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Sudden Cardiac Arrest and Cardiopulmonary Resuscitation (CPR)

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  1. Introduction to sudden cardiac arrest and resuscitation
    4 Chapters
  2. Resuscitation physiology and mechanisms
    2 Chapters
  3. Causes of sudden cardiac arrest and death
    2 Chapters
  4. Cardiopulmonary Resuscitation
    10 Chapters
  5. Special Circumstances
    11 Chapters
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SCA (Sudden Cardiac Arrest): Sudden and unexpected cardiac arrest with loss of mechanical cardiac function. Results in loss of consciousness, cessation of breathing, and absence of a palpable pulse. Ventricular contraction has ceased or unable to generate perfusion.

SCD (sudden cardiac death): Death resulting from sudden cardiac arrest (SCA).

Cardiovascular collapse: Sudden cessation of tissue perfusion as a result of cardiac or vascular condition. May reverse spontaneously (e.g., vasovagal syncope) or with treatment (e.g., arrhythmias). Unconsciousness occurs within 10 seconds of cessation of cerebral blood flow.

Agonal breathing: Deep, slow, irregular breaths with a frequency of 1 to 4 breaths per minute. Agonal breathing is frequently seen during the first minute after cardiac arrest. Agonal breathing should be interpreted as cardiac arrest and cardiopulmonary resuscitation should be initiated.

Agonal breathing is interpreted as manifest cardiac arrest.

Defibrillation: Use of non-synchronized electric shock (i.e. a shock delivered randomly, without considering the phase of the cardiac cycle) to terminate ventricular fibrillation.

Cardioversion: Use of synchronized electric shock (i.e. a shock synchronized to the QRS complex). Typically used to treat atrial fibrillation, ventricular tachycardia, and other tachyarrhythmias with discernible QRS complexes.

Shockable rhythm: Tachyarrhythmias that can be treated with defibrillation (ventricular fibrillation) or cardioversion (ventricular tachycardia).

Non-shockable rhythm: Cardiac rhythm that cannot be defibrillated or cardioverted. These rhythms include pulse-less electrical activity (PEA), asystole, and bradycardia.

No-Flow: Circulatory standstill, circulatory flow arrest.

No-flow time: The duration (minutes) from circulatory collapse to initiation of CPR. During no-flow there is no cerebral perfusion and brain damage progresses rapidly.

Low-flow: The circulation (perfusion) achieved by performing CPR.

Low-flow time: The duration (minutes) from start of CPR to ROSC or end of resuscitation attempts. Efficient CPR generates approximately 25% of normal cardiac output, which postpones or mitigates cerebral injuries.

No-flow time and low-flow time are critical parameters for determining the probability of survival. No-flow longer than 6-8 minutes is mostly fatal.

Basic Life Support (BLS): CPR that can be delivered by bystanders (laypeople). BLS involves the use of chest compressions, as well as possibly ventilation and automatic external defibrillator (AED).

Return of Spontaneous Circulation (ROSC): Return of mechanical cardiac function resulting in circulation with pulse.

Coronary perfusion pressure (CPP): The pressure that drives blood flow through the coronary arteries. CPP is equivalent to the pressure difference between the aortic root and right atrium during diastole (coronary blood flow occurs in diastole or the decompression phase during CPR). High aortic pressure and low right atrial pressure favor coronary blood flow. A CPP of approximately 15 mmHg is required to induce spontaneous electrical activity in myocardial cells. CPP below 15 mmHg is insufficient to generate cardiac electrical activity.

CPP = Paortic – Pright atrium

Cerebral perfusion pressure (CerPP): The pressure that drives cerebral blood flow. CerPP is determined by intracranial pressure (ICP) and mean arterial blood pressure (MABP). Low ICP and high MABP favor cerebral blood flow.


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