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52 Cardio Diabetes Medicine 2017

Cardiogenic Shock: Etiopathogenesis

and Clinical Recognition

Deep Chandh Raja, MD., DM., DNB., CARDIOLOGY
Associate Consultant
The Madras Medical Mission, Chennai

Shock is a pathophysiological state wherein there is to intra-cardiac causes of myocardial pump failure.
significant reduction in tissue oxygen delivery due Intra-cardiac causes of cardiogenic shock: Causes of
to decreased tissue perfusion. Tissue oxygen deliv- pump failure are diverse, but can be classified into
ery is maintained in an individual by adequate blood 3 categories- Cardiomyopathic, Arrythmic and Me-
volume and hemoglobin content, cardiac contractility chanical. (3)
and tissue metabolic demand. Derangement in any
of these parameters is usually compensated by one Cardiomyopathy: Myocardial infarction is one of
or more of the following mechanisms: increase in leading causes of acute cardiogenic shock. Incidence
heart rate, increase in cardiac contractility and diver- of cardiogenic shock ranges from 5-10% of patients
sion of peripheral blood to vital organs by peripheral with myocardial infarction. (4) MI involving more than
vasoconstriction and increased peripheral oxygen 40% of the left ventricular myocardium, severe ex-
extraction. tensive ischemia due to multi-vessel coronary artery
disease, severe right ventricular infarction can lead
Shock can be- Hypovolemic, Distributive, Cardiogenic to acute pump failure.
or Obstructive. The underlying mechanism of shock
(1)
varies according to the type of shock and is more of- 1. Acute decompensation of chronic heart failure:
ten an overlap of mechanisms. This is best explained Majority of chronic heart failure patients are
in a patient of sepsis with distributive type of shock those with etiologies ranging from ischemic car-
with decreased peripheral vascular resistance who diomyopathy, idiopathic dilated cardiomyopathy,
later on develops cardiogenic pump failure due to end-stage hypertrophic cardiomyopathy or end-
myocardial depression by circulating inflammatory stage restrictive cardiomyopathy. Such patients
mediators. remain in a compensated state with medications
as well as their body’s own homeostatic mech-
Definition of Cardiogenic Shock: anisms. Any deterioration in the pump function
due to progressive heart failure or arrhythmias or
Cardiogenic shock is defined by hypotension (sys-
tolic blood pressure < 90mmhg for at least 30 min- an extraneous influence like sepsis or acidosis
utes) due to a low cardiac index (<2.2 L/mt/sq.mt or renal failure (Reno-cardiac) can lead to acute
with support and <1.8 L/mt/sq.mt without support) decompensation and cardiogenic shock.
and elevated filling pressures of the left, right or both 2. Acute stunning of myocardium can occur sec-
ventricles (>18mmhg) and decreased mixed venous ondary to cardiac arrest, myocarditis, prolonged
oxygen saturation. The systemic vascular resistance cardiopulmonary bypass, sepsis or insult to the
is usually high by means of a compensatory periph- central nervous system. This can also result in
eral vascular constriction. (2) cardiogenic shock.
3. Severe right ventricular infarction secondary to
Etiology of Cardiogenic Shock: MI can lead to forward failure in the absence of
Cardiogenic shock is due to intra-cardiac or ex- congestive features in the lungs.
tra-cardiac causes of myocardial pump failure. In
the true sense the term cardiogenic shock applies

GCDC 2017