cardiovascular disorders
Torsades de Pointes Ventricular Tachycardia
Diagnosis of Torsades de Pointes Ventricular Tachycardia
Electrocardiography (ECG) Diagnosis is by ECG showing an undulating QRS axis, with the polarity of complexes shifting around the baseline (see figure Torsades de pointes ventricular tachycardia ). ECG between episodes shows a long QT interval after correction for heart rate (QTc). Normal QTc values are about 0.40 second for men and 0.41 second for women and are considered prolonged when > 0.47 second for men or > 0.48 second for women. A family history may suggest a congenital syndrome. ECG warning signsof impending TdeP VT other than prolongation of the QT interval include T-wave and U-wave fusion (sometimes with giant TU waves) Post-extrasystolic changes in repolarization pattern Macroscopic T-wave alternans (visible alternation of two different appearing T-waves) Frequent polymorphic ventricular premature beats representing single beats of TdeP (often in bigeminy) Repetitive short runs of polymorphic ventricular tachycardia The TdeP VT itself is a rapid, polymorphic VT that tends to self-terminate. Onset typically follows a short-long-short RR interval initiation sequence (although this sequence is not specific for TdeP VT): The first short RR interval is between a baseline beat (usually a normal beat) and a premature beat (usually a premature ventricular beat). The long RR interval is the post-extrasystolic pause and ends with a baseline beat (usually a normal beat). The pause further prolongs the QT interval of this baseline beat and it is followed by a short RR interval when the TdeP VT begins. Although patients may have a normal QTc at other times, the QTc is usually substantially prolonged around the time of TdeP VT and the QT interval of the last QRS complex prior to TdeP VT must be long (often with a giant TU wave). Torsades de pointe ventricular tachycardia typically follows a short-long-short RR interval initiation sequence and the QT interval of the last QRS complex prior to TdeP VT must be long. 