Abstract
Shock or severe cardiac failure developing in the course of
acute myocardial infarction is an ominous event with a grave
prognosis. Despite its frequent occurrence, the precise haemodynamic
alterations which occur in cardiogenic shock have not been clearly
defined. To date there is no uniform agreement about the therapeutic
management of these severely ill patients and the widely different
therapeutic measures being advocated only emphasise the uncertainty
about the precise pathogenesis of shock complicating acute myocardial
infarction.
This thesis reviews developments in the concept of myocardial
infarction and describes haemodynamic and respiratory studies in
patients with acute myocardial infarction.
The investigations show that nearly all patients with recent
myocardial infarction have abnormal cardio-respiratory function.
Even in patients with so called 'uncomplicated' myocardial infarction
cardiac output is in the low normal range and the mixed venous
oxygen saturation is reduced. A number of these patients have a
raised pulmonary arterial pressure. Mismatching of ventilation and
perfusion results in arterial hypoxia. The clinical diagnosis of
left ventricular failure is not always easy and the abnormal
cardio- respiratory function suggests that sub -clinical left
ventricular failure is a relatively common finding in acute
myocardial infarction.
In patients with cardiogenic shock or clinical left ventricular
failure, the disorders of cardiac and pulmonary function are more
marked but the similarity of the abnormalities suggests that left
ventricular failure is present in both groups. The finding of raised
pulmonary arterial pressures in the patients with cardiogenic shock
is in accord with this view. In general the more severely ill the
patient the greater is the degree of cardiac failure and respiratory
abnormality.
The thesis also documents attempts to treat the impaired left
ventricular function in cardiogenic shock by digitalis and acid-base
correction and comments on the failure of this approach.
The failure to alter the course of cardiogenic shock by
pharmacological agents is similar to the reports of many other
investigators. Pain and anxiety are present in many of these patient
and this can be relieved by opiates, but recent reports have
suggested that morphine can produce marked hypotension in patients
with acute myocardial infarction and that morphine should be used
with great caution, if at all. A detailed examination of the
circulatory effects of morphine and heroin in myocardial infarction
is presented. The results suggest that morphine is a suitable
analgesic for the relief of pain in acute myocardial infarction.
