A Case of DizzinessA Case of Dizziness

A 68 year old female arrives at the emergency room in an ambulance. That evening she had been feeling “weak and dizzy” after ingesting a handful of her “heart pills” and later passed out. Her heart rate was irregular but near 33 beats per minute.

Her patient records and talks with her family revealed that she is being treated for poorly controlled hypertension and congestive heart failure. Her records indicate she has been prescribed the following medications:

DoxazosinAvapro Tiazac ToprolLasixPotassium supplementsDigoxin Zyrtec, celebrex

Her EKG records displayed several arrhythmias and while efforts at treatment were being made, she went into ventricular fibrillation.

The EKGThe EKG

Physiology in action

ObjectivesObjectives

understand basic cardiac anatomy understand how cellular action potentials

give rise to a signal that can be recorded with extracellular electrodes

understand the path for action potential propagation through the heart

understand the origin of the main phases of electrocardiogram (EKG)

The HeartThe Heart

is a pump

has electrical activity(action potentials)

generates electricalcurrent that can be measured on the skin surface (the EKG)

Currents and VoltagesCurrents and Voltages

At rest, Vm is constant

No current flowing Inside of cell is at

constant potential Outside of cell is at

constant potential

++++++++++++++++++

------------------------------

A piece of cardiac muscle

outside

inside

0 mV

+-

Currents and VoltagesCurrents and Voltages

During AP upstroke, Vm is NOT constant

Current IS flowing Inside of cell is NOT

at constant potential Outside of cell is NOT

at constant potential

++++------------------------------++++++++++++++

A piece of cardiac muscle

outside

inside

Some positive potential

+-

current

AP

An action potential propagatingtoward the positive ECG lead produces a positive signal

More Currents and VoltagesMore Currents and Voltages

A piece of cardiac muscle

outside

current

+-

A negative voltage reading

------++++++++++++++

inside

++++------------------------An action potential propagatingAway from the positive ECG lead produces a negative signal

More Currents and VoltagesMore Currents and Voltages

current

-------------------------------

A piece of totally depolarizedcardiac muscle

outside

inside

+++++++++++++++++++

Vm not changingNo currentNo ECG signal

+++++++-------------------

A piece of cardiac muscle

outside

inside

------------+++++++++++

During Repolarization

+-Some negative potential

Repolarization spreading towardthe positive ECG lead producesa negative response

The EKGThe EKG

Can record a reflection of cardiac electrical activity on the skin- EKG

The magnitude and polarity of the signal depends on– what the heart is doing electrically

depolarizing repolarizing whatever

– the position and orientation of the recording electrodes

Cardiac AnatomyCardiac Anatomy

Atrial muscle

Sinoatrial (SA)A node Left atrium

Descending aortaInferiorvena cava

Ventricluar

Pulmonaryveins

Superiorvena cava

Tricuspid valve

Mitral valve

Atrioventricular (AV) node

Purkinjefibers

muscle

Internodalconducting

tissue

Flow of Cardiac Electrical Flow of Cardiac Electrical ActivityActivity

SA node Atrial muscle

AV node (slow)

Purkinje fiberconducting system

Ventricular muscle

Internodalconductingfibers

Atrial muscle

Conduction in the HeartConduction in the Heart

0.12-0.2 s approx. 0.44 s

SA

AtriaAtrial muscleSA node Left atrium

Descending aortaInferiorvena cava

Ventricluar

Pulmonaryveins

Superiorvena cava

Tricuspid valve

Mitral valve

AV node

Purkinjefibers

muscle

Specializedconducting

tissue

Purkinje

Ventricle

node

nodeAV

The Normal EKGThe Normal EKG

P

Q

R

S

T

Right Arm

Left Leg

QTPR

0.12-0.2 s approx. 0.44 s

Atrial muscledepolarization

Ventricular muscledepolarization

Ventricular musclerepolarization

“Lead II”

Action Potentials in the HeartAction Potentials in the Heart

AV

Purkinje

Ventricle

Aortic artery

Left atrium

Descending aortaInferiorvena cava

Ventricluar

Atrial muscle

Pulmonaryveins

Superiorvena cava

Pulmonary artery

Tricuspid valve

Mitral valve

Interventricularseptum

AV node

SA node

ECGQTPR

0.12-0.2 s approx. 0.44 s

SA

Atria

Purkinjefibers

muscle

Specializedconducting

tissue

Start of EKG CycleStart of EKG Cycle

Early P WaveEarly P Wave

Later in P WaveLater in P Wave

Early QRSEarly QRS

Later in QRSLater in QRS

S-T SegmentS-T Segment

Early T WaveEarly T Wave

Later in T-WaveLater in T-Wave

Back to where we startedBack to where we started

A Case of Sudden DeathA Case of Sudden Death

A 68 year old female arrives at the emergency room in an ambulance. That evening she had been feeling “weak and dizzy” after ingesting a handful of her “heart pills” and later passed out. Her heart rate was irregular but near 33 beats per minute.

Her patient records and talks with her family revealed that she is being treated for poorly controlled hypertension and congestive heart failure. Her records indicate she has been prescribed the following medications:

DoxazosinAvapro Tiazac ToprolLasixPotassium supplementsDigoxin Zyrtec, celebrex

Her EKG records displayed several arrhythmias and while efforts at treatment were being made, she went into ventricular fibrillation.

A Case of Sudden DeathA Case of Sudden DeathAs noted, the patient’s heart rate was irregular and so were her EKG records. The figures below show two types of patterns seen: