Cardiovascular

Question 1

Question

Answer 1

F. throbbing headaches

Question 2

Question

Answer 2

B. increased stiffness of the LV wall

Question 3

Features of S3

Answer 3

Heard just after S2

Caused by reverberant sound as blood fills an enlarged LV cavity during passive diastolic filling

Question 4

S3 associated pathology

Answer 4

Heart failure with reduced EF

High-output states (eg, thyrotoxicosis)

Mitral or aortic regurgitation

Question 5

Features of S4

Answer 5

Heard just before S1

Caused by blood striking a stiff LV wall during atrial contraction

Question 6

S4 associated pathologies

Answer 6

Concentric LV hypertrophy

Restrictive cardiomyopathy

Acute myocardial infarction

Question 7

Question

Answer 7

E. membrane K+ channels

This patient’s sudden-onset syncopal episode suggests a sudden cardiac arrhythmia. QT prolongation in an otherwise healthy young individual is usually congenital. The mutation most likely to cause QT-interval prolongation can be determined based on an understanding of cardiac electrophysiology. On an ECG tracing, the QT interval begins at the start of the QRS complex and ends at the end of the T wave. Therefore, the QT-interval reflects the cardiac myocyte action potential duration, which is determined in part by potassium (K+) currents through channel proteins. The mutations listed in the other answer choices would be less likely to directly affect the cardiac cell action potential duration.

There are two important congenital syndromes that cause QT prolongation:

Jervell and Lange-Nielsen syndrome (autosomal recessive, with neurosensory deafness)

Romano-Ward syndrome (more common, autosomal dominant, no deafness)

Both may predispose to torsades de pointes (a ventricular tachyarrhythmia) at a young age, causing syncopal episodes and possible sudden cardiac death.

(Choices A and C) Mutations affecting cardiac cell cytoskeletal proteins or the mitochondrial enzymes of oxidative phosphorylation are thought to cause the genetic form of dilated cardiomyopathy (DCM). DCM usually presents with gradual onset of left-sided heart failure (with symptoms like dyspnea on exertion initially), as opposed to the sudden syncopal episode in a previously asymptomatic patient described above.

(Choice B) Mutations in cardiac cell sarcomere proteins (e.g. beta-myosin heavy chain) underlie hypertrophic cardiomyopathy (HCM). Although HCM may present as syncope in a previously asymptomatic young person, the syncope of HCM is typically provoked by exertion. Additionally, QT prolongation is not generally found in HCM.

(Choice D) Mutations of a calcium-binding sarcoplasmic reticulum protein might underlie some cases of arrhythmogenic right ventricular cardiomyopathy (ARVC), aprogressive fibrofatty replacement of the right ventricular myocardium of uncertain pathogenesis. QT prolongation is not generally seen with ARVC.

Educational objective:
Unprovoked syncope in a previously asymptomatic young person may result from a congenital QT prolongation syndrome. The two most important congenital syndromes with QT prolongation, Romano-Ward syndrome and Jervell and Lange-Nielsen syndrome, are thought to result from mutations in a K+ channel protein that contributes to the delayed rectifier current (IK) of the cardiac action potential.

Question 8

Congenital syndromes that cause QT prolongation

Answer 8

• Jervell and Lange-Nielsen syndrome (autosomal recessive, with neurosensory deafness)
• Romano-Ward syndrome (more common, autosomal dominant, no deafness)

Question 9

Mutations of cardiac cytoskeleton or mitochondrial enzymes

Answer 9

Mutations affecting cardiac cell cytoskeletal proteins or the mitochondrial enzymes of oxidative phosphorylation are thought to cause the genetic form of dilated cardiomyopathy (DCM). DCM usually presents with gradual onset of left-sided heart failure (with symptoms like dyspnea on exertion initially), as opposed to the sudden syncopal episode in a previously asymptomatic patient described above.

Question 10

Mutations in cardiac cell sarcomere proteins

Answer 10

Mutations in cardiac cell sarcomere proteins (e.g. beta-myosin heavy chain) underlie hypertrophic cardiomyopathy (HCM). Although HCM may present as syncope in a previously asymptomatic young person, the syncope of HCM is typically provoked by exertion. Additionally, QT prolongation is not generally found in HCM.

