Many arrhythmias are intermittent, which makes catching them tricky. A standard electrocardiogram (EKG) records the heart’s electrical activity for about 10 seconds, so it only works if the arrhythmia happens to occur during that snapshot. For rhythms that come and go, a Holter monitor can record continuously for 24 to 48 hours.
When episodes are rare or unpredictable, an implantable loop recorder offers a longer window. This small device is placed just under the skin of the chest and records the heartbeat nonstop for up to three years. It can catch brief or infrequent irregular rhythms that other devices miss, which is why it’s often recommended for people with unexplained fainting, unexplained strokes, or suspected AFib that hasn’t been confirmed yet.