Conduction Disorders

Updated:Nov 22,2016

Rhythm vs. Conduction
Your heart’s rhythm is its pace or beat. Conduction is the progression of electrical impulses through the heart which cause the heart to beat. You can have a conduction disorder without having an arrhythmia, but some arrhythmias arise from conduction disorders.

Common conduction disorders include:

Bundle Branch Block

How it works

  • Normally, the electrical impulse travels down both the right and left branches of the conduction system in the ventricles at the same speed. Thus, both ventricles contract at the same time.
  • Occasionally there's a block in one of the branches, so impulses must travel to the affected side by a detour that slows them down. That means one ventricle contracts a fraction of a second slower than the other.
Symptoms and diagnosis
If there's nothing else wrong,usually a person with bundle branch block shows no symptoms. But a bundle branch block shows up as an abnormality when the electrical impulses through the heart are recorded with an electrocardiogram (ECG).

Treatment
Usually no treatment is required, but your healthcare provider will want to see you regularly to be sure no other changes occur. You may have bundle branch block for many years and still feel fine, but it's important to have regular check-ups.

How it works

  • Normally, the electrical impulse travels down both the right and left branches of the conduction system in the ventricles at the same speed. Thus, both ventricles contract at the same time.
  • Occasionally there's a block in one of the branches, so impulses must travel to the affected side by a detour that slows them down. That means one ventricle contracts a fraction of a second slower than the other.
Symptoms and diagnosis
If there's nothing else wrong,usually a person with bundle branch block shows no symptoms. But a bundle branch block shows up as an abnormality when the electrical impulses through the heart are recorded with an electrocardiogram (ECG).

Treatment
Usually no treatment is required, but your healthcare provider will want to see you regularly to be sure no other changes occur. You may have bundle branch block for many years and still feel fine, but it's important to have regular check-ups.

arrhythmiaSometimes the electrical signal from the heart's upper chambers (atria) to lower chambers (ventricles) is impaired or doesn't transmit. There are several degrees of heart block. Watch an animation of heart block.

  • First-degree heart block occurs when the electrical impulse moves through the AV node more slowly than normal. The heart beat usually has a slower rate but may not cause noticeable symptoms or may cause light headedness and dizziness and may not require specific treatment. Certain drugs can cause first-degree heart block. These drugs include digitalis, beta-blockers, and calcium-channel blockers. Digitalis is one common drug that is used to slow down the heart rate. If it's taken in large amounts or for a long period of time (also known as digitalis intoxication), digitalis can cause first-degree heart block. Beta-blockers inhibit the part of the nervous system that speeds up the heart. This increases the conduction delay of the heart's electrical impulse and can cause first-degree heart block.

    Among their other effects, calcium-channel blockers have the ability to slow down the conduction of the AV node, resulting in heart block.  People with this type of block along with regular assessment by a physician, should also be taught to take their pulse and monitor it regularly to detect changes.
  • Second-degree heart block occurs when some electrical signals from the atria don't reach the ventricles, resulting in "dropped beats." Second degree heart block can be classified as Mobitz Type 1 or Mobitz Type 2.  Mobitz Type 1 is also commonly referred to as Wenckebach and may not cause noticeable symptoms. Symptoms associated with second degree heart block are chest pain, faintness (syncope), and palpitations, breathing difficulties, such as shortness of breath with exertion, rapid breathing, nausea, and fatigue. Second degree Type I may not require treatment but can be a forerunner for Type 2 and needs to be monitored on a regular basis as well as daily pulse checks by the patient. However, it can be a forerunner for Mobitz Type 2 and needs to be monitored by a physician. In Mobitz Type 2, the heart beat does not beat effectively and impacts the hearts’ ability to pump blood to the rest of the body.  Often times having a pacemaker inserted is necessary so the heart will beat effectively. 
  • Third-degree or complete heart block means that the heart's electrical impulse does not pass from the heart's upper to lower chambers at all. When this occurs, the heart does not beat correctly and cannot effectively move blood to the body. Symptoms for third-degree heart block reflect severity of the slow heart rate, fainting, dizziness, fatigue, shortness of breathe, and chest pain. Secondary pacemaker cells in the lower chambers will take over, causing the ventricles to contract and pump blood, but at a slower rate than when signals come from the sinoatrial node. Complete heart block in adults is caused by heart conditions or as a side effect of drug toxicity. An injury to the electrical conduction system during heart surgery also may cause heart block. People with third-degree heart block experience irregular and unreliable heart beats, which requires immediate medical attention involving a temporary pacemaker because of the potential for having a cardiac arrest. A permanent pacemaker would be indicated to treat complete heart block.

