<Tr> <Td> Bystander compression - only resuscitation </Td> <Td> - </Td> <Td> 13% </Td> <Td> </Td> </Tr> <Tr> <Td> Bystander conventional CPR </Td> <Td> - </Td> <Td> 8% </Td> <Td> </Td> </Tr> <P> CPR serves as the foundation of successful cardiopulmonary resuscitation, preserving the body for defibrillation and advanced life support . Even in the case of a "non-shockable" rhythm, such as pulseless electrical activity (PEA) where defibrillation is not indicated, effective CPR is no less important . Used alone, CPR will result in few complete recoveries, though the outcome without CPR is almost uniformly fatal . </P> <P> Studies have shown that immediate CPR followed by defibrillation within 3--5 minutes of sudden VF cardiac arrest dramatically improves survival . In cities such as Seattle where CPR training is widespread and defibrillation by EMS personnel follows quickly, the survival rate is about 20 percent for all causes and as high as 57 percent if a witnessed "shockable" arrest . In cities such as New York, without those advantages, the survival rate is only 5 percent for witnessed shockable arrest . </P>

What is the most important element for successful cpr