ECG Basic Principles Flashcard 3

A. Rationale: Lead II is the monitoring lead, which is the one usually displayed in cardiac monitors. This gives healthcare professionals a quick assessment of the patient’s overall cardiac electrical pattern.

D. Rationale: The U wave follows the T wave of ventricular repolarization and may not always be observed due to its small size. U waves are thought to represent repolarization of the Purkinje fibers.

Answer choice A – The P wave represents atrial depolarization.
Answer voice B – The QRS complex represents ventricular depolarization.
Answer choice C – The T wave represents ventricular repolarization.

B. Rationale: Depolarization is essential to the function of cardiac myocytes and constitutes an excitatory state that allows for an action potential to occur and transmit impulses.

Answer choice A – Repolarization restores the charge differences between the internal and external cell membrane following depolarization.
Answer choice C – Calcium influx, or an increase in intracellular calcium, occurs during cellular depolarization.
Answer choice D – Na+ efflux, or a decrease in intracellular Na+, occurs during cellular repolarization.

B. Rationale: The junctional escape rhythm is a failsafe mechanism rather than an arrhythmia formed due to an irritable atrial focus or SA node. It has an inherent rate of 40–60 bpm, which is the next fastest inherent rate that the heart’s conduction system resorts to when the SA node is ineffective.

A. Rationale: The P wave represents right atrial depolarization followed by left atrial depolarization. It is a low positive deflection. The presence of the P wave makes the ECG rhythm sinus in origin. The T and U waves are part of ventricular depolarization.