CET NHA Certified EKG Technician - Set 3 - Part 1

Correct Answer: The mediastinum behind the sternum

The heart sits in the mediastinum, the central compartment of the thoracic cavity between the lungs and behind the sternum. About two-thirds of the heart lies to the left of the body's midline. Option a is incorrect because the pleural cavity holds the lungs, with one cavity on each side of the mediastinum. The pleural cavities are pulmonary spaces and do not contain the heart at all. Option c is incorrect because the abdominal cavity sits below the diaphragm and holds the digestive and urinary organs. The heart lives above the diaphragm in the chest, not in the abdomen. Option d is incorrect because the peritoneum is the membrane lining the abdominal cavity around organs like the stomach and intestines. Peritoneum is an abdominal structure entirely unrelated to the thoracic location of the heart.

Correct Answer: The pericardium sac

The pericardium is the double-layered fibroserous sac that surrounds the heart, with a tough outer fibrous layer and an inner serous portion. Fluid between the serous layers lubricates the heart as it beats. Option a is incorrect because the endocardium is the smooth innermost lining of the heart chambers, continuous with the great vessels and valves. The endocardium is a single layer inside the heart, not the surrounding sac. Option b is incorrect because the myocardium is the thick middle muscular layer of the heart wall that does the contractile work. Muscle tissue is not a sac and does not surround the heart externally. Option c is incorrect because the epicardium is the visceral layer of the pericardium that adheres tightly to the heart surface. The epicardium is only part of the answer; the full sac includes the parietal layer and fibrous covering too.

Correct Answer: The myocardium as muscular middle layer

The myocardium is the thick muscular middle layer that performs the contractile work of the heart during systole. Its strength shapes the heart's pumping ability and is what shows on EKG as ventricular depolarization. Option b is incorrect because the endocardium is a thin endothelial lining that smooths blood flow inside the chambers and is continuous with valve surfaces. It does not generate force and contains no contractile fibers of its own. Option c is incorrect because the visceral pericardium, also called the epicardium, is the outer surface of the heart and part of the serous pericardium. Its role is protective rather than contractile and includes no muscle tissue. Option d is incorrect because the fibrous pericardium is the tough outer layer of the surrounding sac that anchors the heart to nearby structures. Anchoring tissue does not contract and is not part of the heart wall itself.

Correct Answer: Higher systemic afterload to overcome

The left ventricle is thicker because it must generate enough pressure to drive blood through the entire systemic circulation, which presents much higher afterload than the pulmonary circuit faces. Muscle thickness scales with the pressure work required. Option a is incorrect because both ventricles handle similar stroke volumes despite their different wall thicknesses. Volume alone does not drive the thickness asymmetry that pressure work creates between left and right. Option b is incorrect because conduction tissue is distributed throughout the heart along specialized pathways rather than concentrated in one ventricle. Electrical tissue density does not explain the muscular thickness difference between chambers. Option d is incorrect because heart weight is a whole-organ measure that does not explain the specific asymmetry between left and right ventricular walls. Overall mass and chamber-specific wall thickness are different anatomical concepts.

Correct Answer: The superior and inferior vena cava

The superior and inferior vena cava return deoxygenated systemic blood to the right atrium, joined by the coronary sinus which drains the heart muscle itself. Blood then passes through the tricuspid valve into the right ventricle. Option a is incorrect because the aorta is the major outflow vessel from the left ventricle, and the pulmonary trunk is the outflow vessel from the right ventricle. Both are leaving vessels rather than incoming drainage to the right atrium. Option b is incorrect because the pulmonary veins carry oxygenated blood from the lungs into the left atrium, not the right. Routing them to the right atrium would mix oxygenated blood with deoxygenated venous return. Option c is incorrect because coronary arteries supply oxygenated blood from the aorta to the heart muscle, flowing outward from the aorta. These vessels deliver, not drain, blood and have no role in systemic venous return.

