TBL11 - Heart

Question 1

What is the pericardiac sac attached to? Where is the heart situated? What partially covers the anterior surface of the heart?

Answer 1

1) The pericardial sac is attached to the central tendon of the diaphragm
2) The heart is situated obliquely two-thirds to the left of the midsternal line
3) The sternum and costal cartilages partially cover the anterior surface of the heart

Question 2

How are isolated dextrocardia and dextrocardia associated with situs inversus distinguished?

Answer 2

1) Abnormal folding of the embryonic heart may cause the position of the heart to be completely reversed so that the apex is misplaced to the right instead of the left—dextrocardia
2) Dextrocardia is associated with mirror image positioning of the great vessels and arch of the aorta. This anomaly may be part of a general transposition of the thoracic and abdominal viscera (situs inversus), or the transposition may affect only the heart (isolated dextrocardia)
3) In dextrocardia with situs inversus, the incidence of accompanying cardiac defects is low, and the heart usually functions normally. In isolated dextrocardia, however, the congenital anomaly is complicated by severe cardiac anomalies, such as transposition of the great arteries

Question 3

What portion of the anterior surface of the heart do the right and left ventricles occupy? Where does the apex reside?

Answer 3

1) The right ventricle forms two thirds of the anterior surface of the heart and the left ventricle occupies the other third, which includes the apex of the heart
2) The apex resides at the auscultation site for the mitral valve

Question 4

What occupies the posterior aspect of the heart? What is it formed by? What do the left and right ventricles form?

Answer 4

1) The base of the heart, which occupies the posterior aspect of the heart, is formed mainly by the left atrium with a small contribution by the right atrium
2) The left ventricle forms two thirds of the diaphragmatic (inferior) surface of the heart and the right ventricle occupies the other third of the inferior surface

Question 5

What forms the right border of the heart? The inferior border? The left border? The superior border? What emerges from the superior border from the anterior view of the heart?

Answer 5

1) The right border of the heart is formed by the right atrium extending between the SVC and IVC
2) The right and left ventricles form the inferior and left borders, respectively
3) Both atria form the superior border of the heart
4) In the anterior view, the pulmonary trunk, aorta, and SVC emerge from the superior border

Question 6

What do the right and left auricles overlap? What is the function of the auricles?

Answer 6

1) The right auricle overlaps the ascending aorta and the left auricle overlaps pulmonary trunk
2) The auricles, which are pouch-like projections from the atria, increase atrial capacity

Question 7

How is the right border of the heart depicted in a radiograph? What does the left border of this structure consist of? What creates small and large aortic knobs in this structure?

Answer 7

1) A silhouette is the image of a person, animal, object or scene represented as a solid shape of a single colour, usually black, its edges matching the outline of the subject
2) The heart is depicted as a radiographic cardiovascular silhouette
3) The left border of the silhouette is formed by the arch of the aorta, pulmonary trunk, left auricle, and left ventricle
4) The right border of the silhouette is formed by the right brachiocephalic vein, SVC, right atrium, and IVC
5) Decreased blood flow into the aorta creates small “aortic knobs” and increased flow into the aorta creates large “aortic knobs” in the silhouette

Question 8

Compare the posterior and anterior aspects of the interior wall of the right atrium. Notice the oval fossa in the interatrial septum. What does the coronary sinus empty into?

Answer 8

1) The posterior aspect of the interior wall of the right atrium is smooth and the anterior aspect is ridged by cardiac muscle
2) The coronary sinus, the main vein of the heart, empties into the right atrium along with the IVC and SVC

Question 9

Describe the outflow and inflow portions of the interior wall of the right ventricle. What is the function of the chordae tendineae?

Answer 9

1) The outflow portion of the interior wall of the right ventricle is smooth
2) The inflow portion is ridged by cardiac muscle
3) The fibrous chordae tendineae connect free ends of the three cusps of the tricuspid valve to papillary muscles that project into the ventricular lumen

Question 10

How do the chordae tendineae act during systole? How does this allow blood to flow through the open pulmonary valve?

