Overview of Abnormal Heart Rhythms – Heart and Blood …

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The sinoatrial (sinus) node (1) initiates an electrical impulse that flows through the right and left atria (2), making them contract. When the electrical impulse reaches the atrioventricular node (3), it is delayed slightly. The impulse then travels down the bundle of His (4), which divides into the right bundle branch for the right ventricle (5) and the left bundle branch for the left ventricle (5). The impulse then spreads through the ventricles, making them contract.

An electrocardiogram (ECG) represents the electrical current moving through the heart during a heartbeat. The current's movement is divided into parts, and each part is given an alphabetic designation in the ECG.

Each heartbeat begins with an impulse from the heart's pacemaker (sinus or sinoatrial node). This impulse activates the upper chambers of the heart (atria). The P wave represents activation of the atria.

Next, the electrical current flows down to the lower chambers of the heart (ventricles). The QRS complex represents activation of the ventricles.

The electrical current then spreads back over the ventricles in the opposite direction. This activity is called the recovery wave, which is represented by the T wave.

Many kinds of abnormalities can often be seen on an ECG. They include a previous heart attack (myocardial infarction), an abnormal heart rhythm (arrhythmia), an inadequate supply of blood and oxygen to the heart (ischemia), and excessive thickening (hypertrophy) of the heart's muscular walls.

Certain abnormalities seen on an ECG can also suggest bulges (aneurysms) that develop in weak areas of the heart's walls. Aneurysms may result from a heart attack. If the rhythm is abnormal (too fast, too slow, or irregular), the ECG may also indicate where in the heart the abnormal rhythm starts. Such information helps doctors begin to determine the cause.

An electrocardiogram (ECG), seen on the right, represents movement of electrical current (depicted in green) through the heart during a heartbeat. The first wave of the ECG, designated P, represents initiation of the heartbeat in the upper chambers of the heart (atria). The QRS complex represents movement of the electrical current through the lower chambers of the heart (ventricles). The T wave represents the recovery phase, in which the electrical current spreads back over the ventricles in the opposite direction. The heart, seen on the left, is beating in time with the ECG. Oxygen-depleted (blue) blood is pumped from the heart to the lungs, which supply oxygen. Oxygen-enriched (red) blood returns from the lungs to the heart and is pumped throughout the body.

Heart rhythm problems can sometimes be helped with drugs, but some people require a pacemaker. Special pacemakers with three wires can restore the normal sequence of heart chamber contractions (cardiac resynchronization therapy).

Artificial pacemakers are electronic devices that act in place of the hearts natural pacemaker (the sinus or sinoatrial node). They generate electrical impulses that initiate each heartbeat. Pacemakers consist of an impulse generator (that includes the battery) and wires that connect the pacemaker to the heart.

An artificial pacemaker is implanted surgically. After a local anesthetic is used to numb the insertion site, the wires (leads) that connect the pacemaker are usually inserted into a vein near the collarbone and threaded toward the heart. Through a small incision, the impulse generator, which is about the size of a silver dollar, is inserted just under the skin near the collarbone and connected to the wires. The incision is stitched closed. Usually, the procedure takes about 30 to 60 minutes. The person may be able to go home shortly afterward or may briefly stay in the hospital. The battery for a pacemaker usually lasts 10 to 15 years. Nevertheless, the battery should be checked regularly. Battery replacement is accomplished by replacing the impulse generator and is a quick procedure.

There are different types of pacemakers. Most are capable of sensing the heart's electrical activity. They allow the heart to beat naturally and do not start pacing unless the heart skips a beat or begins to beat at an abnormal rate. Doctors program the pacemaker before it is implanted. The programming determines what events trigger pacing and at what heart rate. Doctors can also reprogram the pacemaker after it is implanted using a device held against the skin. Some pacemakers can adjust their rate depending on the wearers activity, increasing the heart rate during exercise and decreasing it during rest.

Sometimes an electrical shock to the heart can stop a fast arrhythmia and restore normal rhythm. Using an electrical shock for this purpose is called cardioversion.

The heart is a muscle that contracts in rhythmic sequence for the duration of our lifetime. Each beat is stimulated by an electrical signal that is generated by the hearts conduction system. A normal heart beats 60 to 100 times per minute.

In a normal heartbeat, the hearts electrical signal follows a specific pathway through the heart. The signal begins in the sinoatrial node, or SA node, located in the right atrium. The SA node triggers the atria to contract, pushing blood into the ventricles. The electrical signal then travels through the atrioventricular node, or AV node, and into the ventricles. The signal now causes the ventricles to contract, pumping blood into the lungs and body.

Sometimes, a problem with the conduction system causes the heart to beat too fast, too slow, or to have an erratic or irregular beat. Radiofrequency ablation is a medical procedure used to correct an arrhythmia, or irregular heart beat.

Before ablation, electrophysiology studies will be obtained to identify the exact area of the heart that needs to be treated. During the ablation procedure, a catheter is inserted into an artery in the leg, and is guided through the artery and into the heart. Once the catheter reaches the target site in the heart, electrodes at the tip of the catheter emit radio energy. This energy will heat and destroy the heart tissue causing the abnormal rhythm. In most cases, the heart returns to a normal rhythm following ablation. However, some patients may still require medication or pacemaker insertion.

There are several potential complications associated with this procedure that should be discussed with a doctor prior to surgery.

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Overview of Abnormal Heart Rhythms - Heart and Blood ...