Thesis
Myocardial responses and adaptations following exercise testing and physical training in cardiac rehabilitation after myocardial infarction and coronary artery bypass surgery
Southern Cross University
Doctor of Philosophy (PhD), Southern Cross University
1997
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Abstract
The aim of this thesis was to examine myocardial responses and
adaptations following exercise testing and exercise training early after
myocardial infarction and coronary bypass surgery in the setting of a
monitored cardiac rehabilitation programme. Patients underwent exercise
testing 14 to 21 days after myocardial infarction or coronary artery bypass
grafting utilising a bicycle ergometer or treadmill using well established
protocols. On the basis of heart rates achieved during this exercise test,
moderate to high intensity exercise training was carried out under radio
telemetry monitoring using training heart rates that were a maximum of
85% and a minimum of 75% of those achieved in the initial exercise test.
Training was carried out on bicycle ergometers, treadmills, rowing
machines and upper-arm ergometer. The training was carried out for one
hour a day, four days a week over a period of six weeks. The initial study
examined the cardiac responses early after myocardial infarction and
coronary artery bypass grafting and three groups of patients were
considered:
• patients without beta adrenergic blocking therapy
• patients being treated with beta adrenergic blocking therapy
• patients immediately after bypass surgery
This study demonstrated a significant increase in functional
capacity in all groups, the greatest being in the post coronary artery
bypass grafting patients. The increase in functional capacity at six weeks
in all groups was greater after six weeks of training than control patients
achieved at six months. Exercise training was demonstrated to be safe
with no cardiac deaths during training sessions. To further address the
safety of exercise testing early after myocardial infarction a study was
undertaken to assess the effects of early exercise testing and training on
left ventricular function evaluated by radionuclide ventriculography
compared with a control group of patients. There were no differences in
resting left ventricular ejection fraction after training between training and
control patients and no indication of deterioration of left ventricular
function. Further research was then carried out to assess whether exercise
training could add diagnostic information to identify patients at risk of
further cardiac events. Patients developing angina and ST depression on
electrocardiogram were recommended for coronary angiography. The
study findings confirmed that early exercise testing and training did
identify patients who were at high risk of cardiac events in a patient group
who had been identified as low risk. Patients with angina and ST segment
depression had a high incidence of severe operable and diffuse inoperable
disease. A further finding was that some physicians had resisted the
recommendation for coronary angiography in a group of patients who
subsequently had a high mortality rate. This group of patients had less
clinical follow-up and less medication than the patients who underwent
coronary angiography. An investigation involving high risk patients with
documented poor left ventricular function found that these patients also
demonstrated a significant increase in functional capacity following six
weeks of training which was maintained but not increased over 12
months. Findings also showed a high incidence of spontaneous
ventricular arrhythmias. It was only aggressive treatment of spontaneous
and inducible arrhythmias by the use of programmed stimulation at
electrophysiology study and intensive antiarrhythmic therapy that
prevents the mortality in this study being as high as mortality reported in
other studies. Almost half of the deaths in the year after myocardial
infarction are sudden and not necessarily associated with clinical evidence
of myocardial infarction. A further study evaluated the value of
programmed electrical stimulation and exercise testing in predicting one
year mortality after myocardial infarction. This showed programmed
stimulation to be a powerful predictor of mortality and was significantly
superior in predicting death than exercise testing. Programmed stimulation
and exercise testing together predicted virtually all deaths within the first
year.
Non-Q wave myocardial infarction had been considered to be smaller and
less significant infarcts, but evidence has accumulated that non-Q wave
infarction has a greater incidence of re-infarction, post infarction angina
and increased need for coronary bypass surgery. A final study to examine
ischaemia after non-Q wave infarction was performed utilising exercise
echocardiography to assess wall motion abnormalities of the left ventricle
after exercise. This study demonstrated two significant findings: Firstly,
that there was a high incidence of multivessel disease in this group of
patients with non-Q wave infarction. Secondly, there was an unexpected
prolongation of wall motion abnormality with abnormalities lasting longer
than 20 minutes. This prolongation of ischaemia (myocardial stunning) if
repeated, is postulated to cause a chronic decrease in left ventricular
function. This could have ramifications for exercise training in cardiac
rehabilitation programmes with repeated episodes of ischaemia and
prolonged wall motion abnormalities during and after exercise sessions.
This may not have an immediate effect over the six weeks training
programme, but confidence engendered by such a programme may result
in continued mid to high intensity exercise and possible deterioration of
left ventricular function.
Conclusion
As new technology evolves, continued assessment of the safety of
early exercise testing and training after myocardial infarction and coronary
artery bypass surgery will need to be an ongoing process.
Details
- Title
- Myocardial responses and adaptations following exercise testing and physical training in cardiac rehabilitation after myocardial infarction and coronary artery bypass surgery
- Creators
- David Vincent Cody
- Contributors
- Allan Davie (Supervisor) - Southern Cross UniversityAlan Morton (Supervisor) - Southern Cross University
- Awarding Institution
- Southern Cross University; Doctor of Philosophy (PhD)
- Theses
- Doctor of Philosophy (PhD), Southern Cross University
- Publisher
- Southern Cross University
- Number of pages
- xv, 212
- Identifiers
- 991012955800502368
- Copyright
- © David V Cody 1997
- Academic Unit
- School of Health and Human Sciences; Human Sciences
- Resource Type
- Thesis