Qt qtc in ecg normal range

CORRECTING THE QT INTERVAL The corrected QT interval (QTc) should be calculated. However, this should not be done when the patient is in tachycardia or bradycardia (using long-term electrocardiographic monitoring or beta-blockers if needed) to prevent the use of the Bazett formula at heart rates in which its correction is not linear and may lead to overestimation or underestimation of QTc values. Proposed diagnostic criteria for short QT syndrome The threshold of 360 ms is considered diagnostic of short QT syndrome if it is accompanied by 1 or more of the following: • Pathogenic mutation • Family history of short QT syndrome • Family history of sudden death before age 40 • Survival of an episode of ventricular tachycardia-ventricular fibrillation (VT-VF) in the absence of heart disease. Most experts agree that even without any of these factors, a QTc shorter than 330 to 340 ms is diagnostic of short QT syndrome, as such values are very rare in a healthy population. Assess for acquired causes first Acquired causes of short QT interval should be considered first. Potential causes of nongenetic QT shortening include: • Hypercalcemia, hyperkalemia, acidosis, and hyperthermia • Drug effects, eg, from digitalis, • Effect of acetylcholine and increased vagal tone, through activation of acetylcholine-sensitive potassium channels. This leads to deceleration-dependent shortening of the QT interval (ie, paradoxical QT interval shortening with a decrease in heart rate instead of lengt...

The QT interval, long QT syndrome (LQTS) & ventricular arrhythmias (torsade de pointes) due to prolonged QT interval The QT interval is the time interval from the beginning of the QRS complex to the end of the T-wave. This interval represents the total time taken to depolarize and repolarize the ventricles ( Figure 1). The length of the QTinterval correlates strongly with the risk of potentially life-threatening ventricular arrhythmias. Therefore, the QT interval must always be assessedwhen interpreting the Long QT syndrome (LQTS)is manifest when a long QT interval induces ventricular arrhythmias. Figure 1. The QT interval on the ECG. The QT intervalis inversely related to heart rate. As the heart rate increases, the QT interval decreases and vice versa. The physiological purpose of this phenomenon is to allow for faster cardiac cycles during tachycardia (e.g during physical exertion). Therefore, to judge whether the QT interval is normal or not, one must adjust for the current heart rate. This is done by adjusting the QT interval for the heart rate, and the resulting QT interval is referred to as corrected QT interval, or simply QTc interval. The primary hazard lies in long QTc intervals, because they induce a very unstablepolymorphic torsade de pointes. Abnormally short QTc interval is also arrhythmogenic but it is a very rare condition. Several formulas have been suggested to calculate corrected QT intervals.Some of these formulas follow: Bazett’s formula for calculatin...

• Causes of Prolonged QT Interval • Congenital • Congenital Long QT Syndrome (LQTS) • Jervel and Lange-Nielsen syndrome • Drugs • Antiarrhythmics - amiodarone, sotalol, procainamide, quinidine • Antidepressants - amitryptiline, dothiapine, citalopram, escitalopram • Antipsychotics - risperidone, haloperidol, clozapine, droperidol, chlorpromazine • Antiemetics - ondansetron, domperidone • Macrolides - azithromycin, clarithromycin, erythromycin • Quinolones - ciprofloxacin, moxifloxacin • Antifungals - fluconazole, ketoconazole • Antimalarials - chloroquine, mefloquine • Anaesthetic gases - halothane, sevoflurane • Methadone • Other • Hypokalaemia • Hypomagnesaemia • Hypocalcaemia • Severe hypothermia • Severe bradycardia- sick sinus syndrome, complete heart block • Cardiovascular disease- tako-tsubo cardiomyopathy, MI, CCF • Cerebrovascular disease- intracranial / subarachnoid haemorrhage, stroke • Hypothyroidism The congenital long QT syndromes are a diverse group of diseases that predispose to ventricular tachyarrhythmias. The three most common are LQTS1, in which events are triggered by exercise; LQTS2, in which events are triggered by stress and loud noises; and LQTS3, in which events often occur during sleep. Other congenital causes are much rarer.

CORRECTING THE QT INTERVAL The corrected QT interval (QTc) should be calculated. However, this should not be done when the patient is in tachycardia or bradycardia (using long-term electrocardiographic monitoring or beta-blockers if needed) to prevent the use of the Bazett formula at heart rates in which its correction is not linear and may lead to overestimation or underestimation of QTc values. Proposed diagnostic criteria for short QT syndrome The threshold of 360 ms is considered diagnostic of short QT syndrome if it is accompanied by 1 or more of the following: • Pathogenic mutation • Family history of short QT syndrome • Family history of sudden death before age 40 • Survival of an episode of ventricular tachycardia-ventricular fibrillation (VT-VF) in the absence of heart disease. Most experts agree that even without any of these factors, a QTc shorter than 330 to 340 ms is diagnostic of short QT syndrome, as such values are very rare in a healthy population. Assess for acquired causes first Acquired causes of short QT interval should be considered first. Potential causes of nongenetic QT shortening include: • Hypercalcemia, hyperkalemia, acidosis, and hyperthermia • Drug effects, eg, from digitalis, • Effect of acetylcholine and increased vagal tone, through activation of acetylcholine-sensitive potassium channels. This leads to deceleration-dependent shortening of the QT interval (ie, paradoxical QT interval shortening with a decrease in heart rate instead of lengt...

