Chapter 15. Cardiovascular emergencies
Ischaemic heart disease is the most common cardiovascular problem in the UK. Approximately one in four men and one in five women die from the disease. Acute manifestations of ischaemic heart disease are dealt with together under the term Acute Coronary Syndrome (ACS). Myocardial infarction (where prolonged ischaemia is causing irreversible damage to the myocardium) should be identified because reperfusion can be achieved by thrombolysis or by primary angioplasty. The factors that contribute to the development of ischaemic heart disease include:
• Cigarette smoking
• High blood cholesterol levels
• Hypertension
• Diabetes
• Family history
• Obesity.
The association of two or more risk factors greatly increases the chance of developing ischaemic heart disease. Cardiovascular events may still occur in individuals without identifiable risk factors. Ischaemic heart disease occurs when the supply of oxygenated blood to the heart is insufficient for the demands of the myocardium.
Ischaemic cardiac pain
Angina pectoris
• The discomfort of angina is caused by reversible myocardial ischaemia and usually occurs during conditions of increased oxygen demand in the presence of a fixed supply, most typically during physical exertion or mental and emotional stress
• When the patient ceases the activity and rests, the discomfort passes off rapidly (within 2–3 minutes)
• Patients with angina often describe a feeling of tightness in the chest (‘like a tight band’) or liken the discomfort to a weight on the chest
• The pain is felt retrosternally (behind the sternum) and may radiate across the chest, spreading into the arms
• In some patients, the pain may also radiate into the throat or jaw.
Acute coronary syndrome (unstable angina)
• The term unstable angina is used to describe a rapidly progressive, deteriorating pattern of angina often occurring in patients whose angina has been previously stable
• The patient’s exercise tolerance is reduced and ischaemic pain occurs more frequently
• The consumption of glyceryl trinitrate is often increased
• Ischaemic pain occurring at rest or on only minor exertion is a particularly worrying feature
• Unstable angina is a medical emergency and most patients are admitted to hospital for investigation and treatment, as there is a high instance of subsequent myocardial infarction.
Myocardial infarction
• The pain of myocardial infarction is similar in nature, site and distribution to that of angina, although it usually persists longer and is associated with more profound extra effects, such as profuse perspiration, dizziness and nausea and vomiting
• The intensity of the pain is not a reliable indicator of the immediate risk to the patient
• Only about half those with acute myocardial infarction will have a history of previous heart disease
• In elderly people and diabetics, pain may be absent (the ‘silent’ MI).
Myocardial infarction
The effects of an MI depend on the extent and location of the muscle loss, as well as on the pre-existing state of the myocardium.
The complications of myocardial infarction (see box 15.1) may be difficult to diagnose prehospital. Electrical effects are easier to diagnose using prehospital cardiac monitoring and indeed, are more commonly seen early in the course of the acute coronary event. Ischaemic and infarcted myocardial segments are electrically unstable and prone to ventricular fibrillation or tachycardia, both causes of cardiac arrest and sudden cardiac death. Atrial fibrillation also may occur which leads to a further reduction in cardiac output and an increase in risk of intracardiac thrombosis and peripheral embolisation. Interruption in the blood supply of the sinus node or atrioventricular node is a cause of bradycardia and degrees of heart block.
Box 15.1
• Cardiogenic shock – systolic output is reduced so that major organs are underperfused
• Mitral regurgitation – papillary muscles rupture causing an incompetent valve
• Cardiac tamponade – the myocardium ruptures and blood enters the pericardium
• Ventricular septal defect – the myocardium ruptures between the ventricles.
Diagnosis
• The diagnosis is made by combining the history and examination with the findings on ECG
• The patient will be anxious, pale, sweaty and may be complaining of severe chest pain, nausea and may be short of breath
• A tachycardia is likely, hypotension is an ominous sign
• Pulmonary oedema may have developed
• The 12-lead ECG may show ST segment elevation (an ‘ST elevation MI’), which will give information about which area of the myocardium is affected.
Treatment
• Sit the patient up, give them high flow oxygen, put them on cardiac monitoring and establish intravenous access as a precaution in the first instance
• Record a 12-lead ECG at the earliest opportunity, if available
• Morphine should be given; as well as providing analgesia it will have the effect of reducing myocardial demand and improving coronary blood flow
• An antiemetic should be given, both to reduce the effects of the MI and the effects of the morphine (avoid cyclizine, which may produce vasoconstriction)
• Sublingual GTN may improve the patient’s pain (only give if the systolic blood pressure is >90 mmHg). GTN reduces the workload of the heart as well as causing the coronary arteries to dilate. Sublingual administration of 0.4–0.8 mg is either by tablet or spray
• Unless contraindicated, all patients with acute coronary syndrome (ACS) or suspected myocardial infarction (MI) will benefit from 300 mg aspirin orally (contraindications include active peptic ulcer disease, bleeding disorders or allergy to aspirin)
• Consider thrombolysis dependent on local protocols.
• Address complications such as arrhythmias or pulmonary oedema
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