Cardiogenic Shock

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management | Patient Advice

Definition

Cardiogenic Shock is a life-threatening condition characterised by inadequate cardiac output, leading to insufficient oxygen delivery to tissues and end-organ dysfunction. It often occurs as a complication of acute myocardial infarction (heart attack).

Aetiology

Common causes include:

• Acute Myocardial Infarction (MI): The most common cause, often due to extensive damage to the left ventricle.
• Arrhythmias: Ventricular tachycardia or fibrillation leading to reduced cardiac output.
• Valvular Abnormalities: E.g., acute mitral regurgitation or aortic stenosis.
• Cardiomyopathies: Severe forms of dilated or hypertrophic cardiomyopathy.
• Cardiac Tamponade: Compression of the heart due to fluid accumulation in the pericardium.

Pathophysiology

Cardiogenic shock occurs due to the following mechanisms:

• Reduced Contractility: Extensive damage to the myocardium impairs the heart’s ability to pump blood.
• Compensatory Mechanisms: Activation of the sympathetic nervous system and renin-angiotensin system increases heart rate and vascular resistance, worsening cardiac output.
• End-Organ Dysfunction: Inadequate oxygen delivery leads to tissue hypoxia and metabolic acidosis.

Risk Factors

Key risk factors include:

• Large myocardial infarctions.
• History of heart failure or cardiomyopathy.
• Advanced age.
• Diabetes or chronic kidney disease.
• Arrhythmias or recent cardiac surgery.

Signs and Symptoms

Symptoms of cardiogenic shock include:

• Hypotension: Systolic blood pressure <90 mmHg.
• Tachycardia: Rapid heart rate as a compensatory response.
• Cold, Clammy Skin: Due to peripheral vasoconstriction.
• Oliguria: Reduced urine output, indicating renal hypoperfusion.
• Altered Mental State: Confusion or agitation due to cerebral hypoxia.

Investigations

Key investigations and common positive findings include:

• 12-Lead ECG: Identifies acute myocardial infarction, arrhythmias, or signs of left ventricular strain.
• Blood Tests:
  • Cardiac Troponins: Elevated in myocardial infarction.
  • Arterial Blood Gas (ABG): Metabolic acidosis and hypoxia may be present.
  • Renal Function Tests: Elevated creatinine and urea indicate renal hypoperfusion.
• Echocardiography: Shows reduced ejection fraction, wall motion abnormalities, or valvular dysfunction.
• Chest X-ray: Pulmonary oedema or cardiomegaly may be seen.
• Right Heart Catheterisation: Measures elevated pulmonary capillary wedge pressure, confirming cardiogenic shock.

Management

1. Primary Care Management

• Immediate Stabilisation: Administer oxygen to improve tissue oxygenation.
• Urgent Referral: Call emergency services for immediate transfer to a hospital.

2. Secondary Care Management

• Revascularisation: Percutaneous coronary intervention (PCI) to restore blood flow in myocardial infarction. Performed by interventional cardiologists.
• Mechanical Circulatory Support: Devices such as intra-aortic balloon pumps (IABP) to offload the heart.

3. Specialist Procedures

• Extracorporeal Membrane Oxygenation (ECMO): Used for severe cases to provide oxygenated blood directly. Performed by a specialist cardiothoracic team.
• Cardiac Surgery: For valve repair or bypass grafting if indicated, performed by cardiothoracic surgeons.

Patient Advice

Key advice includes:

• Seek medical attention immediately for symptoms like severe chest pain, breathlessness, or confusion.
• Adhere to prescribed medications, especially for underlying conditions such as heart failure or hypertension.
• Maintain regular follow-ups with cardiology to monitor heart function.