Correct Answer: The mitral or bicuspid valve

The mitral valve, also called the bicuspid valve because it has two cusps, sits between the left atrium and the left ventricle. It opens during ventricular diastole and closes during ventricular systole to prevent backflow into the atrium. Option b is incorrect because the tricuspid valve, named for its three cusps, separates the right atrium and right ventricle on the opposite side of the heart. The tricuspid valve has no role on the left side of the circulation. Option c is incorrect because the aortic semilunar valve sits between the left ventricle and the aorta as the outflow valve, not between two left-sided chambers. Outflow valves and atrioventricular valves serve different roles in the cycle. Option d is incorrect because the pulmonary semilunar valve sits between the right ventricle and the pulmonary trunk on the right side of the heart. It is part of the pulmonary outflow pathway and is unrelated to left-sided drainage.

Correct Answer: Closure of the atrioventricular valves

The first heart sound S one is produced by the closure of the atrioventricular valves, the mitral and tricuspid, at the beginning of ventricular systole. Closure of these valves marks the transition from filling to contraction. Option a is incorrect because closure of the semilunar valves produces the second heart sound S two at the start of ventricular diastole. The semilunar valves mark the end of systole rather than the beginning, which is what S one signals. Option b is incorrect because opening of the atrioventricular valves is typically silent in a normal heart and does not generate an audible sound. Valve opening events do not produce the classic lub heard during auscultation. Option d is incorrect because opening of the semilunar valves also occurs silently in a normal heart and contributes no audible sound. Both valve-opening events are usually quiet, while closure produces the heart sounds that clinicians hear.

Correct Answer: About twenty to thirty percent at rest

The atrial kick contributes about twenty to thirty percent of ventricular filling at rest, with a larger share during exercise when filling time shortens. The remainder of filling occurs passively as ventricles relax during early and mid-diastole. Option a is incorrect because five percent dramatically underestimates the atrial contribution to ventricular filling. Such a low number would suggest atrial kick loss has little hemodynamic effect, which contradicts the clinical importance of atrial function. Option c is incorrect because fifty percent overstates the atrial contribution by roughly double. The bulk of ventricular filling actually occurs passively during early diastole before the atrial kick adds its final share. Option d is incorrect because seventy percent reverses the relative roles of passive filling and atrial contraction in the cardiac cycle. Passive filling, not atrial contraction, accounts for the majority of ventricular filling at rest.

Correct Answer: About zero point eight seconds

At a resting heart rate near seventy-five beats per minute, one full cardiac cycle takes about zero point eight seconds, with roughly zero point three seconds in systole and zero point five seconds in diastole. Option a is incorrect because three point two seconds would correspond to roughly nineteen beats per minute, far below any physiologic resting rate. The number is off by a factor that places it well outside normal cardiac physiology. Option b is incorrect because two seconds per cycle would correspond to roughly thirty beats per minute, a profound bradycardia inconsistent with a resting rate of seventy-five. The number is inconsistent with the stated heart rate. Option c is incorrect because one point five seconds per cycle would correspond to about forty beats per minute, slower than the resting rate described. Cycle length and heart rate are inverse, and this option mismatches them.

Correct Answer: Anchor the valve leaflets during contraction

The chordae tendineae anchor the atrioventricular valve leaflets to the papillary muscles, and during ventricular contraction the papillary muscles tense to prevent valve prolapse into the atria. Their combined work keeps blood moving forward. Option b is incorrect because the semilunar valves open and close based on pressure differences across the valve, not through any action of the chordae tendineae. Chordae are anatomically tied only to the atrioventricular valves. Option c is incorrect because atrial depolarization is triggered by the SA node and conducted through atrial tissue, not by any mechanical anchoring structure. Chordae tendineae have no electrical role in the conduction system at all. Option d is incorrect because coronary blood flow continues during systole at a reduced rate and is not blocked by any cardiac valve apparatus. Chordae tendineae have nothing to do with coronary perfusion at any phase of the cycle.

