The heart operates as a highly efficient pump, dependent on precise electrical coordination. Every beat is initiated by an electrical signal that ensures the four chambers contract in a synchronized pattern. When this electrical signaling system malfunctions, the heart’s rhythm is compromised, reducing its ability to pump blood effectively.
How the Heart’s Electrical System Works
The heart’s electrical sequence begins in the sinoatrial (SA) node, a cluster of specialized cells in the upper wall of the right atrium. The SA node is the heart’s natural pacemaker, spontaneously generating an electrical impulse 60 to 100 times per minute in a resting adult. This signal spreads across the atria, causing them to contract and push blood into the ventricles.
The electrical wave then converges at the atrioventricular (AV) node, situated between the atria and the ventricles. The AV node briefly delays the signal transmission. This pause ensures the atria have emptied their blood into the ventricles before the lower chambers are signaled to contract.
From the AV node, the impulse travels rapidly down the interventricular septum through the bundle of His, which quickly branches into the left and right bundle branches. These branches distribute the signal through a network of specialized fibers known as the Purkinje fibers, which penetrate the ventricular muscle walls. The signal’s quick distribution ensures the powerful lower chambers, the ventricles, contract simultaneously to eject blood to the lungs and the rest of the body.
Defining and Categorizing Rhythm Disorders
The medical term used to describe any disruption to this organized electrical sequence, resulting in the heart being “out of sync,” is an arrhythmia. An arrhythmia occurs when the heart’s electrical impulses are too fast, too slow, or erratic, preventing efficient blood pumping. The normal, coordinated rhythm is known as sinus rhythm, and any deviation is considered a rhythm disorder.
Rhythm disorders are broadly categorized based on heart rate. A heart rate consistently over 100 beats per minute (bpm) at rest is classified as tachycardia. Conversely, a resting heart rate below 60 bpm is referred to as bradycardia.
Arrhythmias are also categorized by the pattern of the beat, such as an irregular or chaotic rhythm. Atrial fibrillation, for example, involves rapid, disorganized electrical signaling in the atria, causing them to quiver rather than contract effectively. Other irregularities include ectopic beats, which are premature contractions originating outside the SA node.
Underlying Causes and Contributing Risk Factors
The malfunction of the heart’s electrical system can be traced to two primary areas: structural heart disease or the influence of external factors. Structural causes involve physical changes to the heart muscle or damage to the conduction pathways. Prior events, like a heart attack, can leave scar tissue that blocks or redirects electrical signals, often leading to serious arrhythmias.
Conditions that chronically stress the heart, such as long-standing high blood pressure, can cause the heart muscle to thicken or enlarge, a change that disrupts the normal flow of electricity. Coronary artery disease restricts blood flow, potentially starving sections of the heart muscle of oxygen and impairing the function of pacemaker cells. Heart failure or congenital heart defects, which are structural issues present from birth, can also alter the electrical environment.
External and lifestyle factors can destabilize the electrical system even in a structurally normal heart. An imbalance in electrolytes, such as potassium, sodium, or calcium, directly interferes with the electrical charges needed for heart cells to fire correctly. Endocrine issues like an overactive or underactive thyroid gland release hormones that accelerate or slow the heart rate.
Certain lifestyle habits can also act as triggers by overstimulating the heart. Excessive consumption of stimulants like caffeine, alcohol, or nicotine can increase the heart’s excitability and provoke irregular beats. Additionally, medical conditions like obstructive sleep apnea and chronic stress or anxiety are known to strain the heart and increase the risk of developing a rhythm disorder.