Facts about Heart and ECG for Nurses

This is an eye opener for nurses who are preparing for various staff nurse exams. We will go through important points to be studied in the topic of human heart as well as ECG. Lets start

Heart and ECG for Nurses

Parts of Heart

2 upper chambers – Right and Left Atria

2 Lower Chambers – Right and Left Ventricle

2 Atrioventricular Valves (Mitral and Tricuspid)

– Opens with Ventricular Diastole
– Closes with Ventricular Systole

2 Semi lunar Valves (Aortic and Pulmonic)

– Open with ventricular systole

– Open with Ventricular Diastole

Circulation in Heart

Pulmonary Circulation – Unoxygenated – right side of heart

Systemic Circulation – Oxygenated – Left Side of heart

Anatomy of Coronary Arteries

2 major vessels of the coronary circulation

– Left Main Coronary Artery
– Left Anterior Descending and Circumflex branches

– Right Main Artery

– Left and right coronary arteries originate at the base of the aorta from the openings called Coronary ostia behind the aortic valve leaflets

Physiology of Blood Flow

The Cardiac Cycle

Represents the actual time sequence between ventricular contraction and ventricular relaxation

Systole – Simultaneous contraction of the ventricles

Diastole – Synonymous with ventricular relaxation When ventricles fill passively from the atria to 70% of blood capacity

Stroke volume (SV)
Volume of blood being pumped out of ventricles in a single beat or contraction
Normal stroke volume is 60 – 130 mL

Cardiac output (CO)
Amount of blood pumped by the left ventricle in one minute
Normal cardiac output is 4 – 8 L/min

Cardiac Output = Stroke Volume x Heart Rate

(Pre-load – Volume and stretch of the ventricular myocardium at the end of diastole

After-load – Amount of pressure against which the left ventricle must work during systole to open the aortic valve (Clinically measure by systolic blood pressure)

Normal Electrical Conduction System

Consists of
– SA node
– Inter-nodal pathways
– AV node
– Bundle of his
– Left & Right bundle branches
– Purkinje fibers

Electro Cardio Gram Wave form

Explaining parts of ECG

The ECG Paper

Paper divided into small squares:
▪ Width = 1 millimeter (mm)
▪ Time interval = 0.04 seconds
▪ 1 small square = 0.04 seconds

Darker lines divide paper into every 5th square vertically and horizontally:
▪ Large squares measure 5 mm in height and width
▪ Represents time interval of 0.20 seconds
▪ 25 small squares in each large square
▪ 1 large square = 0.20 seconds

The Five Step Approach of Reading an ECG

The five-step approach, in order of application, includes analysis of the following:
1. Heart rate
2. Heart rhythm
3. P wave
4. PR interval
5. QRS complex

1. How to Calculate Heart Rate from ECG?

▪ Count the number of electrical impulses as represented by PQRST complexes conducted through the myocardium in 60 seconds (1 minute)
▪ Atrial rate: Count the number of P waves
▪ Ventricular rate: Count the number of QRS complexes

There are 2 methods to determine Heart Rate. They are

The 6 second method
▪ Denotes a 6 second interval on EKG strip
▪ Strip is marked by 3 or 6 second tick marks on the top or bottom of the graph paper
▪ Count the number of QRS complexes occurring within the 6 second interval, and then multiply that number by 10

Using rate determination chart
▪ More accurate calculation of HR
▪ Preferred method
▪ Must use this method for the test

2. Interpreting ECG Rhythm

What is a Rhythm?
A sequential beating of the heart as a result of the generation of electrical impulses

Heart Rhythm can be Classified as:
▪ Regular pattern: Interval between the R waves is regular
▪ Irregular pattern: Interval between the R waves is not regular

A regular ECG Rhythm

▪ Measure the intervals between R waves (measure from R to R)
▪ If the intervals vary by less than 0.06 seconds or 1.5 small boxes, the rhythm is considered to be regular

▪ If the intervals between the R waves (from R to R) are variable by greater than 0.06 seconds or 1.5 small boxes, the rhythm is considered to be irregular

3. Analysis of P wave

▪ P wave is produced when the left and right atria depolarize
▪ First deviation from the isoelectric line
▪ Should be rounded and upright
▪ P wave is the SA node pacing or firing at regular intervals
▪ This pattern is referred to as a sinus rhythm

What do you need to think of P waves?