Question 11

The most common cardiac abnormalities in Marfans Syndrome

Answer 11

The 2 most common cardiac abnormalities seen in MFS patients are mitral valve prolapse and cystic medial degeneration of the aorta.

In more than 75% of MFS patients, cystic medial degeneration of the aorta results in aneurysmal dilation. If untreated, this can cause aortic dissection, the most common cause of death in MFS patients.

The second most common cause of death is cardiac failure secondary to mitral valve prolapse and/or aortic regurgitation. For these reasons, MFS patients should be followed regularly by a cardiologist.

Question 12

Homocystinuria Pathophysiology

Answer 12

Autosomal recessive mutation causing cystathionine synthase deficiency

Question 13

Question

Answer 13

F. Venous blood mean CO2 content

Long-distance running and other forms of physical exercise cause increased oxidative metabolism of glucose and fatty acids in the skeletal muscle. This markedly increases the rates of O2 consumption and CO2 production, which must be balanced by increases in skeletal muscle perfusion and alveolar ventilation.

The cardiovascular response to exercise involves vasoconstriction in the splanchnic circulation and vasodilation in skeletal muscle, shunting blood toward exercising muscle. The vasodilation is predominant, resulting in overall decreased systemic vascular resistance. There is also an increase in heart rate and stroke volume that markedly increases cardiac output and O2 delivery to the tissues. Increased O2 extraction by the tissues leads to a concomitant increase in CO2 production, which is absorbed by the systemic capillaries and transported in high quantities via venous blood to the lungs, where it is expired.

(Choices A and B) Mean values for arterial O2 and CO2 content remain essentially constant during exercise, even during periods of intense exertion. This is likely accomplished via tight regulation of increases in alveolar ventilation and gas exchange efficiency.

(Choices C and D) Tissue pH typically decreases during exercise due to production of carbonic and lactic acid in active skeletal muscle. The acidic pH causes a decrease in hemoglobin affinity for O2 (ie, right shift in the O2-hemoglobin dissociation curve) to facilitate unloading of O2 in the tissues. Although venous pH may decrease significantly during moderate exercise, there is typically little change in arterial pH due to respiratory compensation.

(Choice E) Physiologic dead space (ie, the air in the respiratory system that does not participate in gas exchange) is decreased during exercise due to a decrease in pulmonary vascular resistance that allows perfusion of additional pulmonary capillary beds.

(Choice G) The mean O2 content of venous blood remains the same or decreases with exercise because the rate of O2 extraction by the tissues outpaces the rate of oxygen delivery (cardiac output). In most healthy individuals, cardiac output is the major limiting factor to O2 consumption during exercise.

Educational objective:
During physical exercise, there is increased skeletal muscle CO2 production that increases the CO2 content of venous blood. Arterial O2 and CO2 content remains constant via increases in alveolar ventilation and gas exchange efficiency. Venous O2 content remains constant or is decreased due to increased O2 extraction by the tissues that matches or exceeds the rate of oxygen delivery (ie, O2 consumption during exercise is limited by cardiac output).

Question 14

Varicocele pathophys

Answer 14

The right renal vein is a relatively short structure and runs anterior to the right renal artery before joining the inferior vena cava (IVC). The right gonadal vein also drains directly to the IVC. In contrast, the left renal vein is significantly longer and runs posterior to the splenic vein before crossing the aorta beneath the superior mesenteric artery. The left gonadal vein joins the left renal vein upstream of where it crosses the aorta and does not enter the IVC directly.

The pressure within the left renal vein is often higher than on the right due to compression between the aorta and the superior mesenteric artery (“nutcracker effect”). Pressure in the left renal vein can also be elevated due to compression from a left-sided abdominal or retroperitoneal mass. Persistently elevated pressure in the left renal vein can cause flank or abdominal pain, along with gross or microscopic hematuria (left renal vein entrapment syndrome). Increased pressure in the left gonadal vein results in valve leaflet failure and varices of the testicular pampiniform plexus (varicocele).