The two bundles initially are together at a junction called the bundle of His. The right bundle carries nerve impulses that cause contraction of the right ventricle (the lower chamber of the heart) and the left bundle carries nerve impulses that cause contraction of the left ventricle. There are two bundle branches, right and left. Descriptionīundle branch block belongs to a group of heart problems called intraventricular conduction defects (IVCD). KEY TERMSĪtrioventricular node (AV node) - Highly specialized area of the heart muscle which transmits electrical impulses.īradycardia - A slow heart rate, usually under 60 beats per minute.īundle branch block (BBB) is a disruption in the normal flow of electrical pulses that drive the heart beat. Resources ORGANIZATIONSĪmerican Heart Association. For people with third-degree block, once the heart has been restored to its normal, dependable rhythm, most people live full and comfortable lives. Most people with first- and second-degree heart block don't even know they have it. Most people need the pacemaker for the rest of their lives. In an emergency, a temporary pacemaker can be used until an implanted device is advisable. Some second- and almost all third-degree heart blocks require an artificial pacemaker. A physical exam and ECG confirm the presence of heart block. Third-degree heart block usually results in symptoms such as fainting, dizziness and sudden heart failure, which require immediate medical care. Diagnosisĭiagnosis of first-, and second-degree heart block is made by observing it on an electrocardiograph (ECG). Young children who have received a forceful blunt chest injury, can experience first-, or second-degree heart block. If the ventricles beat more than 40 times per minute, symptoms are not as severe, but include tiredness, low blood pressure on standing, and shortness of breath. Symptoms include fainting, dizziness and sudden heart failure. Third-degree heart block is a serious condition that affects the heart's ability to pump blood effectively. Second-degree block can occasionally progress to third-degree. Some cases of second-degree heart block may benefit from an artificial pace-maker. First-degree heart block produces no symptoms. The condition may be caused by rheumatic fever, some types of heart disease and by some drugs. It is seen in teenagers, young adults and in well-trained athletes. Causes and symptomsįirst-degree heart block is fairly common. Though this impulse usually keeps the heart from stopping entirely, it is too slow to be an effective pump. When no signals can travel through the AV node, the heart uses its backup impulse generator in the lower portion of the heart. Third-degree block, also called complete heart block, is the most serious. If the blockage is frequent, it results in an overall slowing of the heart called bradycardia. The block may affect every other beat, every second or third beat, or be very rare. In second-degree heart block, not every impulse reaches its destination. In first-degree heart block, the signal is just slowed down a little as it travels along the defective part of the conduction system so that it arrives late traveling from the atrium to the ventricle. These delays are classified according to their severity. Just as on a highway, there are occasionally some delays getting the impulse from one point to another. The main junction of this system is called the atrioventricular node (AV node). The muscles of the heart contract in a rhythmic order for each heart beat, because electrical impulses travel along a specific route called the conduction system. They are further classified as first-, second-, or third-degree block. Heart block refers to a delay in the normal flow of electrical impulses that cause the heart to beat.
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