Normal electrical conduction through the heart muscle takes a predicted pathway. It travels from the Sinoatrial node (SA node) to the Atrioventricular node (AV node) to the Bundle of His and then onto the left and right bundle branches (usually in a left to right pattern), ultimately ending up in the Purkinje fibres. Additionally, the Left Bundle has an anterior and posterior component called a fascicle. In normal cardiac electrophysiology, the electrical conduction occurs from left to right, essentially stimulating the left bundle, and left ventricle first. This chapter will discuss the syndromes that result in abnormal conduction at every step of the electrical pathway, the aberrations that are manifested in the ECG as a result and the relevance of each abnormality in a clinical setting. Abnormalities that manifest outside this conduction pathway, congenital and acquired will also be captured in this chapter.
Types of Conduction Disorders:
There are three types of conduction disorders. Here’s what to know about them.
Bundle branch block
In a normal heart, the electrical impulses travel down right and left sides at the same time, causing them to contract in unison. When there's a block in one branch, the impulses there are slightly delayed. Since both sides don't contract together, Mayo Clinic explains that this makes it difficult in some cases for the heart to efficiently pump blood.
Most people don’t notice any symptoms associated with bundle branch block, but some may have fainting spells.
Treatment usually isn’t needed for bundle branch block, but treatments may be recommended underlying health conditions like high blood pressure or heart disease that caused it. Bundle branch block doesn't usually cause problems, but it's important to have regular checkups to make sure that no changes occur and the disorder doesn't progress.
A normal heartbeat is initiated by an electrical signal that comes from the heart’s natural pacemaker, the sinoatrial (SA) node, located at the top of the right atrium. The electrical signal travels through the atria and reaches the atrioventricular (AV) node. After crossing the AV node, the electrical signal passes through the bundle of His. This bundle then divides into thin, wire-like structures called bundle branches that extend into the right and left ventricles. The electrical signal travels down the bundle branches and eventually reach the muscle cells of the ventricles, causing them to contract and pump blood to the body. Heart block occurs when this passage of electricity from top to bottom of the heart is delayed or interrupted.
You can't depend on symptoms to know when someone has a heart block, especially if it's minor, but the Heart Rhythm Society website says fainting, dizziness, chest pain, and shortness of breath could be signs of heart block. Some factors may raise the risk of heart block, including heart valve abnormalities or surgery, medications, or Lyme disease. There are three degrees of heart block.
In addition to these three degrees, bundle branch block is also considered to be a form of heart block.
Long QT syndrome
Long QT syndrome (LQTS) is a disorder that attacks the heart’s electrical activity. It causes sudden, dangerous arrhythmias (irregular heartbeats) after exercise or anything else that causes stress on the heart, like intense emotion. The National Center for Biotechnology Information explains that it is caused by mutations of genes, is hereditary, and usually occurs in children or young adults who are otherwise healthy. Patients may not have symptoms leading up to an episode.
In some cases, the arrhythmias caused by LQTS can lead to cardiac arrest and be fatal. LQTS can be treated with surgery or by taking beta blockers. People who are more prone to episodes may be given an implantable defibrillator. Anyone with LQTS should not use recreational drugs.
Treatment with Pacemaker:
Often, a pacemaker device can correct the problem. A pacemaker is a small device that sends electrical impulses to the heart muscle to maintain a suitable heart rate and rhythm. A pacemaker may also be used to treat fainting spells (syncope), congestive heart failure, and, rarely, hypertrophic cardiomyopathy.
It is implanted just under the skin of the chest during minor surgery.
The pacemaker has two parts: the leads and a pulse generator. The pulse generator houses the battery and a tiny computer and resides just under the skin of the chest. The leads are wires that are threaded through the veins into the heart and implanted into the heart muscle. They send impulses from the pulse generator to the heart muscle, as well as sense the heart's electrical activity.
Each impulse causes the heart to contract. The pacemaker may have one to three leads, depending on the type of pacemaker needed to treat your heart problem.