what is long QT?

Answer 1

It is an irregularity in the cardiac action potential in which the heart takes longer than usual to reset before another beat.

It makes one susceptible to a potentially lethal type of arrythmia called "Torsade de Pointes" or twisting of points of the EKG.

Their is an inherited form of long QT which is due to a genetic mutation in a potassium channel in the heart that is involved in repolarization of the heart. It is more prevalent in women then in men.

There is also "acquired Long QT" which comes from taking certain types of drugs, including some antiarrhythmic drugs, some antifungal and some antihistamines can trigger this lethal reaction in people with Long QT.

If someone with the genetic form takes those drugs it is especially dangerous.

Answer 2

Long QT syndrome is a inherited defect in the heart rhythm that predisposes syncope(fainting) without warning,dizziness and seizures and sudden death. The name comes from the QT segment in the ECG tracing,that it takes longer for the heart to recharge itself.Certain conditions may trigger this abnormal cardiac rhythm,such as intense physical labor and exercise,being suddenly startled or badly frightened.Treatments include beta blockers medications or a implantable "pace-maker"Take care. SW RNP

Answer 3

Prolonged QT is something seen on EKG, and basically means that the heart's ventricles are taking longer than normal to relax (i.e. repolarize). The problem with this is that the ventricular muscle cells might start to contract in a non-coordinated and rapid fashion (e.g. ventricular arrythrmia, tachycardia, or Torsades de Pointes), which may very quickly lead to heart failure.

Answer 4

read on this, hope it helps, http://www.long-qt-syndrome.com/ekg_readout.html

Answer 5

LONG QT-INTERVAL SYNDROMES

What Are the Symptoms?

Dizziness, syncope, or sudden death are the most common symptoms. They are due to TDP, and usually occur during physical exertion or emotional excitement like anger, fear, or startle. Symptoms, however, may occur during sleep, or arousal from sleep. Common startle events include sirens, telephones, and alarm clocks. It is less common for syncope or sudden death to occur when the person is awake and at rest. The particular trigger for the symptoms depends to some degree on the specific gene abnormality. In LQTS1, swimming provokes symptoms in more than 15% of victims (see the section below on genetics).

Exercise-induced syncope usually occurs during the actual exercise, but may occur seconds or minutes later. In patients with syncope, TDP reverts spontaneously to normal, usually within about one minute or less. When this occurs, the patient quickly regains consciousness, usually without disorientation or residual symptoms. When TDP persists for a longer time, however, it degenerates into VF. The outcome is death unless prompt defibrillation is provided.

At least one-third of the patients with LQTS are asymptomatic. For some, their first presentation may be their last – sudden unexplained cardiac arrest. And, some patients have just one or two syncopal spells as children, and none thereafter. Others have many episodes over a number of years.

The symptoms may begin as early as the first days or weeks of life, or as late as middle age. Most commonly, however, the symptoms first occur during preteen and teenage years. The symptoms start earlier in males than females, beginning on average at approximately eight years old in males and 14 years old in females. Because many affected persons never have symptoms, the absence of a history of syncope or sudden death in a family does not guarantee the absence of LQTS in the family.

How Is the Diagnosis Made?

Always suspect LQTS in any patient with dizziness, syncope, or aborted sudden death especially if the event occurred in the face of exertion, emotion, or stress. Many, though, far from all, cases of LQTS may be diagnosed by a combination of patient history, family history, and the 12-lead EKG.

Take a thorough history of the event – many lay-persons erroneously describe syncopal spells as seizures, especially if the victim has a myoclonic jerk or two following loss of consciousness. Look for “key family facts” such as unexplained fatal accidents (e.g., drowning, unexplained falls), SIDS, familial epilepsy, familial fainting spells.

Thirty percent of persons with known LQTS have normal QT intervals on the EKG. Despite this limitation, it behooves the clinician to obtain an EKG on any patient who has unexplained dizziness, syncope, or aborted sudden death. If the QT interval is prolonged, further evaluation with a cardiologist is recommended. Additional work-up may involve treadmill testing, genetic analysis (family pedigree, molecular analysis of DNA), or both. As a general rule, obtain screening EKGs on all first-degree relatives (e.g., parents, siblings) of a known affected patient.

When an EKG is obtained, regardless of the patient’s age, pay particular care to its proper interpretation. Ample data have shown that QT intervals measured automatically by the EKG machine are unreliable. A “human touch” is absolutely necessary! The measured QT interval must be corrected for the heart rate. Typically, this is done mathematically using Bazzett’s formula to determine the rate corrected QT interval (QTc):

QTc = Measured QT interval / %Preceding R-R interval

In fewer formal terms, divide the measured QT interval by the square root of the R-R interval immediately preceding.

Figure 5: Calculation of the rate corrected QT interval, the QTc

The normal QTc is less than 0.42 msec. However, there is considerable overlap between normal persons and those with low-grade pathologic increases in their QTc. Most experts consider QTc values of 0.46 - 0.48 msec borderline abnormal, between 0.48 - 0.50 msec moderately abnormal, and > 0.50 msec definitely abnormal.

The broader question is whether or not all individuals, symptomatic or not, should receive a screening EKG. This is currently the topic of heated debate between those who advocate routine EKGs early in life, and those who argue that EKGs are not cost-effective in saving lives. Some experts suggest that all newborns should receive a screening EKG to look for LQTS, as well as other congenital EKG abnormalities (e.g., Brugada’s Syndrome) within the first week of life.

It is this writers’ opinion that every person should have a screening EKG, interpreted by a qualified reader, by age eight, as well as a “cardiovascular screen” consisting of a standard heart exam and the following questions:

• Have you ever passed out or become dizzy during or after exercise?
• Have you ever had chest pain during or after exercise?
• Do you get tired more quickly than your friends do during exercise?
• Have you had high blood pressure or high cholesterol?
• Have you ever been told that you had a heart murmur?
• Has any family member or relative died of heart problems or sudden death before age 50?
• Have you had a severe viral infection such as mononucleosis or myocarditis within the last month?
• Has a physician ever denied or restricted your participation in sports for any heart problem?
• Have any of your relatives ever had any of the following conditions?
i. Hypertrophic cardiomyopathy
ii. Dilated cardiomyopathy
iii. Marfan’s syndrome
iv. Long QT syndrome
v. Significant heart arrhythmia
vi. Any other type of heart disease?

An abnormality on the EKG or heart exam, or positive answers to any of the above questions indicates the need for further evaluation. Though far from 100% accurate, the above cardiovascular screen would identify 50-75% of at-risk individuals.