Mechanism of death: there’s more to it than sudden cardiac arrest

The dying process begins with the loss of function of one or more of the three classic vital organs: heart, brain, lungs. Failure to resuscitate the function of the affected primary organ results in cessation of function of the others. In ventricular fibrillation (VF), for example, the process occurs rapidly as the disorganized activity of the fibrillating heart produces cessation of circulation, which in turn causes loss of consciousness and respiratory drive within seconds. VF, therefore, is primary cardiac arrest; the heart causes the vasculature, brain and lungs to fail. In contrast, pulseless electrical activity (PEA) emerges with collapse of the vascular system, which is a common version of decompensation but rarely discussed in resuscitation literature. The vascular system, therefore, should be viewed as a fourth vital system. Typically, the brain and lungs fail in a sequence that may be so closely linked in time that the first organ to fail is often unclear. As the organism enters death, the heart continues to pump until the oxygen and metabolic substrates required for cardiac function are sufficiently depleted that hypotension and bradycardia emerge, which is followed by loss of an effective pulse. The loss of pulse is the initiation of PEA, but pumping continues when assessed by arterial line or echocardiography (so-called pseudo-PEA) and fades over time (minutes) through PEA to asystole. PEA is not primary cardiac arrest, but is, instead, a late stage in a process of dying that most likely began as arrest of brain, lungs and/or the vascular system. The various patterns of organ failure are delineated and described as mechanisms of dying (Figure 1)