Arrhythmias happen when the electrical signals that coordinate your heartbeat malfunction. The cause can be as temporary as a night of heavy drinking or as deep-rooted as a gene you inherited from a parent. More than 59.7 million people worldwide live with atrial fibrillation alone, the most common type, and that number continues to climb.
How Your Heart’s Electrical System Works
Your heart has its own built-in pacemaker: a crescent-shaped cluster of cells called the sinus node, located at the top of the right atrium. These cells spontaneously generate electrical impulses without any signal from the brain. They do this through two internal “clocks” working together. One involves the flow of charged particles like potassium, sodium, and calcium across cell membranes. The other involves rhythmic pulses of calcium released from storage compartments inside the cells themselves. Together, these clocks set your resting heart rate.
Once the sinus node fires, the electrical impulse travels through the atria (upper chambers), passes through a relay station called the AV node, then spreads through a network of specialized fibers into the ventricles (lower chambers). This precise sequence is what produces a normal, coordinated heartbeat. An arrhythmia develops when something disrupts any point along this chain: the impulse might start in the wrong place, travel too slowly, get stuck in a loop, or fire at the wrong speed.
Heart Disease and Scarring
Coronary artery disease is one of the most common causes of arrhythmia. When blood flow to the heart muscle is reduced, either during an acute heart attack or from chronic narrowing of the arteries, the oxygen-starved cells become electrically unstable. Ischemia enhances the automatic firing of heart cells and creates uneven conduction speeds across the tissue. This sets up what cardiologists call “reentry circuits,” where electrical signals loop back on themselves instead of following a clean path forward.
Over time, chronic ischemia causes the heart muscle to remodel. Scar tissue (fibrosis) replaces healthy muscle, and the atria may stretch and dilate. Scar tissue doesn’t conduct electricity the way normal heart cells do, so electrical impulses have to detour around it. These detours create the inconsistencies in timing that sustain arrhythmias like atrial fibrillation. This is why people who have had a heart attack carry a higher long-term risk of rhythm problems, even after the acute event has healed.
Structural Changes to the Heart
You don’t need a heart attack to develop structural problems that trigger arrhythmias. Conditions that stretch, thicken, or weaken the heart muscle, collectively called cardiomyopathies, can do the same thing. Heart failure, valve disease, and high blood pressure all force the heart to work harder, and the chambers gradually enlarge or stiffen in response. This stretching activates a cascade of neurohormonal signals and oxidative stress that remodel the heart’s electrical wiring. The result is the same kind of patchy, disorganized conduction that creates fertile ground for abnormal rhythms.
Electrolyte Imbalances
The electrical signals in your heart depend on charged minerals moving in and out of cells in a precise sequence. When the blood levels of these minerals shift, the timing of each heartbeat changes with them.
Calcium has the strongest effect. Low calcium levels lengthen the electrical recovery phase of each heartbeat (measured on an EKG as the QT interval) by roughly 11.5 milliseconds on average. People whose calcium falls into the bottom 2% of the population see clinically meaningful changes, enough to raise the risk of a dangerous rhythm called torsades de pointes. Low potassium also lengthens this recovery phase, though much of that association is linked to blood pressure medications that deplete potassium as a side effect. Interestingly, sodium levels don’t appear to have a meaningful effect on heart rhythm.
Dehydration, kidney disease, prolonged vomiting or diarrhea, and certain diuretics are the most common reasons electrolytes drift out of range. This is one of the more fixable causes of arrhythmia: once levels are corrected, the rhythm disturbance often resolves.
Thyroid Disorders
An overactive thyroid gland is a well-established trigger for arrhythmias, particularly atrial fibrillation. Excess thyroid hormone puts the heart into a hyperadrenergic state, essentially mimicking the effects of a constant adrenaline surge. The mechanism is specific: thyroid hormone increases the number of beta-2 adrenergic receptors on heart muscle cells, making them more sensitive to stimulation. In primate studies, this receptor upregulation was directly associated with ventricular tachycardia.
People with hyperthyroidism typically have elevated resting heart rates, more frequent premature atrial beats, and reduced heart rate variability. The good news is that these changes often normalize once thyroid levels return to the normal range. Beta-blockers are used in the interim because they directly counteract the hyperadrenergic state driving the rhythm disturbance.
Inherited Electrical Disorders
Some people are born with ion channels in their heart cells that don’t work correctly. These inherited conditions, called channelopathies, can cause life-threatening arrhythmias even in young, otherwise healthy people.
- Long QT syndrome slows the electrical recovery of each heartbeat, increasing the risk of sudden, chaotic rhythms. It is caused by mutations in genes that control potassium, sodium, and calcium channels.
- Brugada syndrome affects the sodium channels and is responsible for a significant fraction of sudden cardiac arrests in people without obvious heart disease. A mutation in the SCN5A gene accounts for 15% to 30% of known cases, though many other genes contribute.
- Catecholaminergic polymorphic ventricular tachycardia (CPVT) triggers dangerous fast rhythms during exercise or emotional stress. It is most commonly linked to a mutation that disrupts calcium handling inside heart cells.
- Short QT syndrome is the mirror image of long QT: the electrical recovery phase is too brief, which also destabilizes the rhythm. It results from potassium channels that stay open too long or calcium channels that don’t open enough.
These conditions often run in families and can sometimes be detected on a routine EKG before symptoms ever appear. They are a key reason unexplained fainting episodes or a family history of sudden cardiac death in young relatives are taken seriously.
Alcohol and “Holiday Heart Syndrome”
Binge drinking is one of the most reliable short-term triggers for atrial fibrillation. The pattern is common enough that it has its own name: holiday heart syndrome. People who consumed more than two drinks within four hours were over 3.5 times as likely to have an AFib episode compared to those who hadn’t been drinking.
A 2024 study of nearly 200 adults in Germany, averaging around age 30, tracked heart rhythms before and after a planned night of heavy drinking. Heartbeat changes peaked about four hours after drinking began, and roughly 5% of participants developed some form of rhythm irregularity within 48 hours. On the flip side, people who habitually drank 10 or more drinks per week were able to lower their AFib risk simply by cutting back. Alcohol’s effect on heart rhythm is dose-dependent and, for many people, reversible.
Medications That Affect Heart Rhythm
A surprisingly wide range of prescription and over-the-counter drugs can lengthen the QT interval and increase arrhythmia risk. The list includes certain antibiotics (like ciprofloxacin), antidepressants (like fluoxetine), antihistamines (like bilastine), pain medications containing codeine, and even some herbal supplements like St. John’s Wort. The risk is usually small for any single drug, but it increases when multiple QT-prolonging medications are taken together or when electrolyte levels are already low.
The nonprofit organization CredibleMeds maintains a regularly updated database of medications linked to QT prolongation. If you take several medications and have been told you’re at risk for arrhythmias, this is a resource worth knowing about.
Age-Related Wear and Conduction System Disease
Even without a specific disease, the heart’s conduction system degenerates over time. The specialized cells that generate and relay electrical impulses gradually become surrounded by fibrous tissue, slowing conduction and making the system less reliable. This age-related degeneration is one of the primary reasons arrhythmias become more common with each passing decade. It can affect the sinus node (leading to a slow heart rate) or the pathways below it (causing electrical signals to get delayed or blocked on their way to the ventricles).
This process is accelerated by high blood pressure, diabetes, and other chronic conditions that put extra strain on the heart over years. It’s also why arrhythmias in older adults often have no single dramatic cause. Instead, they reflect the cumulative effect of decades of gradual electrical and structural remodeling.