Chapter 29. Origin of the Heartbeat & the Electrical Activity of the Heart
Which part of the ECG (eg, Figure 29–5) corresponds to ventricular repolarization?
Figure 29-5. Waves of the ECG. Standard names for individual waves and segments that make up the ECG are shown. Electrical activity that contributes the observed deflections are discussed in the text and in Table 29–2. ECG, electrocardiogram.
Table 29–2. ECG intervals. ||Download (.pdf) Table 29–2. ECG intervals.
| ||Normal Durations (second, s) || |
| Intervals ||Average ||Range ||Events in the Heart during Interval |
|PR intervala ||0.18b ||0.12–0.20 ||Atrioventricular conduction |
|QRS duration ||0.08 ||to 0.10 ||Ventricular depolarization |
|QT interval ||0.40c ||to 0.43 ||Ventricular action potential |
|ST interval (QT minus QRS) ||0.32 ||… ||Plateau portion of the ventricular action potential |
Which of the following normally has a slowly depolarizing “prepotential”?
E. Ventricular muscle cells
In second-degree heart block
A. the ventricular rate is lower than the atrial rate.
B. the ventricular ECG complexes are distorted.
C. there is a high incidence of ventricular tachycardia.
D. stroke volume is decreased.
E. cardiac output is increased.
Currents caused by opening of which of the following channels contribute to the repolarization phase of the action potential of ventricular muscle fibers?