1. Are P waves present?
2. Are P waves occurring regularly?
3. Is there one P wave present for every QRS complex present?
4. Are the P waves smooth, rounded, and upright in appearance, or are they inverted?
5. Do all P waves look similar?

4. Analysis of PR interval

Measures the time interval from the onset of atrial contraction to onset of ventricular contraction
Measured from onset of P wave to the onset of the QRS complex
Normal interval is 0.12–0.20 seconds (3-5 small squares)

Questions to think of PR Interval?

1. Are the PR intervals greater than 0.20 seconds?
2. Are the PR intervals less than 0.12 seconds?
3. Are the PR intervals consistent across the EKG strip?

5. What you should know about QRS Complex?

The QRS complex presents depolarization or contraction of the ventricles

Q wave – First negative or downward deflection of this – large complex

R wave – First upward or positive deflection following the P wave (tallest waveform)

S wave – The sharp, negative or downward deflection that follows the R wave

Normal interval is 0.06-0.12 seconds (1 ½ to 3 small boxes)

Questions to think of QRS Complex?

1. Are the QRS complexes greater than 0.12 seconds (in width)?

2. Are the QRS complexes less than 0.06 seconds (in width)?

3. Are the QRS complexes similar in appearance across the EKG strip?

U – Wave

▪ Usually not visible on EKG strips
▪ If visible, typically follows the T wave
▪ Appears much smaller than T wave, rounded, upright, or positive deflection is they are present
▪ Cause or origin not completely understood
▪ May indicate hypokalemia

Atrial Rhythms

When the sinoatrial (SA) node fails to generate an impulse; atrialctissues or internodal pathways may initiate an impulse

The 4 most common atrial arrhythmias include:
• Atrial Flutter (rate varies; usually regular; saw-toothed)
• Atrial Fibrillation (rate varies, always irregular)
• Supraventricular Tachycardia (>150 bpm)
• Premature Atrial Complexes (PAC’s)

1. Atrial Flutter

Atrial flutter is a coordinated rapid beating of the atria. Atrial flutter is the second most common tachyarrhymia.

In Atrial Flutter, Normal P waves will be absent, Flutter Waves (F waves) will be present, ECG will have a saw tooth pattern and Rate will be around 250 – 400 bpm

Medical Treatment
▪ Cardioversion – treatment of choice
▪ Antiarrhymics such as procainamide to convert the flutter
▪ Slow the ventricular rate by using diltiazem, verapamil, digitalis, or beta blocker
▪ Heparin to reduce incidence of thrombus formation

Nursing Management

▪ Assess Patient
▪ O2 if not already given
▪ Start IV if not already established and hang NS
▪ Notify Medical Team

▪ Prepare for cardioversion

2. Atrial Fibrillation

The electrical signal that circles uncoordinated through the muscles of the atria causing them to quiver (sometimes more than 400 times per minute) without contracting. The ventricles do not receive regular impulses and contract out of rhythm, and the heartbeat becomes uncontrolled and irregular. It is the most common arrhythmia, and 85 percent of people who experience it are older than 65 years.

In Atrial Fibrillation, Rate will be 350 – 400 bpm, normal p waves absent or will be replaced by f waves

Medical Treatment
▪ Rate control
(slow ventricular rate to 80-100 beats/minute)
▪ Digoxin
▪ Beta-adrenergic blockers
▪ Calcium channel blockers
▪ Example – Verapamil (give IV if needed for quick rate control)
▪ Antithrombotic therapy
▪ Correction of rhythm
▪ Chemical or electrical cardioversion

Nursing Management

▪ Assess Patient
▪ O2 if not already given
▪ Start IV if not already established and hang NS
▪ Notify Medical Team
▪ Prepare for cardioversion

3. Supra Ventricular Tachycardia (SVT)

Encompasses all fast (tachy) dysrhythmias in which heart rate is greater than 150 beats per minute (bpm)

In supraventricular tachycardia, rate (atrial – 150 – 250 bpm, ventricular – 150 – 250 bpm) as well as p waves become hidden in QRS

Medical Treatment
▪ Stable patient’s (asymptomatic)
– Vagal maneuvers
▪ Drug management
– Adenosine
▪ Cardioversion if unstable

Nursing Management

▪ Assess Patient
▪ O2 if not already given
▪ Vagal maneuvers (cough and valsalva)
▪ Start IV if not already established and hang NS
▪ Notify MD
▪ Prepare for cardioversion

4. Premature Atrial Contraction

▪ A PAC is not a rhythm, it is an ectopic beat that originates from the atria.
▪ Normal beat, but just occurs early!!

