Download Heart dissection with context APS

Sheep heart dissection with a human disease context
Author: Nancy M. Aguilar-Roca, PhD, Ecology and Evolutionary Biology, University of
California, Irvine, Irvine, CA 92697-2525. email: [email protected]
Abstract: Dissections are considered an important activity for learning physiology, but
they are generally passive activities in which students identify and memorize structures
from a dissection manual. The primary goal of this sheep heart dissection activity is to
provide students with a real-world context in which to learn cardiovascular anatomy and
its relevance to physiological problems. Students are individually responsible for using
textbooks or online resources for learning basic anatomy on their own prior to lab. During
lab they will research types of cardiovascular diseases or disorders that are treated
surgically. Each member of a four person team will have their own surgical procedure that
they will teach to the rest of the team. As the dissection of the sheep heart proceeds,
students will take turns identifying the structures that are relevant to their surgical
protocol. The dissection can be carried out with preserved sheep plucks and/or fresh lamb
hearts from a local butcher. Follow-up activities may include predicting the consequences
of different anatomical abnormalities on cardiac function, as well as discussions of
potential complications from different surgical procedures.
Learning goals. Students will
 Appreciate the importance of learning anatomy for health-related professions
 Understand the relationship between cardiac structures and their function
Learning Objectives. By the end of this activity, students will be able to
 identify major coronary arteries
 explain what happens during a heart attack
 define stents and coronary artery bypass graft (CABG)
 identify major external anatomy landmarks used by cardiovascular surgeons
 predict the consequences of cardiac anatomical abnormalities
Materials
 Preserved hearts (e.g. from Carolina Biological Supply) and/or fresh hearts (e.g.
from a local butcher). At least one heart per group of four students
 Dissecting tools (scalpel, scissors, blunt probe, tweezers) and trays
 Packet of handouts (1 per group)
 Web access
Pre-dissection preparation
Prior to the dissection, students should create their own dissection guides using textbooks
and/or online references. In their drawings, students should include all of the structures
listed, as well as a schematic of the flow of oxygenated and de-oxygenated blood flow
through the heart. The list of structures provided here can be shortened or lengthened to fit
the level of your students.
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Aorta
Aortic valve
Atria (left & right)
Auricles (left & right)
Bicuspid (=Mitral) valve
Chordae tendinae
Coronary arteries (left, right, circumflex)
Tricuspid valve
Papillary muscles
Pericardium
Pulmonary valve
Pulmonary artery
Pulmonary veins
Vena cava (superior & inferior)
Ventricular septum
Ventricles (left & right)
Lab dissection procedure
This is designed for groups of four students. Total time required ~75min.
Each group of 4 students will be given a list of 4 cardiovascular surgical procedures.
a) coronary artery stent
b) coronary artery bypass graft (CABG)
c) ventricular septal defect repair
d) mitral valve replacement
Each student in the group will take one procedure to research prior to dissection (i.e.
surgery). Each student should
 define the disease or disorder that the surgery will treat
 list symptoms of the disease
 give an overview of the procedure
Give students ~20 minutes to research their procedure online or in textbooks, and fill-out
their worksheet. After that, give groups ~20 minutes to share what they found with each
other. Students should use their drawings to teach each other what structures are going to
be surgically accessed.
Once students have familiarized each other with the procedures, allow them to begin their
dissections. During dissection, each student should have a chance to hold the heart and be
the “head surgeon” who explains to the others which structures they will work on. During
the dissection if students go in order of handouts (a, b, c and d), they’ll proceed roughly
from least invasive to most invasive, in terms of cutting the heart.
Data collection (optional)
To make this a more quantitative activity, have each group make a set of measurements of
their heart and pool the class data for a discussion of anatomical variation. Possible
measurements:
 Maximum thickness of the left and right ventricular walls
 Estimated diameters of the aorta, left coronary artery and pulmonary artery. (Add
another quantitative analysis by asking students to estimate the resistance to flow
in each of those vessels using Poiselle’s law. What will happen to resistance in the
coronary artery if its diameter is reduced by half because of plaque?)
Potential follow-up questions & discussions. The possible post-lab questions are endless
depending on the level of your students, whether or not you did related cardiovascular
activities such as ECGs and what you want to emphasize. Here are some suggestions.
