CRL Quiz 2 2009

1

Which one of the following statements regarding the action potential of a cell in the cardiac sinoatrial (SA) node is NOT CORRECT?


  An increase in the slope of the pacemaker potential would reduce the heart rate.

  An increase (more positive) in the threshold potential would reduce the heart rate.

  An increase (less negative) in the starting voltage of the pacemaker potential would increase the heart rate.

  Increased permeability to sodium is important in generating the upstroke of the SA node cell action potential.

  Increased permeability to potassium is important in repolarisation.


An increase in the slope of the pacemaker potential would hasten the rate at which the membrane potential approaches the threshold potential. Therefore, the pacemaker would fire more frequently and heart rate would increase, not decrease as stated in A.

2

Which one of the following statements regarding cardiac myocyte contraction is NOT CORRECT?


  The binding of calcium to troponin is important in the process of contraction.

  Myocyte excitation causes extracellular calcium to move into the cytosol.

  Extracellular calcium is the major source accounting for the increase in cytosolic calcium that triggers contraction.

  Hormones such as adrenaline will increase intracellular calcium.

  When tropomyosin shifts it exposes a key binding site on G-actin.


It is the calcium from the intracellular stores in the sarcoplasmic reticulum that provides the majority of calcium for the contraction. Although the release of the SR calcium is triggered by the influx of calcium from the extracellular environment, the total amount of calcium entering the cytosol is less than that released by the SR. Hence option C is untrue.

3

A 60-year-old man presents to the Emergency Department with severe shortness of breath. An echocardiogram shows that his left ventricle is dilated and has severely decreased function. What intracardiac pressure is most likely to be elevated?


  Left ventricular end-diastolic pressure.

  Pulmonary artery systolic pressure.

  Right atrial pressure.

  Right ventricular systolic pressure.

  Left ventricular systolic pressure.


Most likely to be elevated. He has left heart failure – LVEDP goes up due to fluid retention – remember Starling Curves.
B is incorrect: May be up a little.
C is incorrect: May be up a little.
D is incorrect: May be up a little.
E is incorrect: May be down.

4

Which one of the following statements can increase by more than 2 times during exercise?


  Arterial blood pressure.

  Heart Rate.

  Peripheral resistance.

  Contractility.

  End-diastolic volume.


A is incorrect: Will increase but not by more than 2 times.
C is incorrect: Goes down.
D is incorrect: Will increase but not by more than 2 times.
E is incorrect: Doesn’t go up or down much.

5

A 70-year-old woman has severe peripheral oedema. This is most likely to be associated with


  low jugular venous pressure (JVP).

  high plasma protein concentration.

  blockage of lymphatics.

  overuse of diuretics.

  arterial hypertension.


A is incorrect: JVP high if anything.
B is incorrect: A low plasma protein concentration would give oedema.
D is incorrect: Underuse of diuretics in someone with heart failure would cause oedema.
E is incorrect: Irrelevant to oedema.

6

Myocardial infarction differs from unstable angina in that infarction


  causes more chest pain.

  is more common.

  is due to coronary artery spasm.

  occurs more often at night.

  is more likely to result in death.


A is incorrect: Both cause chest pain.
B is incorrect: Both are common.
C is incorrect: Neither is usually due to spasm.
D is incorrect: Both can occur 24/7.

7

Which one of the following is considered the primary mechanism of action of the cardiac glycosides used in the management of heart failure?


  Reduction of intracellular Na+ concentration.

  Inhibition of Na+ and K+ exchange.

  Elevation of intracellular ATP concentration.

  Stimulation of cAMP production.

  Elevation in Ca2+ release from the sarcoplasmic reticulum.


While there is evidence that some cardiac glycosides can directly elevate Ca2+ release from the sarcoplasmic reticulum. Na+/K+ ATPase is regarded the primary target accessible to the cardiac glycosides. Inhibition results in accumulation of intracellular Na+ which is then exchanged for Ca2+ leading to an increase in intracellular Ca2+.

8

Which one of the following statements about the use of lignocaine as an antiarrhythmic agent is NOT CORRECT?


  It is given by intravenous administration.

  It may cause drowsiness.

  It may cause convulsions.

  It may increase action potential duration.

  It may cause bradycardia.


Lignocaine is representative of the class 1b anti-arrhythmics that reduce action potential duration. It is given intravenously for use as an antiarrhthmic but because it inhibits activation of the Na+ channel it is also useful as a local anaesthetic. Drowsiness & convulsions following intravenous administration relate to inhibition of neuronal activity.

9

Which one of the following class of antihypertensive agents will most likely result in postural hypotension?


  β-Adrenoceptor antagonists.

  Ca2+-channel inhibitors.

  Thiazide diuretics.

  Angiotensin receptor antagonists.

  α-Adrenoceptor antagonists.


