Introduction to ECGs

Conduction System

Heart Beat

Graphic from Boston Scientific International.

Start the Heart

Now we’re going to look at what you just did.

ECG

ECG Parts

• P – Atrial depolarization (contraction)

• QRS – Ventricular depolarization (contraction – BP systole)

• T – Ventricular repolarization

(rest – BP diastole)

• U – Atrial repolarization

(rest – BP diastole)

R to R interval• The time between the R waves on two

consecutive heartbeats.

Important “Times”

• 1 small square = 0.04 second• 1 large square = 0.2 second• Atrial contraction – P-R interval (PRI) = 0.1-0.2 second• Ventricular contraction – QRS complex = 0.04-0.11 second• Always use 6 second (30 large squares) strip to analyze an ECG

waveform

• This is what I want you to remember. These squares represent a certain amount of time. This helps us determine the patient’s heart rate and regularity of heartbeat.

Now some math!

• If your heart beats 75 times per minute, how long is the R to R interval?

Answer: 0.8 seconds.

Types of heart rhythms

SinusAtrial

Ventricular

Sinus Rhythms – always have P wave followed by QRS

• Normal Sinus Rhythm (NSR) rate is

60-100 and rhythm is regular

Types of sinus rhythms

Normal Sinus Rhythm (NSR)Sinus arrhythmiaSinus bradycardiaSinus tachycardia

Sinus arrhythmia – rate is 60-100 and rhythm is irregular

Sinus bradycardia – rate is less than 60 and is usually regular

Sinus tachycardia – rate is more than 100 and less than 150 is

usually regular

Atrial Rhythms P wave and/or PR interval are

abnormal. QRS may be missing after

some P waves. QRS is always normal, if it is

present

Premature Atrial Contraction (PAC)• Rate is usually normal and may be regular except

when the PAC occurs. Some contractions have a shortened PR interval or the P wave may not be identified because it is buried in the T wave.

Atrial tachycardia (A Tach)

Rate is 150-250 and usually regular. PR interval is shorter than normal and the P wave may move up on the T wave or be buried in it (wet T). Each P wave is followed by a QRS complex.

Atrial Flutter (AF)• Rate is 250-400. P waves are usually 0.2 seconds each and

occur in clusters of 2, 3, or 4 (look like saw teeth). Each cluster is followed by a QRS complex at regular intervals. Because of this, they are classified as being AF 2:1, 3:1, or 4:1.

Atrial fibrilliation (A-Fib)• Atrial rate is too fast to count and individual P waves

may be difficult to identify. Normal QRS complexes appear at irregular intervals. There will be many more P waves than QRS complexes. May cause blood clots to form and be sent to the brain, heart or lungs.

• Atrial Fibrillation

Ventricular Rhythms – rate varies. No P wave in front of abnormally

wide QRS complexes (they will be greater than 0.1 second). It may be

difficult to identify parts as being QRST. There will be more QRS complexes than P waves in the

strip.

Premature Ventricular Contraction• Rate is usually normal and may be regular except

when PVC occurs. PVC may occur alone at regular intervals (bigeminy, trigeminy) or in clusters (salvos). If 6 or more PVCs occur in 1 minute, the heart is becoming very irritable and ventricular tachycardia can begin at any time.

Ventricular tachycardia (V Tach)

• Rate is 150-250 and regular (looks like ric rac). No P waves are seen. This is a continuous PVC run.

Ventricular fibrillation (V Fib)

• Rate is too irregular to count. Cannot identify any par of the waveform.

Asystole – Straight line

• No heart activity is seen.• Clinical death is present.• Will become biological death if lasts longer than 4-6

minutes.

This is all for now

• The rest of these slides are about heart disease and we will probably go over them at another time

Pathology of MI

• Plaque builds up slowly (frequently LAD)

• Sudden blockage occurs and muscle and nerve tissue distal begin to malfunction and then die

• Abnormal activity and contractions

• Leads to V Fib/Asystole

• Scar tissue may form during healing and cause disrhythmias.

Coronary Vessels

Plaque

Myocardial Infarction

• Heart Attack

MI Treatment

• Aimed at restoring coronary blood flow

• Angioplasty and stent placement

• Coronary artery by-pass graft (CABG)

• Anticoagulants: heparin and coumadin

• Aspirin (ASA): anticoagulant and anti-inflammatory agent

Pathology of CHF

• Congestive heart failure• Damaged valves or ventricular muscle• Heart cannot completely empty• Right failure – blood backs up in legs (pitting

edema, 1+ to 4+)• Left failure – blood backs up in lungs (pulmonary

edema)• Cardiotonic – lanoxin, digoxin (not if pulse < 60)• Diuretic - lasix

CHF

• Heart Failure

Test Your Knowledge

• Label the Parts of Your Heart

• Label Your Heart's Electrical System

• Name Your Blood Vessels

• Define Common Heart Problems