CSLB General Building (B) — All Questions

What is the inherent firing rate of the sinoatrial node in a healthy adult?

• a.20 to 40 beats per minute
• b.40 to 60 beats per minute
• c.60 to 100 beats per minute✓
• d.100 to 150 beats per minute

The SA node in the upper right atrium is the heart's primary pacemaker and fires 60 to 100 times per minute, which is why normal sinus rhythm is defined by that range. The AV junction fires at 40 to 60 as a backup, and the Purkinje network fires at 20 to 40 as the last resort. A rate of 100 to 150 is a tachycardia, not an inherent pacemaker rate.

A patient's SA node fails completely. Which structure normally takes over, and at what rate?

• a.The Purkinje fibers at 60 to 100 beats per minute
• b.The AV junction at 40 to 60 beats per minute✓
• c.The bundle branches at 100 to 120 beats per minute
• d.The atrial muscle at 20 to 40 beats per minute

The AV junction is the secondary pacemaker and assumes control at 40 to 60 beats per minute when the SA node fails, producing a junctional escape rhythm with absent or inverted P waves. The Purkinje network fires only at 20 to 40 and takes over if the junction also fails. Bundle branches conduct rather than pace at a fast rate, and general atrial muscle is not a designated escape pacemaker.

What is the inherent rate of the Purkinje fibers, and what does a rhythm at that rate look like?

• a.60 to 100 beats per minute with narrow complexes
• b.40 to 60 beats per minute with inverted P waves
• c.100 to 150 beats per minute with sawtooth waves
• d.20 to 40 beats per minute with wide QRS complexes and no P waves✓

The Purkinje network is the heart's pacemaker of last resort at 20 to 40 beats per minute, and because the impulse starts below the AV junction, the QRS is wide and no P waves precede it. The 60 to 100 range belongs to the SA node and produces narrow complexes with upright P waves. The 40 to 60 range with inverted P waves describes a junctional rhythm, and sawtooth waves indicate atrial flutter.

What is the correct order of the cardiac electrical conduction pathway?

• a.SA node, AV node, bundle of His, right and left bundle branches, Purkinje fibers✓
• b.AV node, SA node, Purkinje fibers, bundle of His, bundle branches
• c.SA node, bundle of His, AV node, Purkinje fibers, bundle branches
• d.Purkinje fibers, bundle branches, bundle of His, AV node, SA node

The impulse begins in the SA node, spreads across the atria to the AV node, passes through the bundle of His, splits into the right and left bundle branches, and ends in the Purkinje fibers that depolarize the ventricular muscle. Any sequence that starts at the AV node or the Purkinje fibers reverses normal physiology, and the bundle of His always lies below the AV node, never above it.

Why does the impulse pause briefly at the AV node, and how does that pause appear on the EKG?

• a.To let the ventricles repolarize; it appears as the T wave
• b.To let the coronary arteries fill; it appears as the QT interval
• c.To let the atria finish contracting and fill the ventricles; it appears as the flat segment of the PR interval✓
• d.To slow the SA node; it appears as the ST segment

The AV node delays the impulse about a tenth of a second so the atria can complete their contraction and top off ventricular filling before the ventricles fire, and that delay is the flat portion of the PR interval between the end of the P wave and the start of the QRS. The T wave represents ventricular repolarization. The ST segment is the interval between depolarization and repolarization of the ventricles, and the AV node does not regulate the SA node.

What is depolarization?

• a.The relaxation of cardiac muscle as it returns to its resting state
• b.The electrical discharge of cardiac cells that stimulates contraction✓
• c.The flow of blood into the coronary arteries
• d.The closing of the atrioventricular valves

Depolarization is the rapid electrical change across the cell membrane that triggers mechanical contraction, and it produces the P wave in the atria and the QRS complex in the ventricles. Relaxation and electrical recovery are repolarization. Coronary filling and valve closure are mechanical events of the cardiac cycle, not the electrical activity the EKG records.

A student asks why an EKG can look normal in a patient whose heart is not pumping effectively. What is the best explanation?

• a.The EKG measures blood pressure, not electrical activity
• b.The EKG only records the atria
• c.EKG machines are frequently inaccurate
• d.The EKG records electrical activity, and electrical activity can be present without effective mechanical contraction✓

An EKG records only the electrical events of the heart, so an organized rhythm can appear on the monitor while the heart produces no pulse, a situation known as pulseless electrical activity. This is exactly why the technician always confirms the patient's condition rather than treating the monitor. The EKG does not measure pressure or output, and it records both atrial and ventricular activity.

What is the correct path of blood through the heart, starting with deoxygenated blood returning from the body?

• a.Right atrium, tricuspid valve, right ventricle, pulmonic valve, lungs, left atrium, mitral valve, left ventricle, aorta✓
• b.Left atrium, mitral valve, left ventricle, lungs, right atrium, tricuspid valve, right ventricle, aorta
• c.Right atrium, mitral valve, right ventricle, aorta, lungs, left atrium, tricuspid valve, left ventricle
• d.Right ventricle, right atrium, lungs, left ventricle, left atrium, aorta

Deoxygenated blood enters the right atrium from the venae cavae, passes the tricuspid valve into the right ventricle, leaves through the pulmonic valve to the lungs, returns oxygenated to the left atrium, crosses the mitral valve into the left ventricle, and exits through the aortic valve to the body. The mitral valve is always on the left and the tricuspid on the right, and blood always flows atrium to ventricle, never the reverse.

Which valve separates the right atrium from the right ventricle?

