How it works

• Normally, the electrical impulse travels down both the right and left branches 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
Usually if there's nothing else wrong, 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 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
Usually if there's nothing else wrong, 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.

Sometimes 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.

• 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 and may not cause noticeable symptoms. Certain heart medicines such as digitalis can slow conduction of the impulse from the atria to the ventricles and cause first-degree AV block.
• Second-degree heart block occurs when some electrical signals from the atria don't reach the ventricles, resulting in "dropped beats."
• 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, bradycardia (slow heartbeat) may result. Secondary pacemaker cells in the lower chambers may 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 most often caused by heart disease or as a side effect of drug toxicity. Heart block also can be present at or even before birth (congenital heart block). An injury to the electrical conduction system during heart surgery also may cause heart block.

How it works

• 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 (LQTS) is an infrequent, hereditary disorder that can occur in otherwise healthy people. It usually affects children or young adults.

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)

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

• 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.

Consequences of LQTS

• Some arrhythmias are potentially fatal, causing sudden cardiac arrest.
• Deafness may occur with one type of inherited LQTS.

Treatments for LQTS
May include medications such as beta blockers. Sometimes a surgical procedure is performed. Some people may benefit from an implantable defibrillator. Avoid drugs and electrolyte imbalance known to prolong the Q-T interval.