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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.

A. The P wave

B. The QRS duration

C. The T wave

D. The U wave

E. The PR interval

Which of the following normally has a slowly depolarizing “prepotential”?

A. Sinoatrial node

B. Atrial muscle cells

C. Bundle of His

D. Purkinje fibers

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?

A. Na+ channels

B. Cl channels

C. Ca2+ channels

D. K+ channels

E. HCO3− channels


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