Answer 10

1) The chordae tendineae act as cords attaching to a parachute. During systole, papillary muscle contraction tenses the cords to insure tight closure of the cusps thereby preventing retrograde flow into the right atrium
2) There is unidirectional blood flow from the right ventricle through the open pulmonary valve

Question 11

What does pulmonary hypertension result in? What does prolonged pulmonary hypertension result in?

Answer 11

1) Pulmonary hypertension (high blood pressure in the pulmonary arteries typically in response to an increased resistance to blood flow) requires the right ventricle to pump more forcefully
2) Prolonged hypertension creates right ventricular hypertrophy that can lead to cor pulmonale i.e., progressive strain on the right ventricle that can lead to its failure

Question 12

Why are shortness of breath and cyanosis during physical activity often the first symptoms of cor pulmonale?

Answer 12

1) Cor pulmonale = failure of right ventricle
2) Cyanosis = not enough oxygenated blood
3) Shortness of breath = try to compensate by breathing quicker and then have a shortness of breath

Question 13

Describe the interior wall of the left atrium. What accounts for the left ventricular wall being nearly double in thickness of the right ventricular wall?

Answer 13

1) The interior wall of the left atrium is uniformly smooth and contains orifices for the four pulmonary veins
2) The marked difference in systemic and pulmonary arterial pressures accounts for left ventricular wall thickness nearly doubling that of the right ventricle

Question 14

Where does the esophagus run in relation to the four pulmonary veins connected to the heart?

Answer 14

The position of esophagus, which is immediately posterior to the left atrium, is also posterior to the medially anterior pericardial sac, where the four pulmonary veins that pierce the pericardial sac run

Question 15

What occupies the interior wall of the left ventricle except the smooth outflow portion?

Answer 15

Ridged cardiac muscle occupies the interior wall of the left ventricle except the smooth outflow portion

Question 16

During ventricular contraction, what does the ridged cardiac muscle prevent?

Answer 16

During ventricular contraction, the ridged cardiac muscle prevents suction that would occur with a flat surface and impair pumping efficiency

Question 17

What do the three cusps of the aortic valve lack? What does this result in?

Answer 17

Like the pulmonary valve, the three cusps of the aortic valve lack chordae tendineae attachments; thus, the valves are forced open during systole and thrust back into the closed position during diastole

Question 18

How are the mitral valve cusps positioned during diastole? How are these cusps positioned during systole? How does blood flow from the left ventricle?

Answer 18

1) During diastole, cusps of the mitral valve are open to enable refilling of the left ventricle with oxygenated blood
2) During systole, contraction of the anterior and posterior papillary muscles tightly closes the cusps to prevent retrograde flow into the left atrium
3) Unidirectional outflow from the left ventricle occurs through the open aortic valve during systole

Question 19

What are two classes of developmental abnormalities of the heart? What do septal defects of the heart cause after birth?

Answer 19

1) Developmental abnormalities of the heart include atrial septal defects (ASD) and ventricular septal defects (VSD)
2) After birth, the septal defects cause blood to shunt, based on pressure differentials, from the left side of the heart to the right side

Question 20

Describe an ASD murmur. Describe a VSD murmur.

Answer 20

1) With ASD, a systolic murmur is typically heard at the auscultation site for the pulmonary valve, which results from elevated forward flow through the open valve rather than from damage to the valvular cusps
2) VSD creates a systolic murmur along the left parasternal line over the 3rd and 4th ICS as a result of flow from the left ventricle through the defect into the right ventricle

Question 21

Why does ASD induce hypertrophy of the right atrium and ventricle, and dilation of the pulmonary trunk? Which form of atrial septal defect usually lacks clinical significance?

Answer 21

1) Large ASDs allow oxygenated blood from the lungs to be shunted from the left atrium through the ASD into the right atrium, causing enlargement of the right atrium and ventricle and dilation of the pulmonary trunk. This left to right shunt of blood overloads the pulmonary vascular system, resulting in hypertrophy of the right atrium and ventricle and pulmonary arteries
2) A probe-size patency (opening) is present in the superior part of the oval fossa in 15–25% of adults. These small openings, by themselves, cause no hemodynamic abnormalities and are, therefore, of no clinical significance and should not be considered forms of ASDs

Question 22

How can the left-to-right shunt associated with VSD cause pulmonary hypertension and subsequent heart failure?