1. For patients who have these procedures, will they be expected to make any lifestyle
changes or take any drugs for the rest of their life? What are common complications?
2. Why do heart attacks affect ECGs?
When heart muscle is damaged, it’s ability to conduct electrical signals is altered which can be
seen in an ECG.
3. Read or listen to the following NPR story:
http://www.npr.org/blogs/health/2015/04/06/397281837/women-having-a-heartattack-dont-get-treatment-fast-enough.
Why are young women more likely to die of a heart attack than men?
4. In cases of severe, prolonged mitral valve regurgitation, stroke volume increases. Why?
Because some blood leaks backwards during each contraction, the heart has to contract
harder to eject enough blood into the aorta to meet demand. Overtime, the heart also
enlarges.
5. How does high blood pressure contribute to atherosclerosis?
High pressures damage the endothelium of the blood vessels in a way that causes stiffness and
encourages plaque to accumulate on the artery wall
6. How is the pressure-volume (P-V) loop from a normal patient different from the P-V
loop from a patient in congestive heart failure?
Answers will vary depending on the source.
Pattern 1: heart is enlarged, but without thickened walls. These hearts tend to have larger
end-systolic volumes and end-diastolic volumes, but pressures are near normal
Pattern 2: enlarged heart with thickened walls (ventricular hypertrophy). These hearts tend
to have much higher systolic pressures and higher end-diastolic volumes. The stroke volume
and end-systolic volume can vary depending on the severity, the duration and cause of the
heart disease
7. The following drugs affect heart rate. Go online to find out their mechanism of action and
hypothesize how they affect R-R interval, P-R interval and Q-T interval.
 Beta-blockers - longer R-R interval, longer P-R interval because it reduces A-V node
conduction
 Caffeine - shorter R-R interval. Effects on other aspects of the ECG are variable and
depend on what study the student reads.
 Calcium channel blockers - longer R-R interval, longer P-R interval because it reduces
A-V node conduction
Cardiovascular Physiology Pre-Surgery Worksheet (a)
You are going to be the lead surgeon to place a coronary artery stent. Before you begin, you
must do some research and then prepare your team.
1) What disease(s) or disorder(s) can be treated with a coronary artery stent?
2) What are the most common symptoms (or important test results) for diagnosing the
disease or disorder?
3) Briefly describe the procedure. Talk with the surgeon for the coronary artery bypass
graft (CABG) procedure about when a patient should have a stent instead of a CABG
procedure.
4) When you receive the heart, teach the procedure to your team. Be ready to help identify
all of the structures from the dissection guide you made before class.
Cardiovascular Physiology Pre-Surgery Worksheet (b)
You are going to be the lead surgeon to place a coronary artery bypass graft (CABG). Before
you begin, you must do some research and then prepare your team.
1) What disease(s) or disorder(s) can be treated with a CABG procedure?
2) What are the most common symptoms (or important test results) for diagnosing the
disease or disorder?
3) Briefly describe the procedure. Talk with the surgeon for the stent procedure about
when a patient should have a CABG procedure instead of a stent.
4) When you receive the heart, teach the procedure to your team. Be ready to help identify
all of the structures from the dissection guide you made before class.
Cardiovascular Physiology Pre-Surgery Worksheet (c)
You are going to be the lead surgeon for a mitral valve replacement. Before you begin, you
must do some research and then prepare your team.
1) What disease(s) or disorder(s) might lead to a mitral valve replacement?
2) What are the most common symptoms (or important test results) for diagnosing the
disease or disorder?
3) Briefly describe the procedure. What are the pros and cons of using a mechanical or an
artificial valve?
4) When you receive the heart, teach the procedure to your team. Be ready to help identify
all of the structures from the dissection guide you made before class.
Cardiovascular Physiology Pre-Surgery Worksheet (d)
You are going to be the lead surgeon for a ventricular septal defect repair. Before you begin,
you must do some research and then prepare your team.
1) At what stage of life is it normal to have a hole in the ventricular septum? What is the
purpose?
2) What are the most common symptoms (or important test results) for diagnosing a
ventricular septal defect?
3) Briefly describe the procedure.
4) When you receive the heart, teach the procedure to your team. Be ready to help identify
all of the structures from the dissection guide you made before class.