Mechanical Circulatory Support in Cardiogenic Shock:
Mechanical circulatory support (MCS) in cardiogenic shock can be addressed in a similar fashion as medical management. Just like with medical management, MCS management must address how it improves the hemodynamic problems of cardiogenic shock. The hemodynamic issues of cardiogenic shock are decreased oxygen delivery, decreased perfusion, and increased oxygen consumption. The major benefit of MCS over medical management is that it can provide the support needed to increase oxygen delivery while significantly decreasing oxygen consumption. It does this by taking over the work of the heart and allowing the heart to rest.
Cardiogenic shock problems to be addressed:
A. Decreased oxygen delivery (Low cardiac output)
1. Increased preload
2. Decreased contractility
3. Increased afterload
B. Poor perfusion (Hypotension)
C. Increased oxygen consumption
Figure 1: Breaking Down Cardiogenic Shock Hemodynamic Problems
Additionally, mechanical circulatory support will also improve perfusion by increasing blood pressure. MCS will improve both mean arterial pressure (MAP) and cardiac output (CO) whereas most vasoactive medications typically can only do one of the two at the sacrifice of the other. This is important because MAP and CO are the two components of cardiac power. It was discussed previously that the best prognostic marker for mortality in cardiogenic shock was cardiac power; Table 1(10).
Cardiac Power (CPO) = MAP x CO / 451
Normal CPO ≥ 1.0 W
Reduced CPO < 1.0 W
CPO requiring MCS ≤ 0.6 W
Table 1: Cardiac Power and Lactic Acid vs Survival in Cardiogenic Shock
When mechanical circulatory support should be initiated?
A patient should be escalated to mechanical circulatory support when their CPO is ≤ 0.6 W or when they need two or more inotropes/vasopressors to reach goal MAP and cardiac index (CI). This is an important distinction because vasopressors and inotropes increase oxygen demand and will increase mortality if used inappropriately; Table 2(10). It is especially important for ischemic cardiogenic shock where cardiac rest is needed to maximize recovery.
Table 2: Cardiac Power and Inotropes vs Survival in Cardiogenic Shock
To help with escalating to mechanical circulatory support I have again included a table of the max dosing for inotropes and vasopressors that are appropriate. If a patient requires high doses of either inotropes or vasopressors to meet goals, the discussion for mechanical circulatory support needs to begin.
Table 3: Inotrope/Vasopressor Dosing in Cardiogenic Shock
Classifying mechanical circulatory support
Mechanical Circulatory Support is divided into left ventricular support devices, right ventricular support devices, and biventricular support.
Table 4: Mechanical Circulatory Support Devices
*VA ECMO: Veno-arterial extracorporeal membrane oxygenation
What type of mechanical circulatory support should be initiated?
A patient with a CPO ≤ 0.6 W should receive a mechanical circulatory device, but it does not determine what the best device or devices are for the patient. It is important to distinguish between isolated LV failure or RV failure and biventricular failure. Algorithms are used in many cardiogenic shock protocols and the one below is similar to others available (Figure 2). The main determinant for the left side is the pulmonary artery occlusion pressure (PAOP), or wedge pressure. A PAOP > 15 mmHg identifies that the patient has left-sided failure. The main determinant for the right side is the pulmonary artery pulsatility index (PAPi). PAPi is a calculation that involves the pulmonary artery systolic pressure (PASP), pulmonary artery diastolic pressure (PADP), and central venous pressure (CVP). A PAPi ≤ 0.9 is the determinant for initiating RV MCS.
PAPi = (PASP - PADP)/CVP
Table 5: Summary of Cardiogenic Shock Decision Points
Figure 2: Cardiogenic Shock Management Algorithm
*Hypoxia due to primary lung disease and not cardiogenic pulmonary edema
^ Decision for venting/unloading the LV should be considered on all patients
Part 3c: Left Ventricular Mechanical Circulatory Support Devices (LV MCS)
Part 3d: Right Ventricular Mechanical Circulatory Support Devices (RV MCS)
Part 3e: Biventricular Mechanical Circulatory Support Devices (BiV MCS)
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