Correct Answer: Inferior wall and right coronary artery

Leads two, three, and aVF view the inferior wall of the heart, which is most commonly supplied by the right coronary artery in right-dominant circulations. ST elevation in this group strongly suggests inferior wall injury from RCA occlusion. Option a is incorrect because the anterior wall is viewed by precordial leads V one through V four and supplied by the left anterior descending artery. The inferior lead group does not look at the anterior wall at all. Option b is incorrect because the lateral wall is viewed by leads one, aVL, V five, and V six and is most often supplied by the left circumflex artery. Lateral findings come from a different lead group than the inferior triad. Option d is incorrect because the posterior wall is evaluated indirectly through reciprocal changes in V one through V three or with dedicated posterior leads. The inferior leads do not provide a posterior view of the heart at all.

Correct Answer: The left anterior descending artery

Leads V one through V four image the anterior wall of the left ventricle and the interventricular septum, which are supplied by the left anterior descending artery. Acute changes in this group most often reflect LAD occlusion. Option a is incorrect because the right coronary artery supplies the inferior wall, which shows changes in leads two, three, and aVF rather than V one through V four. Inferior and anterior territories are anatomically distinct from each other. Option b is incorrect because the left circumflex artery supplies the lateral wall, which shows changes in leads one, aVL, V five, and V six. Lateral and anterior lead groups view different parts of the heart with different coronary sources. Option c is incorrect because the right marginal branch supplies a small portion of the right ventricle and does not produce anterior wall lead changes. Right ventricular changes are best seen with right-sided leads, not the standard anterior precordials.

Correct Answer: The lateral wall of the left ventricle

Leads one, aVL, V five, and V six together view the lateral wall of the left ventricle. The combination of high lateral leads from the limb side and low lateral leads from the precordials covers the wall. Option b is incorrect because the septal wall is viewed primarily by leads V one and V two, which sit closest to the interventricular septum. The septal view does not extend to the high lateral or far lateral leads in this group. Option c is incorrect because the inferior wall is viewed by leads two, three, and aVF and corresponds to the diaphragmatic surface of the heart. Inferior leads are limb leads in a different orientation than the lateral group. Option d is incorrect because the right ventricular free wall is best evaluated with right-sided precordial leads, particularly V four R. Standard left-sided lateral leads do not provide a useful view of the right ventricle.

Correct Answer: Lead V four R on the right side

V four R, placed at the fifth intercostal space on the right midclavicular line as a mirror of V four, is the most useful additional lead for diagnosing right ventricular infarction. ST elevation here flags RV involvement. Option a is incorrect because V seven sits on the posterior axillary line on the back and is part of the posterior lead set. Posterior leads evaluate the posterior wall rather than the right ventricle. Option b is incorrect because aVR is a standard augmented limb lead that views the heart from the right shoulder. While always recorded, aVR does not provide the targeted right ventricular view that a right-sided precordial lead does. Option d is incorrect because V three is a standard left-sided precordial lead between V two and V four. It looks at the anterior wall, not the right ventricle, and is not the additional lead for RV evaluation.

Correct Answer: Posterior wall myocardial infarction

ST depression in V one through V three with tall R waves in those leads is a reciprocal mirror image of ST elevation and pathologic Q waves on the posterior wall. Posterior leads V seven through V nine confirm the suspicion. Option a is incorrect because anterior wall infarction presents with ST elevation, not depression, in V one through V four. Direct injury in those leads shows elevation rather than the depression described in the scenario. Option c is incorrect because lateral wall infarction shows changes in leads one, aVL, V five, and V six rather than the anteroseptal leads V one through V three. The lead group is different and the pattern would not match. Option d is incorrect because right ventricular infarction is best diagnosed with V four R, where ST elevation appears. RV infarction does not typically produce the tall R wave and ST depression pattern in V one through V three.