Checklist Assess ventricular (RR intervals) and atrial (PP intervals) rate and rhythm: • Is ventricular rhythm regular? What is the ventricular rate (beats/min)? • Is atrial rhythm regular? What is the atrial rate (beats/min)? • P-waves should precede every QRS complex and the P-wave should be positive in lead II. Common findings • Sinus rhythm (which is the normal rhythm) has the following characteristics: (1) heart rate 50–100 beats per minute; (2) P-wave precedes every QRS complex; (3) the P-wave is positive in lead II and (4) the PR interval is constant. • Causes of bradycardia: sinus bradycardia, sinoatrial block, sinoatrial arrest/inhibition, second-degree AV block, third-degree AV block. Note that escape rhythms may arise during bradycardia. Also note that bradycardia due to dysfunction in the sinoatrial node is referred to as sinus node dysfunction (SND). If a person with ECG signs of SND is symptomatic, the condition is classified as sick sinus syndrome (SSS). • Causes of tachycardia (tachyarrhythmia) with narrow QRS complexes (QRS duration <0,12 s): sinus tachycardia, inappropriate sinus tachycardia, sinoatrial re-entry tachycardia, atrial fibrillation, atrial flutter, atrial tachycardia, multifocal atrial tachycardia, AVNRT, AVRT (pre-excitation, WPW). Note that narrow complex tachyarrhythmia rarely cause circulatory compromise or collapse. • Causes of tachycardia (tachyarrhythmia) with wide QRS complexes (QRS duration ≥0,12 s): ventricular tachycardia is the mo...

• Causes of Prolonged QT Interval • Congenital • Congenital Long QT Syndrome (LQTS) • Jervel and Lange-Nielsen syndrome • Drugs • Antiarrhythmics - amiodarone, sotalol, procainamide, quinidine • Antidepressants - amitryptiline, dothiapine, citalopram, escitalopram • Antipsychotics - risperidone, haloperidol, clozapine, droperidol, chlorpromazine • Antiemetics - ondansetron, domperidone • Macrolides - azithromycin, clarithromycin, erythromycin • Quinolones - ciprofloxacin, moxifloxacin • Antifungals - fluconazole, ketoconazole • Antimalarials - chloroquine, mefloquine • Anaesthetic gases - halothane, sevoflurane • Methadone • Other • Hypokalaemia • Hypomagnesaemia • Hypocalcaemia • Severe hypothermia • Severe bradycardia- sick sinus syndrome, complete heart block • Cardiovascular disease- tako-tsubo cardiomyopathy, MI, CCF • Cerebrovascular disease- intracranial / subarachnoid haemorrhage, stroke • Hypothyroidism The congenital long QT syndromes are a diverse group of diseases that predispose to ventricular tachyarrhythmias. The three most common are LQTS1, in which events are triggered by exercise; LQTS2, in which events are triggered by stress and loud noises; and LQTS3, in which events often occur during sleep. Other congenital causes are much rarer.

The QT interval, long QT syndrome (LQTS) & ventricular arrhythmias (torsade de pointes) due to prolonged QT interval The QT interval is the time interval from the beginning of the QRS complex to the end of the T-wave. This interval represents the total time taken to depolarize and repolarize the ventricles ( Figure 1). The length of the QTinterval correlates strongly with the risk of potentially life-threatening ventricular arrhythmias. Therefore, the QT interval must always be assessedwhen interpreting the Long QT syndrome (LQTS)is manifest when a long QT interval induces ventricular arrhythmias. Figure 1. The QT interval on the ECG. The QT intervalis inversely related to heart rate. As the heart rate increases, the QT interval decreases and vice versa. The physiological purpose of this phenomenon is to allow for faster cardiac cycles during tachycardia (e.g during physical exertion). Therefore, to judge whether the QT interval is normal or not, one must adjust for the current heart rate. This is done by adjusting the QT interval for the heart rate, and the resulting QT interval is referred to as corrected QT interval, or simply QTc interval. The primary hazard lies in long QTc intervals, because they induce a very unstablepolymorphic torsade de pointes. Abnormally short QTc interval is also arrhythmogenic but it is a very rare condition. Several formulas have been suggested to calculate corrected QT intervals.Some of these formulas follow: Bazett’s formula for calculatin...