LV failure is the most common cause of cardiogenic shock post acute MI but it is not the only cause:
The haemodynamic profile of patients may change over the course of their hospital admission.
- An arterial line is mandatory for both direct and possible derived values.
- Frequent measurement of lactate should be undertaken
- ScVO2 measurement is found in guidelines based on expert recommendations
- Where shock is refractory to empirical treatment, cardiac output an mixed venous oxygen saturation should be continuously monitored
- Where RV dysfunction = PAFC
- Where not, thermodilution catheter with pulse contour analysis provided no circulatory assistance (i.e. balloon pump)
- Routine use of echocardiography should be used
Assessment of cardiogenic shock follows largely clinical approach. Some new biomarkers may predict mortality in acute heart failure at 30 days more than NT-proBNP or troponin. Failure to clear lactate is associated with but may not predict outcome – this is similar to sepsis and trauma. When used in combination with adrenmedullin, a preprohormone cleaved to form two biologically active peptides of uncertain role. This appears best
Which vasopressor – Noradrenaline or Adrenaline?
Both drugs ‘toxic’ and may adversely affect myocardium with calcium overload. Noradrenaline is isotropic and lusitropic at low and high concentrations whereas adrenaline increases isotropism at low concentration and decreases it at higher concentrations.
Even at regular doses used on ICU, noradrenaline will increase cardiac work. Comparing noradrenaline to adrenaline
- MAP no difference ad = na
- HR increased ad > na
- Pulmonary pressure no data
Noradrenaline has been recommended as first line treatment to treat cardiogenic shock.
Which inotrope – Dobutamine or inodilators?
The distinction between vasopressor and inotrope is a theoretical distinction = the aim is to increase perfusion however it may need to be done
- Vasoconstriction = alpha, classically phenyl or AVP
- Inopressors = beta +/- alpha, noradrenaline, adrenaline
- Inodilators = dobutamine, PDEs, levosimendan
- Vasodilators = nitrates
Issue perfusion a function of flow and pressure. Evidence for dobutamine is poor in acute heart failure and small. Slightly better for cardiogenic shock but no firm trial data. Little reasonable evidence for levosimendan. However, too much afterload is bad.
When deciding which inotrope it may not matter… except
- Potential for complications
- Myocardial ischaemia
- Route of administration
What to do is not data driven but a thoughtful approach is helpful!
Mechanical Circulatory Support
IABP does not affect outcome and is no longer recommended following IABP-SHOCK. But what about the Impella device?
Time may be of the essence with very sick cardiogenic shock yet mechanical support with Impella or VA ECMO may be reserved until refractory. However, observational evidence from registry data is encouraging but we lack large RCTs. Aim is for LV unloading to reduce risk of pulmonary oedema which does not occur with poorly titrated ECMO. Appropriate venting is key to prevent LV stretch.