A 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: Doxazosin Avapro Tiazac Toprol Lasix Potassium supplements Digoxin Zyrtec, celebrex Her EKG records displayed several arrhythmias and while efforts at treatment were being made, she went into ventricular fibrillation.

The EKG Physiology in action

Objectives l understand basic cardiac anatomy l understand how cellular action potentials give rise to a signal that can be recorded with extracellular electrodes l understand the path for action potential propagation through the heart l understand the origin of the main phases of electrocardiogram (EKG)

The Heart is a pump has electrical activity (action potentials) generates electrical current that can be measured on the skin surface (the EKG)

Currents and Voltages l At rest, V m is constant l No current flowing l Inside of cell is at constant potential l Outside of cell is at constant potential A piece of cardiac muscle outside inside 0 mV + -

Currents and Voltages l During AP upstroke, V m is NOT constant l Current IS flowing l Inside of cell is NOT at constant potential l Outside of cell is NOT at constant potential A piece of cardiac muscle outside inside Some positive potential + - current AP An action potential propagating toward the positive ECG lead produces a positive signal

More Currents and Voltages A piece of cardiac muscle outside current + - A negative voltage reading inside An action potential propagating Away from the positive ECG lead produces a negative signal

More Currents and Voltages current A piece of totally depolarized cardiac muscle outside inside V m not changing No current No ECG signal A piece of cardiac muscle outside inside During Repolarization + - Some negative potential Repolarization spreading toward the positive ECG lead produces a negative response

The EKG l Can record a reflection of cardiac electrical activity on the skin- EKG l The magnitude and polarity of the signal depends on –what the heart is doing electrically l depolarizing l repolarizing l whatever –the position and orientation of the recording electrodes

Cardiac Anatomy Atrial muscle Sinoatrial (SA)A node Left atrium Descending aorta Inferior vena cava Ventricluar Pulmonary veins Superior vena cava Tricuspid valve Mitral valve Atrioventricular (AV) node Purkinje fibers muscle Internodal conducting tissue

Flow of Cardiac Electrical Activity SA node Atrial muscle AV node (slow) Purkinje fiber conducting system Ventricular muscle Internodal conducting fibers Atrial muscle

Conduction in the Heart s approx s SA Atria Atrial muscle SA node Left atrium Descending aorta Inferior vena cava Ventricluar Pulmonary veins Superior vena cava Tricuspid valve Mitral valve AV node Purkinje fibers muscle Specialized conducting tissue Purkinje Ventricle node AV

The Normal EKG P Q R S T Right Arm Left Leg QT PR s approx s Atrial muscle depolarization Ventricular muscle depolarization Ventricular muscle repolarization “Lead II”

Action Potentials in the Heart AV Purkinje Ventricle Aortic artery Left atrium Descending aorta Inferior vena cava Ventricluar Atrial muscle Pulmonary veins Superior vena cava Pulmonary artery Tricuspid valve Mitral valve Interventricular septum AV node SA node ECG QT PR s approx s SA Atria Purkinje fibers muscle Specialized conducting tissue

Start of EKG Cycle

Early P Wave

Later in P Wave

Early QRS

Later in QRS

S-T Segment

Early T Wave

Later in T-Wave

Back to where we started

A 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: Doxazosin Avapro Tiazac Toprol Lasix Potassium supplements Digoxin 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 Death As noted, the patient’s heart rate was irregular and so were her EKG records. The figures below show two types of patterns seen: