heart and blood vessel disorders
Atrioventricular Block
Classification of Atrioventricular Block
Atrioventricular block is classified as First-degree: Electrical conduction to the ventricles is delayed Second-degree: Electrical conduction is intermittently blocked Third-degree (complete): Electrical conduction is completely blocked In first-degree atrioventricular block, every electrical impulse from the atria reaches the ventricles, but each is slowed for a fraction of a second as it moves through the atrioventricular node. First-degree atrioventricular block is common among well-trained athletes, teenagers, young adults, and people with a highly active vagus nerve. This disorder rarely causes symptoms and does not require treatment. 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 ventricles must then undergo an electrical change to get ready for the next heart beat. This electrical 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 weaker 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. For first-degree block, conduction between the atrium (P) and ventricle (QRS) is slowed without skipped beats. In second-degree atrioventricular block, only some electrical impulses reach the ventricles. The heart may beat slowly, irregularly, or both. There are two types of second-degree atrioventricular block, type 1 and type 2. Type 1 may be present in young, athletic people, but type 2 always indicates heart disease is present. Sometimes second-degree atrioventricular block progress to third-degree atrioventricular block. In third-degree atrioventricular block, no impulses from the atria reach the ventricles, and the ventricular rate and rhythm are controlled by the atrioventricular node, bundle of His, or the ventricles themselves. These substitute pacemakers are slower than the heart’s normal pacemaker (sinus or sinoatrial node) and are often irregular and unreliable. Thus, the ventricles beat very slowly—less than 50 beats per minute and sometimes as slowly as 30 beats per minute. Third-degree atrioventricular block is a serious abnormal heart rhythm (arrhythmia) that can affect the heart’s pumping ability. Fatigue, dizziness, and fainting are common. Symptoms are less severe when the ventricles beat faster than 40 beats per minute. In third-degree atrioventricular block, the atria (p) beat independently of the ventricles (QRS). 