Answer 22

A VSD causes a left to right shunt of blood through the defect. A large shunt increases pulmonary blood flow, which causes severe pulmonary disease (hypertension, or increased blood pressure) and may cause cardiac failure

Question 23

Where is the SA node positioned? The AV node? the AV bundle? The right and left bundle branches?

Answer 23

1) SA node is positioned in the right atrial wall adjacent to the SVC orifice
2) AV node is positioned in the interatrial septum adjacent to the coronary sinus orifice
3) AV bundle is positioned in the membranous portion of the interventricular septum
4) Right and left bundle branches are positioned in the endocardium of the ventricles

Question 24

What does the conducting system of the SA node and AV node allow for? What does the right coronary artery (RCA) supply? What does the left coronary artery (LCA) supply?

Answer 24

1) The conducting system enables coordinated contractions of the heart chambers during the cardiac cycle.
2) Typically, the RCA supplies:
a) The right atrium
b) Most of right ventricle
c) Part of the left ventricle (the diaphragmatic surface)
d) Part of the IV septum, usually the posterior third
e) The SA node (in approximately 60% of people)
f) The AV node (in approximately 80% of people)
3) Typically, the LCA supplies:
a) The left atrium
b) Most of the left ventricle
c) Part of the right ventricle
d) Most of the IVS (usually its anterior two thirds), including the AV bundle of the conducting system of the heart, through its perforating IV septal branches
e) The SA node (in approximately 40% of people)

Question 25

How does the moderator band contribute to the efficiency of right ventricular contraction?

Answer 25

1) The moderator band is a curved muscular bundle that traverses the right ventricular chamber from the inferior part of the IVS to the base of the anterior papillary muscle
2) This band is important because it carries part of the right branch of the AV bundle, a part of the conducting system of the heart to the anterior papillary muscle
3) This “shortcut” across the chamber seems to facilitate conduction time, allowing coordinated contraction of the anterior papillary muscle

Question 26

What two nerves form the cardiac plexus?

Answer 26

Together, the cardiopulmonary splanchnic and vagus nerves form the cardiac plexus

Question 27

What part of the cardiac plexus synapses with the cardiac muscle fibers that constitute the SA node? Compare the sympathetic and para-sympathetic affects on its pacemaker function. How do sympathetic fibers alter the force of ventricular contraction and blood flow in the coronary circulation?

Answer 27

1) Postsynaptic fibers of the plexus synapse with the cardiac muscle fibers that constitute the SA node
2) Adrenergic stimulation of the SA node and conducting tissue increases the rate of depolarization of the pacemaker cells while increasing atrioventricular conduction
3) Postsynaptic parasympathetic fibers release acetylcholine, which binds with muscarinic receptors to slow the rates of depolarization of the pacemaker cells and atrioventricular conduction and decrease atrial contractility
4) Sympathetic stimulation causes increased heart rate, impulse conduction, force of contraction, and, at the same time, increased blood flow through the coronary vessels to support the increased activity
5) Parasympathetic stimulation slows the heart rate, reduces the force of the contraction, and constricts the coronary arteries, saving energy between periods of increased demand

Question 28

How do the consequences differ after a heart block or bundle branch block? Which block could result after surgical correction of VSD?

Answer 28

1) In the case of a heart block (if the patient survives the initial stages), the ventricles will begin to contract independently at their own rate: 25–30 times per minute (much slower than the slowest normal rate (40–45 times per minute). The atria continue to contract at the normal rate if the SA node has been spared, but the impulse generated by the SA node no longer reaches the ventricles
2) Damage to one of the bundle branches results in a bundle branch block, in which excitation passes along the unaffected branch and causes a normally timed systole of that ventricle only. The impulse then spreads to the other ventricle via myogenic (muscle propagated) conduction, producing a late asynchronous contraction. In these cases, a cardiac pacemaker (artificial heart regulator) may be implanted to increase the ventricular rate of contraction to 70–80 per minute
3) With a VSD, the AV bundle usually lies in the margin of
the VSD. Obviously, this vital part of the conducting system must be preserved during surgical repair of the defect. Destruction of the AV bundle would cut the only physiological link between the atrial and ventricular musculature, also producing a heart block as described above

Question 29

What do some peripheral projecting fibers from the DRG at T1-T5 that course in anterior rami of respective spinal nerves do? Where do these fibers end up in segmental paravertebral ganglia?

