Abnormalities of the Conduction SystemElizabeth Dugan - edugan@hmc.psu.edu

Olamide Odubogun - oodubogun@hmc.psu.edu

Rhythm Of The Heart

The Heart is Like an Orchestra.It has a conducting system that is directed by a conductor.

This conductor is the “Natural Pacemaker” of the Heart

Conducting System:-SA node (Primary Pacemaker)-AV node -Bundle of His-Purkinje Fibers

•Sino-Atrial node (SA Node)

-Origination and dissemination of electrical signals to BOTH atria

-Causes BOTH atria to contract

•Atrioventricular Node (AV Node)

-Transmits signal to ventricles by going through interventricular septum

-Causes intentional delay, to allow atria to complete pumping

•His Purkinje System

-Electrical signal flows through the His-Purkinje system and causes the ventricles to contract SIMULTANEOUSLY

Conducting System

SA node fires electrical

signal spreads through the

Right and left atria Right and

Left atria contract (blood moves from atria to ventricles)

AV Node fires electrical signal

spreads through His-Purkinje

System Right & Left Ventricles

Contract (blood moves from ventricles into aorta and pulmonary a.)

Electrical Signal

The Electrocardiogram (EKG or ECG)

WHAT does an EKG measure?•Measures electrical signals from heart.

This consists of: •Atrial contraction - P Wave•Ventricular contraction – QRS complex•Ventricular Relaxation – T Wave

HOLD ON!!!!!

What about Atrial Relaxation?

HOW does it do this?Your body is a conductor of electricity

•The electrical signal generated in the heart is detected by the leads placed on the surface of the body

EKG Mechanics

Atria contract P Wave

Ventricles contract QRS complex

Ventricles Relax T Wave

Main EKG Waves

Normal EKG:1. Regular Rate –heart rate of 60-100 bpm2. Regular Rhythm – P – QRS – T – P – QRS – T – P – QRS – T - etc3. The height of the wave – related to the mass of the muscle generating the wave

- the ventricles have more mass than the atria:

- large ventricles (ventricular hypertrophy) more muscle creating a stronger signal when the ventricles contract:

Normal EKG

QRS

P PPP

QRS QRSQRS

T T T TP

P wave is smaller than QRS complex

taller QRS complex

Ventricular Hypertrophy (Large Ventricle)

Normal EKG

Causes of a Large QRS Complex

Increased mass in:1. One ventricle2. Both ventricles3. Portion of the ventricle

NOTICE the very large QRS complex in the EKG

QRS

Ventricular Fibrillation

1. Ventricular Fibrillation – disordered electrical activity

The ventricles "flutter" rather than beat and pump little or no blood.

2. In minutes, collapse and sudden cardiac death will follow

Medical help is needed immediately

3. Treatment - defibrillator

ARRHYTHMIA

-Disease of the myocardium

-Portion of the myocardium is thickened (hypertrophied, aka, the opposite of atrophy)

-Individual muscle fibers are disorganized abnormal conduction + arrhythmias

Hypertrophy is asymmetric The interventricular septum (muscle b/w

the 2 ventricles) is usually enlarged much more than the rest of the ventricle

Hypertrophic Cardiomyopathy

The ventricle is hypertrophiedWhat happens to the following:Relaxation?Filling?Pressure?Forward Flow?What does all this cause?

ALLARE

DECREASED!

Difficulty breathing!

Outflow ObstructionOutflow tract obstruction – (the outflow tract is the path from the LV into the aorta)

Increased velocity!

Normal FlowNormal Velocity, Low Pressure

Outflow ObstructionFast Velocity, High Pressure

When flow is obstructed, you need to build more muscle so that you can pump harder! This equals hypertrophy!

Mitral Regurgitation- Narrowed outflow tract =

faster flow- Faster flow of blood pulls

the mitral valve open- Blood goes back into the

atria from the ventricle during systole mitral regurgitation Left

Ventricle

AorticValve

Mitral Valve

Regurgitation

SHOW VIDEOHOW WE FIX MITRAL REGURG?

HCM Symptoms

• Average age presentation : mid 20s• Wide range symptoms/severity• Difficulty breathing (dyspnea)

–WHY?• Angina

–WHAT DOES ANGINA MEAN?• Syncope (fainting)

–FROM WHAT?–WHY WOULD FAINTING BE BENEFICIAL?

Interesting Facts– What is the most common cause of cardiac death in athletes?

• Hypertrophic Cardiomyopathy

– How many people does this affect?• 1/500

– Is everyone at risk for this? • Inherited (genetic) disorder: autosomal dominant, know

your genetics and be careful if you are a possible carrier!

– Does everyone with HCM have the same symptoms and outlook?

• There are different forms of the disease and some are more severe than others incomplete penetrance

Physical Exam

• Often are normal• Extra heart sounds

– Fourth heart sound – this is heard before the “Lub” instead of “lub-dub” you here “da-lub-dub”

• Systolic Murmur – Due to Turbulent (noisy) flow through the outflow tract (LV to Aorta)

• Systolic Murmur– Due to regurgitation of blood through the mitral valve

HCM and Arrhythmias

Normal Myocardium :

Linear arrangement

HCM: Disarray!

Physiology 101: Structure = Function

Thus, Abnormal Structure=…

During Vfib

-The ventricles are like bowl of jelly

- Inefficient pump

-Muscle cells malaligned

“Myocardial Disarray”

MYOCARDIAL DISARRAY

HHOW DO YOU SOLVE THIS PROBLEM??

1) Defribillators e.g. ICD

2) Pacemakers (artificial)

Implantable Cardioverter Defibrillator (ICD)An ICD is used in patients at risk for:1. Ventricular tachycardia (>100 bpm) 2. Ventricular fibrillation3. Sudden cardiac death caused by arrhythmiasAn ICD is made up of two parts:1. Pulse generator – battery plus circuits 2. One or two leads (wires)How the ICD Works:1. Leads monitor your heart rate2. ventricular tachycardia or fibrillation detected controlled burst of impulses (called "overdrive" pacing)3. If that does not work, the ICD "shocks" the heart to restore a normal rhythm. Newer ICD devices can also work like a pacemaker if a slow heart rate (bradycardia) occurs.

What does it Look Like???

An ICD is like a pacemaker in some ways, but it can use higher energy electrical pulses to treat certain dangerous types of arrhythmia.

Pacemakers are used to treat:1.Abnormal rates

Bradycardia/ Tachycardia2.Abnormal rhythms

ArrhythmiaAtrial fibrillation

Goals:1.Coordinate the electrical signaling between the upper and lower chambers of the heart2.Coordinate the electrical signaling between the ventricles

Pacemaker

The End