Heart Block is a condition that causes delays or interruptions in the electrical conduction system of the heart. It is considered a form of arrhythmia, or a problem with the regular rhythm or rate of an individual’s heartbeat, and can occur anywhere along this electrical system.
A typical healthy heart contracts sixty to eighty times per minute for the purpose of pushing blood through the ventricles into the circulation system throughout the body. Each heartbeat/contraction is controlled by the initiation of an electrical signal created in the specialized group of cells found in the upper chamber of the right atrium of the heart referred to as the sinoatrial node, or SA node. The signal is passed down to the atrioventricular node, or AV node, another set of specialized conducting cells, down through the Bundle of His. His is a bundle of fibers that branch throughout the ventricles of the heart and cause a contraction. A heart block disrupts this system which in turn causes an individual have a slower than normal heart rate identified by an irregular pattern, to varying degrees.
These regulatory signals can be either partially or completely blocked. The three types of heart block are categorized as first-, second- or third-degree and is determined by how undermined the conduction has become.
In first-degree heart block, there is a slight disruption in the electrical signals from the atrium to the ventricles causing slower but successful conduction. Few symptoms emerge and treatment is usually not required. Certain medication can be responsible for this such as beta blockers, and the condition is often also found in athletes.
In second-degree heart block, there a more pronounced disruption in the conduction of electrical signals, and is separated into 2 divisions: Mobitz Type I and Mobitz Type II.
Mobitz Type I, or Wenckebachs block, is the minor form of second-degree heart block and is characterized by the electrical signals gradually moving slower with each contraction, with the ventricles not receiving all the signals from the atrium, until a skipped beat occurs.
Mobitz Type II is the more serious form of second-degree blockage and has an irregular pattern of missed signals to the ventricles. Pacemakers are often needed to maintain heart rate.
Third-degree heart block is also called complete heart block and is the most serious. Conduction from the atrium to the ventricles does not occur, and the ventricles attempt to compensate by creating electrical signals for contraction. The heart is able to pump blood, but is not coordinated with the atria and operates at a much slower pace. The risk of death from cardiac arrest is high and often results in emergency treatment with a pacemaker to maintain regular heart function.
Symptoms resulting from both second- and third-degree heart block include fainting, shortness of breath, fatigue, dizziness, palpitations and chest pain.
This disease can be congenital or acquired. While the most common cause of acquired heart block is damage from myocardial infarction; rheumatic fever, heart failure, coronary artery disease, myocarditis and cardiomyopathy also play a role. Exposure to toxins, an overly active vagus nerve and certain surgeries have also been shown to disrupt the electrical conduction.
Cardiologists will typically use an EKG to monitor the timing, rhythm and strength of the electrical signals to initially diagnose heart block. Following this, a Holter monitor may be worn for twenty-four to forty-eight hours or an event monitor may be worn for up to two months. These portable EKG’s provide test results from a longer period of time to further assist in the diagnoses. Other possible diagnostic tools include an echocardiogram, tilt-table tests and electrophysiology tests.
Treatments when symptomatic include alleviating the underlying factors contributing to the disease such as hypertension, or stopping or replacing certain medications. For some second- and most third-degree heart block patients, a pacemaker is recommended to restore and maintain a normal heart rate.
References
Explore Heart Block (2010). National Heart Lung and Blood Institute National Institute of Health. Retrieved on December 4, 2011 from: http://www.nhlbi.nih.gov/health/health-topics/topics/hb/treated.html
Heart Block (2011). Cleveland Clinic. Retrieved on December 4, 2011 from: http://my.clevelandclinic.org/heart/disorders/electric/heart_block.aspx
What is Heart Block? (2010). Medical News Today MediLexicon International LTD. Retrieved on December 4, 2011 from: http://www.medicalnewstoday.com/articles/180986.php
