Cardiogenic Shock

Cardiogenic shock is failure of the heart to deliver enough output to meet tissue demand despite adequate filling pressure. Typical definitions are a systolic pressure under 90 mmHg for over 30 minutes (or a need for vasopressors to keep it above 90), with signs of hypoperfusion, a cardiac index under 2.2 L/min/m2 and a wedge pressure over 15 mmHg. Lactate is usually over 2 mmol/L.

Acute myocardial infarction causes about 80% of cases, mostly large anterior infarcts, and shock complicates 5 to 10% of ST-elevation infarctions.

Other causes

• Mechanical complications of infarction (papillary muscle rupture, ventricular septal rupture, free wall rupture)
• Decompensated chronic heart failure and acute fulminant myocarditis
• Takotsubo cardiomyopathy, severe valve disease and prosthetic valve thrombosis
• Sustained arrhythmia, post-cardiotomy failure and right ventricular infarction

Mechanism is a spiral: reduced output lowers coronary perfusion, which worsens ischemia, then inflammatory cytokines and nitric oxide add vasodilation and systemic organ injury. Severity is graded in stages from "at risk" through "beginning", "classic", "deteriorating" and "extremis". In-hospital mortality is 40 to 50%, higher with refractory shock, cardiac arrest and mechanical complications. Complications: acute kidney injury, ischemic hepatitis, ventricular arrhythmia, bowel ischemia, stroke and multiorgan failure.

• Cold, clammy, mottled skin, weak thready pulse, narrow pulse pressure and tachycardia
• Oliguria under 0.5 mL/kg/h, confusion, agitation and drowsiness
• Dyspnea with crackles, raised jugular venous pressure, a third heart sound and peripheral edema
• New holosystolic murmur (mitral regurgitation or septal rupture) or muffled heart sounds
• Right ventricular infarction: raised jugular pressure with clear lungs and hypotension
• Red flags: lactate over 4 mmol/L, anuria, ventricular arrhythmia, new murmur and cardiac arrest

1. 12-lead ECG within 10 minutes: ST elevation, new left bundle branch block, posterior infarction (add leads V7 to V9), right-sided leads in inferior infarction, and arrhythmia.
2. Bedside echocardiography is the first imaging test: left and right ventricular function, regional wall motion, valve regurgitation, ventricular septal defect, pericardial effusion, and tamponade.
3. Laboratory tests: high-sensitivity troponin, lactate (repeat every 2 hours), creatinine, liver tests, natriuretic peptide, glucose, blood gases, full blood count and coagulation.
4. Chest radiograph: pulmonary edema and heart size.
5. Emergency coronary angiography whenever an acute coronary syndrome is possible.
6. Arterial line, and pulmonary artery catheter in uncertain or refractory cases: cardiac index under 2.2, wedge pressure over 15 mmHg and cardiac power output under 0.6 W.

Differentials: septic and hypovolemic shock, pulmonary embolism, tamponade, aortic dissection, tension pneumothorax and acute valvular catastrophe.

1. Immediate care: transfer to intensive care, continuous monitoring, oxygen for saturation under 90%, and non-invasive ventilation for pulmonary edema. When intubation is needed use ketamine 1 mg/kg IV or etomidate 0.3 mg/kg IV, with norepinephrine running first, since induction drugs can cause collapse.
2. Vasopressor: norepinephrine 0.05 to 0.5 micrograms/kg/min IV to a mean arterial pressure of 65 mmHg or higher. Avoid dopamine because of arrhythmia.
3. Inotrope for low output: dobutamine 2.5 to 20 micrograms/kg/min IV. Alternative or addition: milrinone 0.375 to 0.75 micrograms/kg/min IV without a loading dose (reduce in renal impairment, and watch for hypotension). Epinephrine 0.02 to 0.2 micrograms/kg/min IV for refractory cases.
4. Revascularization: emergency percutaneous coronary intervention of the culprit artery. Surgical revascularization for left main or multivessel disease not suitable for stenting. Give aspirin 300 mg orally or chewed once, then 75 mg daily, and unfractionated heparin 70 to 100 units/kg IV bolus.
5. Congestion: furosemide 40 to 80 mg IV once blood pressure is supported, repeated by urine response. Avoid nitrates, beta blockers, ACE inhibitors and morphine in the first phase.
6. Right ventricular infarction: IV 0.9% saline 250 to 500 mL cautiously, avoid nitrates and diuretics, and restore atrioventricular synchrony.
7. Arrhythmia: synchronized cardioversion for unstable tachycardia, and amiodarone 150 mg IV over 10 minutes, then 1 mg/min for 6 hours, then 0.5 mg/min. Temporary pacing for high-grade block.
8. Mechanical circulatory support for refractory shock: percutaneous left ventricular assist device or venoarterial extracorporeal membrane oxygenation, as a bridge to recovery, transplant or durable device. Routine intra-aortic balloon pumping is not advised.
9. Mechanical complications: urgent surgical repair, with balloon pump or support as a bridge.
10. Myocarditis, takotsubo and others: supportive care and mechanical support, with treatment of the cause.
11. Kidney injury: renal replacement therapy for hyperkalemia, acidosis or overload.

After recovery start evidence-based heart failure therapy gradually (ramipril 1.25 mg twice daily, carvedilol 3.125 mg twice daily, eplerenone 25 mg daily, an SGLT2 inhibitor), repeat echocardiography at 6 to 12 weeks, offer cardiac rehabilitation, and implant a defibrillator if ejection fraction remains 35% or lower after 40 days. Counsel on prognosis.