What is long QT syndrome (LQTS)?

  • Long Q-T Syndrome is a disorder of the heart's electrical system, like other arrhythmias. 
  • Since the hearts electric activity is controlled by the flow of ions (that is  electrically charged particles such as calcium, sodium, potassium and chloride), these ions move in and out of the cells of the heart. This flow is controlled by very small ion channels.
  • When the heart contracts, it emits an electrical signal. This signal can be recorded on an electrocardiogram (ECG) and produces a characteristic waveform.
  • The different parts of this waveform are designated by letters — P, Q, R, S and T.
  • The Q-T interval represents the time for electrical activation and inactivation of the ventricles, the lower chambers of the heart.
  • A doctor can measure the time it takes for the Q-T interval to occur (in fractions of a second) and can tell if it occurs in a normal amount of time. If it takes longer than normal, it's called a prolonged Q-T interval.
Who is likely to have it?
Long Q-T syndrome is an infrequent, hereditary disorder that can occur in otherwise healthy people. It usually affects children or young adults.
Some people acquire LQTS. Some medications can induce LQTS. Sometimes persons with LQTS have both the hereditary form and the acquired form. There are several types of medications that can cause LQTS, below are just a few:
  • Antihistamines and decongestants
  • Diuretics (pills that remove excess water from your body, example: potassium or sodium)
  • Certain antibiotics
  • Antiarrhythmic (anti abnormal heartbeat) medicines
  • Antidepressant and antipsychotic medicines
  • Cholesterol-lowering medicines and some diabetes medicines
Symptoms of LQTS
People with LQTS may not have any symptoms. People who do have symptoms often have:
  • Fainting (syncope)
  • Abnormal rate and/or rhythm of the heartbeat (arrhythmia), a fluttering feeling in the chest.
Prolonged Q-T interval may occur:
  • During physical activity or exercise
  • During intense emotion (such as fright, anger or pain)
  • When startled by a noise
  • With drugs known to prolong Q-T interval
Diagnosing LQTS
  • The doctor may recommend an exercise stress test.
  • Studies of otherwise healthy people with LQTS indicate that they had at least one episode of fainting by the age of 10.
  • The majority also had a family member with a long Q-T interval.
  • People with LQTS don't necessarily have a prolonged Q-T interval all the time. At the time that they have an electrocardiogram (ECG) (such as during a routine physical examination), the Q-T interval may actually be normal.
  • LQTS should be suspected even in healthy young people with normal routine ECG if there is a family history or unexplained fainting episodes. In any family where repeated episodes of fainting or a history of sudden death exists, an investigation of the cause, including LQTS, should be undertaken. Family testing with an ECG (first-line relatives) may be recommended.
Consequences of LQTS
  • Some arrhythmias are potentially fatal, causing sudden cardiac arrest.
  • Deafness may occur with one type of inherited LQTS.
  • Sometimes with LQTS, exercise can cause fatal arrhythmias can occur, so ask your Cardiologist about the level of exercise you can participate in.
Treatments for LQTS
May include medications such as beta blockers. Sometimes a surgical procedure is performed. Some people may benefit from an implantable cardiovertor defibrillator (ICD) or a pacemaker. Avoid drugs and electrolyte imbalance known to prolong the Q-T interval.


 




This content was last reviewed September 2016.

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