• a.Mitral valve
• b.Aortic valve
• c.Tricuspid valve✓
• d.Pulmonic valve

The tricuspid valve, named for its three cusps, lies between the right atrium and right ventricle and prevents backflow during ventricular systole. The mitral valve is the corresponding atrioventricular valve on the left side. The pulmonic and aortic valves are semilunar valves that guard the exits from the right and left ventricles.

When does blood flow into the coronary arteries to supply the heart muscle itself?

• a.During ventricular systole, when pressure is highest
• b.During ventricular diastole, when the heart muscle is relaxed✓
• c.Only during atrial contraction
• d.Continuously and equally throughout the cardiac cycle

The coronary arteries branch from the base of the aorta and fill primarily during diastole, because during systole the contracting myocardium compresses the vessels running through it. This is one reason very fast heart rates, which shorten diastole, can provoke ischemia. Atrial contraction contributes to ventricular filling, not coronary perfusion, and coronary flow is distinctly phasic rather than constant.

How is cardiac output calculated?

• a.Systolic pressure minus diastolic pressure
• b.Heart rate divided by stroke volume
• c.Stroke volume multiplied by blood pressure
• d.Heart rate multiplied by stroke volume✓

Cardiac output equals heart rate times stroke volume, the amount of blood ejected by the left ventricle each beat, and it is normally about 4 to 8 liters per minute in an adult. Subtracting diastolic from systolic pressure gives pulse pressure. Dividing rate by stroke volume or multiplying stroke volume by blood pressure produces no meaningful physiologic measurement.

What happens during ventricular diastole?

• a.The ventricles relax and fill with blood✓
• b.The ventricles contract and eject blood
• c.The atrioventricular valves snap shut
• d.Blood is forced into the aorta and pulmonary artery

Diastole is the relaxation and filling phase, during which the atrioventricular valves are open and blood flows from the atria into the ventricles. Contraction and ejection define systole. The atrioventricular valves close at the start of systole, and blood enters the great vessels only when the ventricles contract.

A patient arrives with crushing chest pain radiating to the left jaw. The 12-lead shows ST segment elevation in leads II, III, and aVF. What does this pattern most likely represent?

• a.Normal early repolarization
• b.Atrial enlargement
• c.Pericardial friction
• d.An acute myocardial infarction involving the inferior wall✓

ST segment elevation in a group of anatomically related leads is the classic sign of acute myocardial injury, and leads II, III, and aVF look at the inferior wall of the left ventricle. The technician does not diagnose but must recognize the pattern and notify the nurse or physician immediately. Atrial enlargement changes the P wave, not the ST segment, and benign early repolarization does not appear with this presentation of severe radiating pain.

How does stable angina differ from a myocardial infarction?

• a.Angina causes permanent muscle death; an infarction does not
• b.Angina is temporary ischemia relieved by rest or nitroglycerin, while an infarction is prolonged blockage causing tissue death✓
• c.Angina always shows ST elevation; an infarction never does
• d.Angina occurs only at rest; an infarction occurs only with exertion

Angina is chest pain from temporary oxygen shortage in the myocardium, typically brought on by exertion and relieved within minutes by rest or nitroglycerin, and it may show transient ST depression or T wave inversion. A myocardial infarction is sustained occlusion that kills muscle tissue and often produces ST elevation and later Q waves. It is the infarction, not angina, that causes permanent damage.

A patient scheduled for an EKG has ankle swelling, shortness of breath when lying flat, and a history of congestive heart failure. What is happening physiologically?

• a.The coronary arteries are completely blocked
• b.The SA node has stopped firing
• c.The heart cannot pump effectively, so blood backs up into the lungs and peripheral tissues✓
• d.The electrical conduction system has been severed

In congestive heart failure the weakened ventricle cannot move the volume delivered to it, so fluid backs up behind the failing side, causing pulmonary congestion and orthopnea on the left and peripheral edema on the right. Complete coronary occlusion describes an infarction. SA node failure produces an escape rhythm, and a severed conduction system is not a mechanism of chronic heart failure.

Long-standing untreated hypertension most commonly produces which EKG-related change?

• a.Left ventricular hypertrophy with increased QRS voltage in the left-sided leads✓
• b.Absent P waves in every lead
• c.A shortened QT interval below 0.20 second
• d.Pacemaker spikes before each QRS

Chronic high blood pressure forces the left ventricle to work against increased resistance, so the muscle thickens and generates larger voltage, appearing as tall R waves in the left-sided leads and deep S waves in V1 and V2. Absent P waves indicate atrial fibrillation or a junctional rhythm. A QT under 0.20 second is not a hypertension finding, and pacemaker spikes come from an implanted device.

Which layer of the heart wall is the thick muscular layer responsible for contraction?

• a.Pericardium
• b.Endocardium
• c.Epicardium
• d.Myocardium✓

The myocardium is the middle, muscular layer whose contraction generates the pumping force, and it is the tissue damaged in a myocardial infarction. The endocardium is the thin inner lining in contact with the blood. The epicardium is the outer surface layer of the heart, and the pericardium is the surrounding sac.

Why is the left ventricle the thickest chamber of the heart?

• a.It holds the largest volume of blood
• b.It must generate enough pressure to pump blood through the entire systemic circulation✓
• c.It contains the SA node and needs extra muscle to protect it
• d.It receives blood directly from the venae cavae

The left ventricle pumps against the high resistance of the systemic circuit, so its wall is roughly three times thicker than the right ventricle, which only pumps to the nearby low-pressure lungs. Both ventricles eject about the same volume per beat, so volume is not the reason. The SA node sits in the right atrium, and the venae cavae empty into the right atrium.