Pathophysiology Pathophysiology

ST Elevation Myocardial Infarction - STEMI

Early recognition and differentiation of ischaemic chest pain is important. The Cardiac Society of Australia and New Zealand (CSANZ) & The National Heart Foundation of Australia ACS Treatment Algorithm  [#national-heart-foundation-of-australia.-2011] identifies this pathway in a stepwise process.

When someone presents with symptoms consistent with ACS they should immediately have an ECG, followed by a clinical medical assessment. All patients need to be given oral aspirin150-300mg if ACS is suspected and there are no contra-indications.

If they meet the criteria for reperfusion, then dependant on their location and access to a cardiac catheter lab, and time from onset of symptoms, they should receive fibrinolysis or percutaneous coronary intervention (PCI).

ECG Criteria for STEMI:

Persistent ST elevation in two contiguous chest lead of >2mm, OR
Two contiguous limb leads of >1mm, OR
New left bundle branch block (LBBB) pattern

Non-ST Elevation Acute Coronary Syndrome – NSTEACS

When someone presents with minor or no ECG changes a careful clinical history should be taken which includes, assessment of cardiovascular risk factors and history of current symptoms. Further assessments include, physical assessment, ECG, CXR and high sensitivity troponin, among other blood tests.

Patients will be stratified as being low, intermediate or high risk according to their troponin levels, clinical presentation and risk factor profile.

To facilitate this risk stratification assessment of troponin levels may be required at 3 hours and up to 6 hours from presentation, if initially negative.

A positive troponin test supported by clinical history in the absence of other causes for elevated troponin, is strongly suggestive of acute myocardial infarction (MI) – high risk ACS.

A negative troponin test throughout this time frame in the absence of ongoing symptoms suggests a low risk category, and these patients will be referred for coronary artery disease ‘rule-out’, through exercise stress testing.

For further information on low, intermediate and high risk NSTEACS refer to the ACS treatment algorithm pathway.

  • Cardiac Rehabilitation

All patients eligible for cardiac rehabilitation should be given the opportunity to enrol in a cardiac rehabilitation  program during or shortly after their stay in hospital. Cardiac rehabilitation aims to slow or reverse disease progression and to optimise functioning by providing physical, mental and social support and improving health behaviours.

Cardiovascular risk factor education is provided in a way that motivates patients and enables them to self-manage their lifestyle risks and identified needs for change. [#woodruffe-s-neubeck-l-clark-ra-et-al.-2015]

Effective strategies to manage patients with ACS include:

The most common indications for adults undergoing cardiac surgery are coronary artery and valve disease. These procedures are usually aimed at revascularisation or improving valve function.

While the majority of revascularisation procedures are completed percutaneously, CABG surgery is preferred for multi-vessel CAD, disease of the left main coronary artery, as well as for diffuse disease not amenable to PCI. Heart valve disease is either stenotic or regurgitant with  the aortic and mitral valves most commonly affected.  

i. Cardiac surgery via a median sternotomy

A median sternotomy involves the surgical division of the sternum to gain access to the heart.  This procedure is commonly used for CABG surgery and valve repairs or replacements.

A sternotomy can be full (involving a 20-25 cm incision to split the entire sternum) or partial (involving a 10-13 cm incision splitting the upper third of the sternum).

Post-operative complications may include:

ii. Minimally invasive cardiac and percutaneous coronary interventions

Minimally invasive cardiac surgery and PCIs are less traumatic than surgery via median sternotomy. There are usually fewer complications, faster recovery, hospital stays tend to be shorter and patients are able to return to usual functional activities more quickly. 

See information on Percutaneous coronary interventions for revascularisation and valve replacement.

For more information on minimally invasive cardiac surgical procedures see http://www.hopkinsmedicine.org.

Following an initial diagnosis, all attempts should be made to identify the cause of HF, as this may influence management. The table below lists some examples of potential treatment options to assist management following initial diagnosis.

Table 1: Management of heart failure causes and related conditions

Potential causes and related conditions Considerations for management
Coronary artery disease Consider revascularisation (e.g., PCI, CABG)
Valvular disease Consider valve repair/replacement
Arrhythmia (e.g., AF)

Medication management to restore and maintain sinus rhythm
Electrical cardioversion may be required episodically for those with AF who show symptomatic deterioration
AF ablation may be considered for those with medication resistant AF

Ventricular arrhythmias Implantable cardioverter defibrillator(See Implantable devices)
Diabetes Optimise glycaemic control
Hyper or hypothyroidism Optimise thyroid function
Medication induced (e.g., anthracyclines) Review and appropriately modify medication management 
Alcohol related  Encourage abstinence from alcohol
Anaemia Optimise management
Pregnancy Consider timing of delivery of baby (See Pregnancy and cardiomyopathy booklet)

 

All patients with symptoms of HF, regardless of aetiology, should be considered for enrolment into a HF disease management program. [#national-heart-foundation-of-australia-and-the-cardiac-society-of-2011]  See Models of care.

Effective strategies to support patients with HF and to prolong life include:

Other treatment options

For patients with advanced HF, additional treatment options that may be considered include ventricular assist devices or cardiac transplantation.

Ventricular assist devices (VADs)

VADs augment cardiac output in patients with severe end-stage HF. They have historically been employed as a temporary ‘bridge to a cardiac transplantation’ but in some countries, a number of devices have now been approved as lifelong ‘destination therapy’. The set up for a VAD is shown in the diagram below.

Figure 1: Left ventricular assist device installation and setup

Cardiac transplantation

Cardiac transplantation is considered for those patients with severe HF who have chronic symptoms despite maximal medical therapy.

Conditions where cardiac transplantation might not be considered include:

  • Active infection
  • Cancer
  • Irreversible pulmonary hypertension
  • Severe diabetes
  • Multi-organ disease or significant co-morbid disease
  • Advanced age
  • Non-compliance with medication and care plan
  • Drug / tobacco / alcohol abuse