The PR interval is said to be the time from the starting of a P wave to begin the QRS complex. Shortened PR interval ranges 120 ms whereas; the normal range of PR intervals is 120 to 200 ms. Two associated conditions that are linked with shortened PR intervals at the time of resting ECG are pre-excitation syndrome and junctional arrhythmia (Bay et al. 2020). Examples of pre-excitation syndrome are Wolff-Parkinson-White (WPW) and Lown-Ganong-Levine (LGL) syndromes. On the contrary, junctional arrhythmia can be exemplified as atrioventricular reentrant tachycardia or the junctional rhythm.
Pathophysiological conditions of WPW include the presence of an alternative pathway that connects ventricles and atria. As per the opinion of Borloz (2020), impulses produced by this pathway are faster than the normal impulses and produce a shortened PR interval. Electrocardiographic characteristic of this condition involves broad QRS and delta waves implying a slurred upstroke to the QRS complex.
QT interval is termed to be measured from the starting of the QRS complex till the end of the T wave. It is represented as the amount of time consumed in the ventricular depolarisation and repolarization. As per the discussions of Meek and Morris (2002), normal range of QT intervals can be suggested as 0.35 to 0.45 seconds. An increase more than half of the interval between two adjacent R waved (R-R interval) is considered as abnormal. Measurement of QT intervals is important as a prolonged interval can be noticed in case of slow rate of the heart. However, aging of an individual is associated with increased QT intervals to some extent and a particular trend is observed in case of these intervals as well (Chorin et al. 2020). According to this trend, women are seen to experience longer QT intervals in comparison to males.
Measurement of this interval relies on Bazett’s correction and the equation can be given as below:
The review article is based on the abnormal ventilatory responses of the patients with chronic heart failure to exercises or peak oxygen consumption. Findings of this article shows that-Question 4
Heart rate is observed to increase in response to exercises and central withdrawal of parasympathetic inhibition and increase in sympathetic tone are responsible for this. Further increase of heart rate is associated with increment of sympathetic stimulation in the central nervous system and circulating catecholamine. As per the perspectives of Kligfield and Lauer (2006), chronotropic incompetence is defined as the condition where heart rate does not increase with physical exercise. It is determined that chronotropic incompetence can lead to various cardiac events such as all-cause mortality.
Cardiac axis is referred to as the mean direction of waves related to ventricular depolarization on a vertical plane and it is measured from a referencing point considered as zero. Measurement of cardiac axis is done with various methods and the most prevalent method is inspection of three leads called lead I, II and III. These methods can be described as below:
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