All antihypertensive drugs have the potential to cause postural hypotension. The α-drenoceptor antagonists block sympathetically mediated vasoconstriction and will directly impair normal homeostatic reflexes.

10

Which one of the following statements about the use of the nitrovasodilator glyceryltrinitrate in the management of stable angina is correct?


  It will decrease venous capacitance and decrease preload.

  It will increase myocardial work.

  It will reduce endocardial blood flow.

  It can only be used to treat acute attacks because tolerance develops to its actions.

  It will have a greater effect on large arteries and veins compared to arterioles.


Much of the benefit of the nitrates in stable angina is by reducing preload through venodilation rather than an effect on coronary vessels that are probably already maximally dilated to meet the O2 demand of the heart. Endocardial blood flow is increased by reducing pressures on the ventricular wall. Patches can be used for long-term treatment as long as there are periods where the drug is not administered, usually overnight.

11

Which one of the following statements regarding haemostasis is NOT CORRECT?


  Haemostasis is the arrest of bleeding from injured vessels.

  Haemostasis involves the processes of vascular constriction at the site of the lesion.

  Haemostasis involves the processes of platelet production.

  Haemostasis involves the processes of platelet adhesion.

  Haemostasis involves the processes of blood coagulation.

12

A 45-year-old male has been receiving warfarin therapy, following surgery six months ago to replace his mitral valve with a metallic prosthetic valve. Until recently his INR has been stable and within the desired range. He presents for assessment of his clotting time following an episode of acute alcohol intoxication. Following this episode of acute alcohol intoxication, one might expect that clotting time in this patient might be


  increased, as a consequence of induction of cytochrome p450 pathways.

  increased, as a consequence of reduced clearance of warfarin.

  decreased, as a result of reduced plasma protein binding.

  decreased, because of enhanced platelet aggregation.

  unchanged, because warfarin does not affect preformed clotting factors.


Clotting time is the time taken for a sample of the patient's blood to clot. Hence an increase in clotting time suggests an increase in the activity of warfarin, and a decrease in clotting time suggests a decrease in warfarin activity.

Acute ingestion of alcohol is likely to decrease warfarin clearance, as alcohol and warfarin compete for clearance via cytochrome p450 pathways. Hence answer B is correct. Alcohol competes with warfarin for clearance via cytochrome p450 pathways, leading to higher blood warfarin levels and increased clotting time.

A is incorrect: As induction of cytochrome p450 pathways (a consequence of chronic alcohol consumption), would result in increased warfarin clearance, lower blood warfarin levels, and hence decreased clotting times.

C is incorrect: Reduced plasma protein binding would increase free warfarin, hence leading to increased warfarin activity and increased clotting time.

D is incorrect: Warfarin affects the formation of clotting factors- it has no effect on platelet aggregation.

E is incorrect: This is not the best answer- whilst it is true that warfarin does not affect preformed clotting factors, acute alcohol intoxication will cause an immediate decrease in warfarin clearance, hence causing an almost immediate increase in warfarin levels.

The question does not make clear the time interval since the bout of intoxication, but as there is no reference to the patient being intoxicated on presentation, and as there is constant turnover of clotting factors, it would be reasonable to assume that a short period of time has elapsed since the alcohol consumption. It can therefore reasonably be assumed that the increase in warfarin levels will have resulted in reduced formation of clotting factors and increased clotting time. (see slide 30 Increased Warfarin Activity)

13

Longstanding, mild or moderate systemic hypertension is associated with which one of the following?


  Hypertrophy of left ventricular myocardium.

  Fibrinoid necrosis of arteriolar walls.

  Progression to encephalopathy and renal failure in weeks or months.

  Proliferative arteriopathy with rapid occlusion of arterial lumens in kidney and other organs.


The other changes are all seen in very high levels of hypertension (so called malignant or accelerated hypertension) but are not seen in milder degrees of hypertension.

14

Which one of the following statements concerning atheroma is correct?


  It can be responsible for reducing venous drainage from the liver and other organs.

  It predisposes to bacterial infection within the arterial lesions.

  It is only seen in patients with hyperlipidaemia.

  The plaques may rupture, triggering thrombosis.


The process does not involve veins, it does not seem to predispose to bacterial infection in the lesions, and it may be seen in the absence of hyperlipidaemia.

15

A 68-year-old man with a long history of ischaemic heart disease dies suddenly at home. At autopsy you find an area of tough, pale and almost white tissue replacing an area of his left ventricular myocardium. Which one of the following statements is correct?


  This is most in keeping with myocardial infarction occurring minutes before he died.

  This is most in keeping with myocardial infarction occurring about 24 hours before he died.

  This is most in keeping with an old infarct (i.e. occurring at least many months before he died).

  This is likely unrelated to his ischaemic heart disease.


This describes a mature fibrous scar replacing part of the muscle in his heart and is the appearance of an old infarct, at least months before his death and possibly many years.