Answer 29

1) Some peripheral projecting fibers from the DRG at T1-T5 that course in anterior rami of the respective spinal nerves enter the white communicating rami
2) In the segmental paravertebral ganglia, these sensory fibers join the postsynaptic sympathetic fibers that exit the ganglia and constitute the cardiopulmonary splanchnic nerves

Question 30

What do afferent fibers of the heart do? What types of fibers are they?

Answer 30

The afferent fibers convey pain from the heart to the CNS; thus, the fibers are designated as visceral sensory fibers

Question 31

What is unique about the distribution of the lateral cutaneous branch of spinal nerve T2? How is pain from a myocardial infarction typically felt as?

Answer 31

1) In addition to innervating the 2nd intercostal space, the lateral cutaneous branch also innervates the medial side of the left arm
2) Pain from myocardial infarction is typically felt as a crushing sensation beneath the sternum with pain extending onto the medial side of the left arm (recall the heart is situated obliquely two-thirds to the left of the midsternal line)

Question 32

How are anginal pain and pain from myocardial infarction distinguished?

Answer 32

1) Pain that originates in the heart is called angina or angina pectoris (L. angina, strangling pain + L. pectoris, of the chest). Individuals with angina commonly describe the transient (15 sec to 15 min) but moderately severe constricting pain as tightness in the thorax, deep to the sternum
2) The pain resulting from MI is usually more severe than with angina pectoris, and the pain resulting from the infarction does not disappear after 1–2 min of rest

Question 33

What branches does the LCA generate? What chambers of the heart does the LCA supply?

Answer 33

1) The LCA generates the circumflex artery and anterior interventricular artery (aka left anterior descending artery or LAD)
2) The LCA and its branches are the primary blood supply to the left atrium, most of the left ventricle, and the anterior two-thirds of the interventricular septum

Question 34

What branches does the RCA generate? What chambers of the heart does the RCA supply?

Answer 34

1) The RCA generates the marginal artery and posterior interventricular artery
2) The RCA and its branches are the primary blood supply to the right atrium, most of the right ventricle, and the posterior third of the interventricular septum

Question 35

Cite the three coronary arteries that account for nearly all cases of coronary artery occlusion. Describe the deficit caused by coronary artery occlusion.

Answer 35

1) The three most common sites of coronary artery occlusion and the percentage of occlusions involving each artery are the:
a) Anterior IV (LAD) branch of the LCA (40–50%)
b) RCA (30–40%)
c) Circumflex branch of the LCA (15–20%)
2) As coronary atherosclerosis progresses, the collateral channels connecting one coronary artery with the other expand, which may initially permit adequate perfusion of the heart during relative inactivity. Despite this compensatory mechanism, the myocardium may not receive enough oxygen when the heart needs to perform increased amounts of work. Strenuous exercise, for example, increases the heart’s activity and its need for oxygen. Insufficiency of blood supply to the heart (myocardial ischemia) may result in MI

Question 36

What accompanies the LAD? Where do the coronary veins empty and where do they terminate?

Answer 36

1) The great cardiac vein accompanies the LAD

2) The coronary veins empty into the coronary sinus and terminate in the right atrium

Question 37

Why are the coronary arteries perfused during diastole rather than systole?

Answer 37

During systole, the left ventricle pumps blood through the aorta, opening the aortic valves. These valves block the coronary arteries from having blood perfusion (flow). Therefore, during diastole when the valves close, blood can flow through the coronary arteries

Question 38

Why is coronary artery surgery in females often more difficult and less successful than in males?

Answer 38

Compared with men, women usually have coronary arteries with smaller diameters, so coronary artery surgery is often more difficult and may contribute to a poorer outcome