cardiovascular

Determine which of the following electrocardiogram (ECG) tracings is missing P waves but is otherwise regular.

• A

• B

• C

• D

Answer explanation

B illustrates a QRS complex and a T wave, but it is missing the P wave.

What causes heart sounds?

• opening of heart valves

• heart valve closure

• pressure of blood in the ventricles

• blood flowing from the atria into the ventricles

Answer explanation

Heart sounds are caused by heart valve closure.

 Increasing end-diastolic volume (EDV) and end-systolic volume (ESV) will increase stroke volume.

• TRUE

• FALSE

Answer explanation

Stroke volume (the volume of blood ejected from the ventricle during systole) is equal to the difference between EDV (the volume of blood in the ventricle before it contracts) and ESV (the volume of blood remaining in the ventricle after it contracts). Increasing EDV will result in a larger stroke volume; however, increasing ESV will result in a smaller stroke volume.

What does the QRS wave of the electrocardiogram (ECG) represent?

• atrial depolarization

• atrial repolarization

• ventricular depolarization

• ventricular repolarization

Answer explanation

Ventricular depolarization is represented by the QRS complex of an ECG.

As soon as ventricular pressure falls below atrial pressure, the atrioventricular valve will open and ventricular filling will begin.

• TRUE

• FALSE

Answer explanation

At any given time, the pressures on either side of a heart valve determine whether a valve is open or closed. During ventricular systole, pressure in the ventricle increases. As soon as ventricular pressure rises above atrial pressure, the AV valve closes. During ventricular diastole, pressure in the ventricle decreases. As soon as ventricular pressure drops below atrial pressure, the AV valve opens, and ventricular filling begins.

Which of the following terms is correctly matched to its description?

• ventricular diastole: period of ventricular contraction

• atrial systole: period of atrial relaxation

• quiescent period: period of total heart relaxation

• stroke volume: amount of blood pumped out by each ventricle in one minute

Answer explanation

During each cardiac cycle there is a period of time in which both the atria and ventricles are relaxed (in diastole) at the same time; this is called the quiescent period.

What separates the parietal and visceral pericardium?

• epicardium

• fibrous pericardium

• myocardium

• pericardial cavity

Answer explanation

The pericardial cavity separates the parietal and visceral pericardium. This cavity contains serous fluid that lubricates the visceral and parietal membranes.

Which of the following descriptions of cardiac pacemaker cells is INCORRECT?

• The rapid depolarization phase of the pacemaker cell action potential is due to Na⁺ influx through Na⁺ channels.

• The pacemaker cells of the sinoatrial (SA) node exhibit the fastest rate of spontaneous depolarization.

• The pacemaker cells of the atrioventricular (AV) node are smaller and have fewer gap junctions compared to the rest of the conduction system.

• Cutting the vagus nerve would allow the pacemaker cells of the sinoatrial (SA) node to generate action potentials at a faster rate.

Answer explanation

The action potential begins with a slow depolarization towards threshold, called the pacemaker potential (or prepotential). At threshold (approximately -40 mV), Ca²⁺ channels open, allowing explosive entry of Ca²⁺ from the extracellular space. As a result, in pacemaker cells, it is the influx of Ca²⁺ (rather than Na⁺) that produces the rapid depolarization phase of the action potential.

Electrical impulses pass through the conduction system of the heart in the following sequence:

• SA node, AV node, bundle of His, bundle branches, and Purkinje fibers

• SA node, bundle branches, AV node, bundle of His, and Purkin

• SA node, bundle of His, AV node, bundle branches, and Purkinje fibers

• SA node, bundle branches, bundle of His, AV node, and Purkinje fibers

Answer explanation

The impulses of the heart originate at the SA node (pacemaker). The impulse is then transmitted to the AV node (atrioventricular node), where the impulse slows down to allow the atria to completely contract and thereby fill the adjacent ventricles. The AV node then transmits the impulse to the bundle of His, which branches into left and right bundle branches. The bundle branches give rise to the Purkinje fibers, which transmit the impulse to the ventricle walls and stimulate ventricular contraction.

Which portion of the electrocardiogram represents the wave-like change in charge in the positive direction received by the atria from the sinoatrial (SA) node?

• T wave

• S-T segment

• P wave

• QRS complex

Answer explanation

The P wave represents the depolarization of the left and right atria and the beginning of atrial systole.