Schedule

PBL #	Overview Date	Discussion Date
1	28-Aug	4-Sept
2	4-Sept	11-Sept
3	11-Sept	25-Sept
4	25-Sept	2-Oct
5	2-Oct	9-Oct
6	9-Oct	23-Oct
7	23-Oct	30-Oct

Background:

Antiarrhythmic agents are a group of pharmaceuticals that are used to suppress abnormal rhythms of the heart, such as atrial fibrillation or ventricular tachycardia. Hundreds of drugs are classified as antiarrhythmic agents.

Antiarrhythmic agents are typically divided into five main classes, according to the primary mechanism of their anti-arrhythmic effect (Singh Vaughan Williams classification).

Problem:

Discuss in detail the mechanism of action of the five main classes of antiarrhythmic agents, and which types of arrhythmias each group of drugs is used to treat. In particular, you should describe how the mechanism of action of each drug class makes it particularly useful for treating particular arrhythmias. Your answer should additionally indicate the harmful side-effects of each class of drug.

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Background:

Congestive heart failure usually results in death within two years of diagnosis, but can be managed with a variety of drugs. The treatment varies depending on whether output of the left heart lags the right heart, or the right heart lags the left.

Problem:

Explain the common disease processes that result in left and right heart failure, and the medical treatments that are used to treat heart failure. You should be able to explain the physiological action of each therapy described, and how that action serves to alleviate the disease.

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Case 1

A patient with pericarditis develops cardiac tamponade. What are the effects of tamponade on the following parameters?

1. Right atrial pressure
2. Left atrial pressure
3. Left ventricular end systolic pressure
4. Mean arterial blood pressure
5. Systemic vascular resistance
6. Cardiac index

Draw left ventricular pressure-volume curves illustrating how the curves change from normal in a patient with cardiac tamponade.

Case 2

Right and left atrial pressures vary during inspiration and expiration. Discuss the changes in left and right atrial pressures during the respiratory cycle, and the physiological reasons why the pressures change.

Will heart rate change between inspiration and expiration? If, so during which respiratory phase will it be higher and why?

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Background:

Spaceflight is associated with a number of physiological alterations. Although astronauts do not report cardiovascular disturbances while in space, one consequence upon return to Earth is orthostatic intolerance, or an inability to remain in an upright posture while maintaining adequate perfusion of the brain. Orthostatic hypotension is a related condition in which blood pressure decreases, typically accompanied by tachycardia, during assuming an upright posture. As many as two-thirds of astronauts suffer from "post-spaceflight orthostatic intolerance," and the condition is so severe in about one-fourth of astronauts that they would be unable to escape from the landing craft if an emergency arose during landing.

Problem:

Explain the physiological changes that occur during spaceflight that result in post-spaceflight orthostatic intolerance. How does NASA protect astronauts against post-spaceflight orthostatic intolerance?

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Case 1

A 45 year-old woman is brought to the Emergency Ward by her family because they found her to be confused. Aside from longstanding use of amitryptaline for depression, she was well, taking thiazides for mild hypertension, until she developed nausea, vomiting and abdominal cramping 4 days ago, which prevented her from eating.

Physical exam reveals:

• Blood Pressure: 105/70
• Heart Rate: 100
• Respiration Rate: 18

• Patient was afebrile
• Cardiac exam was negative
• Extremities were free of edema

• Blood Chemistry:
• Na⁺ 118 mEq/L
• K⁺ 3.1 mEq/L
• Cl^- 80 mEq/L
• HCO₃^- 28 mEq/L
• S_OSM 245 mEq/L
• U_OSM 650 mEq/L

Problem

Explain the physiological reasons for the patient's confusion. How would you treat the patient's condition?

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Case 2

A 66 year-old man with no significant prior illnesses presents to the Emergency Ward complaining of feeling “out of sorts.” History is notable for 50 pack years of smoking. He was seen two weeks previously in the outpatient clinic where a routine chest X-ray was obtained, which revealed a solitary 2 cm lung nodule.

Physical exam reveals:

• Blood Pressure: 120/75
• Heart Rate: 80
• Respiration Rate: 16

• Patient was afebrile
• Cardiac exam was negative
• Extremities were free of edema

• Blood Chemistry:
• Na⁺ 188 mEq/L
• K⁺ 4.2 mEq/L
• Cl^- 153 mEq/L
• HCO₃^- 25 mEq/L
• S_OSM 385 mEq/L
• U_OSM 88.0 mEq/L

Problem:

Explain the physiological reasons for the patient's feeling "out of sorts." How would you treat the patient's condition?

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Background:

A 61-yr-old professor comes to the family physician because he feels tired all the time. He often falls asleep when he attends seminars or lectures. Although he says he sleeps through the night (except to get up to urinate), his wife says he snores loudly and often seems to stop breathing and gasp for breath. He is restless and thrashes around in bed. He almost always wakes up with a headache, and for the past year he has been having trouble remembering things. He is 5 ft 7 in. tall and weighs 250 lb. His heart rate is 80 beats/min, his blood pressure is 135/95 mm-Hg, and his respiratory rate is 15 breaths/min.

Problem:

Explain the cause of the symptoms in the patient. In addition, discuss how the results of the following tests would likely differ in this patient from a normal individual, and the reason the findings are abnormal:

• Blood pH measured when patient is awake
• Hematocrit
• Echocardiogram
• Electrocardiogram (ECG)
• Spectrometry

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Case 1

A 70 year old man was admitted with severe congestive cardiac failure. He has been unwell for about a week and has been vomiting for the previous 5 days. He was on no medication. He was hyperventilating and was very distressed. Admission biochemistry was:

• Na⁺: 127 mEq/L
• K⁺: 5.2 mEq/L
• Cl^-: 79 mEq/L
• HCO₃^-: 22 mEq/L
• pH: 7.58
• PCO₂: 21 mm Hg

Problem:

What is the patient's blood gas problem (metabolic/respiratory/mixed) and what factors are contributing to a disturbance in blood pH?

Case 2

A 35 year-old female with AIDS is brought to the emergency department with a fever of 39°C and a three month history of copious diarrhea. On physical exam the patient is a well-developed, thin female in moderate distress.

Physical Signs:

• Supine: blood pressure 100/60, pulse 100
• Standing: blood pressure 80/40, pulse 125 
• Cardiac exam demonstrated an S1 and S2 without S3, S4 or murmur
• Lungs were clear to auscultation and percussion
• The abdomen was supple and minimally tender to palpation
• Bowel sounds were hyperactive
• Neurological exam revealed no abnormal findings

• Blood Chemistry:
• Na⁺: 136 mEq/L
• K⁺: 3.4 mEq/L
• Cl^-:112 mEq/L
• pH: 7.35
• PO₂: 90 mm Hg
• PCO₂: 27 mm Hg
• HCO₃^-:14 mEq/L

Problem:

What is the patient's blood gas problem (metabolic/respiratory/mixed) and what factors are contributing to a disturbance in blood pH?

Case 3

Patients taking a loop diuretic or thiazides are at risk for metabolic alkalosis. Explain the physiological mechanism leading to a pH disturbance in patients taking these diuretics.