Correct Answer: Heart rate multiplied by stroke volume

Cardiac output equals heart rate multiplied by stroke volume, where stroke volume is the amount of blood ejected per beat. Changes in either factor scale the total flow the heart provides per minute. Option a is incorrect because preload and afterload describe loading conditions on the ventricle rather than direct multipliers of cardiac output. They influence stroke volume but are not the formula's two terms. Option b is incorrect because ejection fraction is the percentage of end-diastolic volume ejected per beat, which is a related but separate index. Cardiac output uses stroke volume in absolute units, not the percentage ejection fraction. Option c is incorrect because dividing stroke volume by preload does not produce a meaningful output measure in cardiac physiology. Cardiac output is a product of rate and stroke volume, not a quotient.

Correct Answer: Norepinephrine acting on beta one receptors

Sympathetic effects on the heart are mediated by norepinephrine acting on beta one adrenergic receptors, producing positive chronotropy, inotropy, and dromotropy. This neurotransmitter and receptor pair underlies the body's stress and exercise response on the heart. Option b is incorrect because acetylcholine acting on muscarinic receptors mediates parasympathetic effects via the vagus nerve, which slow the heart. The parasympathetic pair acts opposite to the sympathetic system described in the question. Option c is incorrect because dopamine has prominent effects on the kidney and other systems and is not the primary endogenous sympathetic neurotransmitter at the cardiac beta one receptor. Dopamine plays a different physiologic role from norepinephrine here. Option d is incorrect because serotonin is a neurotransmitter primarily involved in mood, gastrointestinal motility, and platelet function. Serotonin does not mediate the standard sympathetic effects on the sinoatrial node or

Correct Answer: Slows the sinoatrial node firing rate

Vagal stimulation slows the sinoatrial node firing rate and delays atrioventricular conduction, decreasing heart rate. Parasympathetic tone normally counterbalances the SA node's higher intrinsic rate to keep the resting heart rate in the normal range. Option a is incorrect because vagal stimulation slows AV node conduction rather than speeding it up. Sympathetic activity would speed conduction, while parasympathetic activity does the opposite at the AV node. Option b is incorrect because parasympathetic effects on ventricular contractility are minimal, and the major effect on contractility is sympathetic. Vagal effects are concentrated on the SA and AV nodes rather than on ventricular muscle force. Option d is incorrect because vagal activity decreases heart rate rather than increasing it. Increased resting heart rate is the sympathetic pattern, while increased vagal tone produces relative bradycardia.

Correct Answer: Resting parasympathetic tone slows the rate

At rest, parasympathetic vagal tone dominates and slows the SA node's intrinsic rate of about one hundred beats per minute down to the typical resting range. Removing vagal input lets the rate climb back toward that intrinsic value. Option a is incorrect because the AV node fires only as a backup at a slower intrinsic rate when the SA node fails. A backup pacemaker does not explain why the dominant SA node's rate appears slower than its intrinsic value. Option b is incorrect because the myocardium does not absorb electrical activity in a way that slows the firing rate of the SA node. Myocardial conduction and SA node firing rate are governed by different mechanisms entirely. Option c is incorrect because the lungs have no direct role in slowing the conduction system or the SA node's rate. Respiratory rhythm affects heart rate variability slightly through vagal modulation, which is a parasympathetic effect.

Correct Answer: Preload, afterload, and contractility

Preload, afterload, and contractility are the three main determinants of stroke volume. Preload reflects venous return, afterload reflects vascular resistance, and contractility reflects the inherent strength of myocardial fiber shortening during systole. Option b is incorrect because heart rate is a separate factor in the cardiac output equation rather than part of stroke volume itself. Blood pressure and oxygen are downstream consequences and inputs, not the three classic stroke volume factors. Option c is incorrect because mean arterial pressure and venous tone are related concepts but do not by themselves capture the three classic stroke volume factors. The standard framework names preload, afterload, and contractility specifically. Option d is incorrect because sympathetic tone is one influence among several but is not the sole determinant. Stroke volume responds to several factors that act independently and combine through cardiac physiology.