Understanding Arrhythmia

Anatomy of the heart

The heart is a muscular organ that pumps blood throughout the body. The heart has four chambers that work together, relaxing and contracting with every heartbeat. The upper chambers of the heart, called the atria, receive blood from the veins. The lower chambers of the heart, called the ventricles, pump blood into the arteries. The heart receives blood from the body through the superior and inferior vena cava entering the right atrium. From the right atrium blood passes into the right ventricle and is pumped through the pulmonary arteries and into the lungs where it becomes oxygenated. This oxygenated blood flows back into the heart through the pulmonary veins and enters the left atrium. Blood empties from the left atrium into the left ventricle. When the left ventricle is full, it contracts to deliver oxygen-rich blood through the aorta and into the body. There are four valves within your heart. These valves open and close tightly to keep blood flowing in one direction. The mitral valve and tricuspid valve lie between the atria and the ventricles. The pulmonary valve is located between the right ventricle and the pulmonary artery. The aortic valve is located between the left ventricle and the aorta.

The electrical system

Your heart relies on its own electrical conduction system to signal the heart to beat. Normally, electrical impulses travel from the top of your heart to the bottom of your heart down specific pathways. These impulses cause the atria and ventricles to work together, relaxing, filling, and pumping with each heartbeat. A properly functioning conduction system provides a regular heart rate that efficiently pumps blood throughout the body, including the heart and lungs.

In a normal heart, an electrical signal begins in the sinoatrial (SA) node and travels down both the right and left atrium causing the atria to contract. The electrical activity continues on from the atria to the ventricles through the atrioventricular (AV) node and bundle of His (a collection of heart muscle cells specialized for electrical conduction). From here, the impulse travels through the ventricles by way of the right and left bundle branches and ends in a network of fibers called the Purkinje fibers. This causes the ventricles to contract. This forces blood out of the heart to the lungs and the body. The pulmonary veins empty oxygenated blood from the lungs to the left atrium. A normal heart beats in a constant rhythm -- about 60 to 100 times per minute at rest.

An arrhythmia is an irregular heartbeat ­– the heart may beat too fast (tachycardia) too slowly (bradycardia), too early (premature contraction) or too irregularly (fibrillation). Arrhythmias are heart-rhythm problems – they occur when the electrical impulses to the heart that coordinate heartbeats are not working properly, making the heart beat too fast/slow or inconsistently.

Many heart arrhythmias are harmless. We all occasionally experience irregular heartbeats, which may feel like a racing heart or fluttering. Some arrhythmias, however, especially if they veer too far from a normal heartbeat or result from a weak or damaged heart, may cause troublesome and even potentially fatal symptoms.

Rapid arrhythmias are called tachycardias, while slow ones are called bradycardias. Irregular arrhythmias – when the heartbeat is irregular – are called fibrillations, as in atrial or ventricular fibrillation. When a single heartbeat occurs earlier than it should it is called premature contraction.

types of arrhythmia
symptoms of arrhythmia
causes of arrhythmia