Activation and Repolarization

OverviewOctober 2008

Heart is an “Electrically” Controlled Pump

All normal ECG waveforms result from coordinating the pump• coordinating contraction of the pump

(QRS complex)• coordinating relaxation of the pump (ST

segment/T wave/U wave)

0 50 100 150 200 250900

950

1000

1050

1100

1150

contract

hold relax

Contraction Sequence

Inside of the heart contracts inwards • known as circumferential shortening

Diastole End Systole

Contraction Sequence

And longitudinally

Diastole End Systole

Contraction Sequence

Then, outside of the heart twists/wrings

Contraction Sequence

In addition to the inside outside sequence, there is • an anterior posterior sequence • apical (bottom) basal (top) sequence

Relaxation Sequence

(Mostly) opposite to contraction Outside of the heart untwists

• associated with rapid suction of blood back into heart

Then inside of the heart relaxes Basal (top) to apical (bottom)

relaxation However, the anterior posterior

contraction sequence is the same (not opposite) as the relaxation sequence

Electrical Sequences

Follow (cause!) mechanical sequences

Electrical activation (depolarization) of the heart is from the inside out

Repolarization of the heart is from the outside in (T wave)

Activation

TOP

MID

BOT

In vivo canine heart

Wigger’s Diagram

Heart Cells and Dominoes

Dominoes all standing = no current

V=0+ -

Heart Cells and Dominoes

They start falling – current flows

V=5+ -

Heart Cells and Dominoes

All down – no current flows

V=0+ -

Heart Cells and Dominoes

Some start standing – current flows

V=5+ -

Heart Cells and Dominoes

Notice that voltage depends on wherewe measure

V=-5 +-

What about activation potentials?

Before wave reaches epi.

After wave reaches epi. - simulations

What about activation potentials?

Activation & Repolarization

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