The QT intervalA period measured on rhythm strip paper that measures a wave and a segment; the distance measured is equal to time taken as an ECG is voltage over time; a PR interval for example is measured from the beginning of... represents a complete ventricular cycle of depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... and repolarizationFollows depolarization, involving the return to a pre-depolarization state; the myocardial cell’s electrical potential returns from +30 mV to its polarized state of –90 mV; the ions potassium, calcium and sodium are largely involved; note that contraction of the myocardial.... The QT interval is measured from the beginning of the QRS complexThe electrical representation of ventricular depolarization; the atrial repolarization is also a part of the QRS. ECG interpretation relies heavily on the QRS complex. The QRS complex represents the depolarization of the ventricles. The repolarization of the atria is also... to the end of the T waveThe wave that arrives after the QRS; is a graphical presentation of ventricular repolarization. Expect a T wave to follow every QRS complex. The T wave is a graphic representation of the repolarization of the ventricle. The T wave is.... A QT interval should be less than 1/2 the R-R intervalThe distance between the top of the R waves. Figure 4.15 The Normal Q Wave and QT Interval Figure 4.15 illustrates the Q wave, QT interval and the R-R interval. A normal QT interval should be less than half the....
The time taken from the beginning of ventricular depolarizationThe depolarization of the myocardium is represented on an ECG by a series of waveforms, one for atrial depolarization and soon after a larger waveform for ventricular depolarization. Normal ventricular depolarization begins with the septal fascicle of the left bundle... to the end of ventricular repolarizationThe T wave is a graphic representation of the repolarization of the ventricle. The T wave is typically about 0.10 to 0.25 seconds wide with an amplitude less than 5 mm. While ventricular depolarization occurs rapidly producing a tall QRS...; this interval begins with the onset of the QRS to the end of the T wave; a normal QT interval should be less than or equal to half the R-R interval; note that long QT intervals are associated with increased incidence of R-on-T phenomena and resulting episodes of ventricular tachycardiaIs a cardiac rhythm characterized by rapidly occurring wide QRS complexes with absent or infrequent P waves evident; the absence of atrial kick, the lack of filling time, and the tendency for ventricular tachycardia to change to ventricular fibrillation makes... or ventricular fibrillationA chaotic unorganized cardiac rhythm with several firing regions within the ventricles; the result is uncoordinated ventricular activity and NO cardiac output – a lethal dysrhythmia; fine ventricular fibrillation defines an amplitude less than 3 mm; coarse ventricular fibrillation has....
A long QT intervalA long QT interval, wider than 1/2 the R-R interval, is a significant risk factor for developing hemodynamically unstable dysrhythmias such as ventricular tachycardia and torsades de pointes. A prolonged QT interval is also associated with a higher incidence of... wider than 1/2 the R-R interval is a significant risk factor for developing hemodynamically unstable dysrhythmiasUsed interchangeably with arrhythmia, refers to any abnormal rhythm – not normal sinus rhythm or sinus tachycardia. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 such as ventricular tachycardiaA cardiac rhythm with a rate above 100/minute; for example, if the impulse originates from the atria with a rate of 160/minute, the rhythm is called an atrial tachycardia. A cardiac rhythm is usually named first by the location of... and torsades de pointesMeans the twisting of the points, a polymorphic ventricular tachycardia characterized by periods of increasing QRS amplitude followed with a period of reduced QRS amplitude – then the pattern repeats again; often associated with effects of cardiac drugs or with.... A prolonged QT interval is also associated with a higher incidence of sudden death.
The concern around a longer QT interval centers around the possibility of the next QRS coming at the tail end of the T wave, called an R-on-T phenomenon. This phenomenon can potentially cause dangerous dysrhythmias such as torsades de pointes. Causes of prolonged QT intervals include long QT syndrome, antiarrythmics such as quinidine and procainamide, tricyclic antidepressants, and hypokalemiaBlood potassium level lower than normal limits. Table 6.5 Normal and Abnormal Characteristics of ECG Waveforms Table 6.5 provides a non-exhaustive list of cardiac conditions that are associated with a variety of abnormal ECG waveforms. Arriving at a useful interpretation....
Figure 4.15 illustrates the Q waveA Q wave is the first negative deflection of the QRS complex that is not preceded by a R wave. A normal Q wave is narrow and small in amplitude. Note that a wide and/or deep Q wave may signify..., QT interval and the R-R interval. A normal QT interval should be less than half the R-R interval. A prolonged QT interval is associated with increased risk of R-on-T triggered lethal dysrhythmias.
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 83, 85-86