Types of heart rhythms:
- Ventricular Tachycardia (VT, V-Tach)
Cardiac conduction orginates from reentrant circuits in
the ventricles. The heart rate is usually fast and the rhythm
is regular. The heart may or may not (pulseless VT) be able
to eject blood to the body. An AED cannot tell the difference
between the two. Shock may be advised, but should only be
given if the victim does not have a pulse (pulseless VT).
- Ventricular Fibrillatio (VF, V-Fib)
Cardiac conduction orginates from chaotic foci in the ventricles.
The heart rate is fast and the rhythm is chaotic. The heart
is not able to eject blood to the body (always pulseless).
An AED may confuse fine VF and asystole because both can
be somewhat flat. In the case of VF, shock should be advised
- Asystole ("Flat-Line")
There is no electrical activity and the electrocardiogram
shows a "flat-line". The heart is not able to
eject blood to the body (always pulseless). Shock is not
advised. CPR and advanced cardiac life support are required.
- Bradycardia ("Brady")
The heart rate is slow and the rhythm may be regular or
irregular. The heart's ability to eject blood to the body
may or may not be impaired. Advanced cardiac life support
is required as well as CPR if there is no pulse.
- Pulseless Electrical Activity (PEA)
Formerly known as electro-mechanical dissociation (EMD).
Cardiac conduction is present and the electrocardiogram
may be normal. However, the heart is not able to eject blood
to the body for other reasons. CPR and advanced cardiac
life support are required.
85% of pulseless victims are either in VF or pulseless VT.
Only 15% of pulseless victims are in asystole, brachycardia,
Why is it important to defibrillate early? When defibrillation
is done within the first minute, survival is close to 90%.
After the first minute, survival decreases by 2-10% per minute.
After 10 minutes, chances of survival are almost nil. Performing
CPR while waiting for defibrillation improves these odds.
However, early defibrillation remains the critical step to
In 2005, the American Heart Association modified their guidelines
regarding defibrillation. The old guidelines suggested performing
up to 3 shocks in succession in patients with VF or pulseless
VT. The new guidelines have reduced this to 1 shock to minimize
the time wasted during shocking sequences and maximize the
time performing CPR. Resuming CPR immediately after the first
shock circulates blood to the heart and potentiates the effect
of the shock.
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