Question 1

An ECG machine's sensitivity must be calibrated so that a 1-mV electrical signal will produce a deflection measuring exactly _____-mm tall.

Accepted Answer

The ECG machine's sensitivity must be calibrated so that a 1-mV electrical signal will produce a deflection that measures exactly 10-mm tall. When properly calibrated, a small box is 1-mm high (i.e., 0.1 mV), and a large box, which is equal to five small boxes, is 5 mm high (i.e., 0.5 mV).

Question 2

The inferior surface of the left ventricle is supplied by the _____ coronary artery in most of the population.

Accepted Answer

A branch of the RCA supplies the inferior surface of the left ventricle in approximately 85% of individuals.

Question 3

_____ is a term used to describe the period of recovery that cells need after being discharged before they are able to respond to a stimulus.

Accepted Answer

Refractoriness is a term used to describe the period of recovery that cells need after being discharged before they are able to respond to a stimulus.

Question 4

In an adult, the normal duration of the QRS complex is _____ seconds.

Accepted Answer

The beginning of the QRS is measured from the point where the first wave of the complex begins to deviate from the baseline. The point at which the last wave of the complex begins to level out at, above, or below the baseline marks the end of the QRS complex. The QRS is considered narrow (i.e., normal) if it measures 0.11 second or less; it is considered wide if it measures more than 0.11 second. A QRS complex of 0.11 second or less (i.e., narrow) is presumed to be supraventricular in origin.

Question 5

Atrial fibrillation is characterized by _____.

Accepted Answer

Atrial fibrillation (AFib) is characterized by an erratic, wavy baseline and an irregularly irregular ventricular rhythm. Because of the quivering of the atrial muscle and because there is no uniform wave of atrial depolarization in AFib, there is no P wave. Instead, you see wavy deflections that are called "fibrillatory waves."

Question 6

Two conditions must exist to suspect bundle branch block. First, the QRS complex must have an abnormal duration (0.12 second or more in width), and second _____.

Accepted Answer

Essentially two conditions must exist to suspect bundle branch block. First, the QRS complex must have an abnormal duration (i.e., 0.12 second or more in width if a complete BBB). Second, the QRS complex must arise as the result of supraventricular activity, excluding ventricular beats. If these two conditions are met, delayed ventricular conduction is assumed to be present, and bundle branch block is the most common cause of this abnormal conduction.

Question 7

Which of the following correctly describes multifocal atrial tachycardia?

Accepted Answer

With multifocal atrial tachycardia, the atrial and ventricular rhythms are usually irregular as the pacemaker site shifts from the SA node to ectopic atrial locations or AV junction.

Question 8

Which of the following are chest leads?

Accepted Answer

The chest leads are identified as V₁, V₂, V₃, V₄, V₅, and V₆. Each electrode placed in a V position is a positive electrode, measuring electrical potential with respect to the Wilson central terminal.

Question 9

Where is the positive electrode placed in lead III?

Accepted Answer

Lead III records the difference in electrical potential between the left leg (+) and left arm (-) electrodes. In lead III, the positive electrode is placed on the left leg and the negative electrode is placed on the left arm.

Question 10

In a junctional rhythm viewed in lead II, where is the location of the P wave on the ECG if ventricular depolarization precedes atrial depolarization?

Accepted Answer

If the AV junction paces the heart, the electrical impulse must travel in a backward (retrograde) direction to activate the atria. If the atria depolarize before the ventricles, an inverted P wave will be seen before the QRS complex and the PR interval will usually measure 0.12 second or less. The PR interval is shorter than usual because an impulse that begins in the AV junction does not have to travel as far to stimulate the ventricles. If the atria and ventricles depolarize at the same time, a P wave will not be visible because it will be hidden in the QRS complex. When the atria are depolarized after the ventricles, the P wave typically distorts the end of the QRS complex and an inverted P wave will appear after the QRS.

Question 11

Anterior wall myocardial infarctions are most often a result of an occlusion of a branch of the _____ coronary artery.

Accepted Answer

Anterior myocardial infarctions are usually the result of an occlusion of the diagonal branch of the left anterior descending coronary artery, which is a branch of the left coronary artery.

Question 12

Which of the following correctly reflects the ECG indicators of ischemia?

Accepted Answer

In a patient experiencing an acute coronary syndrome, T-wave inversion, which can occur simultaneously with ST-segment elevation, suggests the presence of myocardial ischemia. The development of pathologic Q waves provides evidence that tissue death has occurred. A pathologic Q wave indicates the presence of dead myocardial tissue and subsequently, a loss of electrical activity.

Question 13

On an ECG, what is the first negative deflection seen after the P wave?

Accepted Answer

The Q wave is the first negative deflection seen after the P wave.

Question 14

The _____ originate from small mounds of myocardium called papillary muscles and serve as anchors to prevent the cusps of the AV valves from inverting into the atria.

Accepted Answer

Chordae tendineae are thin strands of connective tissue. On one end, they are attached to the underside of the AV valves. On the other end, they are attached to small mounds of myocardium called papillary muscles. Papillary muscles project inward from the lower portion of the ventricular walls. When the ventricles contract and relax, so do the papillary muscles. The papillary muscles adjust their tension on the chordae tendineae, preventing them from bulging too far into the atria.

Question 15

Which of the following leads are anatomically contiguous?

Accepted Answer

Two leads are contiguous if they look at the same or adjacent areas of the heart or they are numerically consecutive chest leads. Leads V₂, V₃, V₄ are numerically consecutive chest leads.

Question 16

Signs and symptoms experienced during a tachydysrhythmia are usually primarily related to _____.

Accepted Answer

In a patient with coronary artery disease, sinus tachycardia can cause problems. The heart's demand for oxygen increases as the heart rate increases. As the heart rate increases, there is less time for the ventricles to fill and less blood for the ventricles to pump out with each contraction, which can lead to decreased cardiac output. Because the coronary arteries fill when the ventricles are at rest, rapid heart rates decrease the time available for coronary artery filling. This decreases the heart's blood supply. Chest discomfort can result if the supplies of blood and oxygen to the heart are inadequate.

Question 17

Which side of the heart is a high-pressure system that pumps arterial blood to the systemic circulation?

Accepted Answer

The job of the left heart is to receive oxygenated blood from the lungs and pumps it out to the rest of the body (i.e., the systemic circulation). The left side of the heart is a high-pressure pump. The pressure within the left atrium is normally between 8 and 12 mm Hg. Blood is carried from the heart to the organs of the body through arteries, arterioles, and capillaries. Blood is returned to the right heart through venules and veins.

Question 18

The myocardium is thickest in the ____.

Accepted Answer

The wall of the left ventricle is threefold thicker than that of the right because the left ventricle propels blood to most vessels of the body. The right ventricle moves blood only through the blood vessels of the lungs and then into the left atrium.

Question 19

The left atrium receives blood from the _____.

Accepted Answer

The left atrium receives freshly oxygenated blood from the lungs via the right and left pulmonary veins.

Question 20

A delta wave is an ECG characteristic associated with which of the following dysrhythmias?

Accepted Answer

Characteristic ECG findings in Wolff-Parkinson-White syndrome include a short PR interval, QRS widening, and a delta wave. A delta wave is an initial slurred deflection at the beginning of the QRS complex that results from the initial activation of the QRS by conduction over the accessory pathway.

Quiz 10: Posttest