Medical Treatment

▪ No treatment necessary if asymptomatic
▪ Treat the cause
▪ Drug therapy
▪ Beta Blockers
▪ Calcium Channel Blockers

5. Ventricular Tachycardia

Ventricular tachycardia almost always occurs in diseased hearts.
Rhythm in which three or more PVCs arise in sequence at a rate greater than 100 beats per minute.
V-tach can occur in short bursts lasting less than 30 seconds, causing few or no symptoms.
Sustained v-tach lasts for more than 30 seconds and requires immediate treatment to prevent death.

V-tach can quickly deteriorate into ventricular fibrillation.

QRS Complexes are usually wide and bizzare, rate is between 100 – 250 bpm

Medical Treatment
▪ If there is no pulse, begin CPR and follow ACLS protocol
▪ If there is a pulse and the patient is unstable – cardiovert and begin drug therapy
▪ Amiodarone
▪ Lidocaine
▪ With chronic or recurrent VT
▪ Give antiarrhythmics
▪ Long term may need ICD placed
▪ Ablation may be used for reentry

Nursing Management

– Assess your patient
– If symptomatic, treatment must be aggressive and immediate
– If Pulse present
• Oxygen
• Patent IV (preferably x2)
• Monitor patient very closely
– If patient is Pulseless
• Call Code Blue
• Begin CPR
• Defibrillate ASAP
• Start IV if not already established and hang NS
• Notify Medical team

6. Ventricular Fibrillation

– V-Fib (coarse and fine)
– Occurs as a result of multiple weak ectopic foci in the ventricles
– No coordinated atrial or ventricular contraction
– Electrical impulses initiated by multiple ventricular sites; impulses are not transmitted through normal conduction pathway

Medical treatment
▪ CPR with immediate defibrillation
▪ Initiate ACLS algorithm

Nursing Management
• Assess your patient
• Many things can mimic v-fib on a monitor strip such as electric razor or shivering
• You must check your patient!
• Treatment must be aggressive and immediate
• Start CPR/ACLS
• Call a Code Blue
• Defibrillate ASAP
• Start IV if not already established and hang NS
• Notify Medical Team

Myocardial Infarction and ECG

Anterior ST segment elevation MI

An anterior STEMI is usually from acute thrombotic occlusion of the left anterior descending coronary artery — also known as the “widow maker.”

This is named for obvious reasons. The J point is elevated and, along with the T wave, and it looks like a tombstone. In an anterior MI that shows “tombstoning,” there is frequently 4 to 6 millimeter of ST segment elevation. Do not confuse the ST segment elevation with the T wave. Look specifically where the ST segment is — waaaaay up from the baseline. Recall that the J point is where we need to measure the elevation from baseline, and the baseline is always the TP segment (between the T wave and the P wave).

Above one is another example of tombstoning with a slightly different shape. There is septal involvement (lead V2) and a bit laterally, as well (lead V5 and V6).

Inferior ST Segment Elevation MI

This MI involves ST segment elevation in the inferior leads II, III and aVF and only requires 1 mm in 2 contiguous leads. There is usually reciprocal depression in leads I and aVL, which helps to distinguish this from pericarditis.

Posterior ST Segment Elevation MI

The ECG criteria to diagnose a posterior MI — treated like a STEMI, even though no real ST segment elevation is apparent — include:

ST segment depression (not elevation) in V1 to V4. Think of things backwards. These are the septal and anterior ECG leads. The MI is posterior (opposite to these leads anatomically), so there is ST depression instead of elevation. Turn the ECG upside down, and it would look like a STEMI.
The ratio of the R wave to the S wave in leads V1 or V2 is greater than 1. This represents an upside-down Q wave (similar in reason to the ST depression instead of elevation).
ST segment elevation in the posterior leads of a posterior ECG (leads V7-V9). A posterior ECG is done by simply adding three extra precordial leads wrapping around the left chest wall toward the back.

Acute MI with a Right Bundle Branch Block

Hopes this article shows light towards understand functioning of Heart and interpreting ECG.

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