EKG

The Cardiac Cycle

  • Definition: One complete cardiac cycle is defined as the sequence of P, Q, R, S, (QRS complex), and T wave.

Components of the Cardiac Cycle

  • P wave: Represents atrial depolarization (contraction).

  • QRS Complex: Represents ventricular depolarization, as well as atrial repolarization.

  • T wave: Represents ventricular repolarization (resting phase).

  • PR Interval: Time from the beginning of P wave to the beginning of QRS complex.

  • PR Segment: Time interval between the end of the P wave and the beginning of the QRS complex.

  • QT Interval: Time from the beginning of QRS complex to the end of the T wave.

Waveforms and Current Flow

  • Monitor Lead or ECG: Used to view electrical activity in the heart.

  • Direction: Indicates the flow and deflection of electrical impulses.

  • Deflection: Changes in the waveform as electrical activity spreads.

  • Magnitude: Size of the ECG waveforms, particularly the QRS complexes.

  • Biphasic Waves: ECG waves that show both positive and negative deflection.

ECG Graph Paper

  • PQRST Sequence: The arrangement of waves on the ECG tracing.

  • Horizontal Lines: Indicate time on the ECG graph.

  • Vertical Lines: Indicate amplitude or voltage on the ECG graph.

EKG Paper

  • Recording: ECG tracings are recorded on grid paper.

  • Time Measurement: The horizontal axis records time; marks indicate 3 second intervals.

    • Each second is denoted by 5 large grid blocks, therefore, each large block represents 0.2 seconds.

  • Voltage Measurement: The vertical axis registers amplitude (voltage).

    • Two large blocks equal 1 millivolt (mV); each small block represents 0.1 mV.

    • Each large block consists of 5 small blocks, with every small block representing 0.04 seconds.

Counting Heart Rate

  • Method: Fast & Dirty method.

  • Use: Suitable for both regular and irregular rhythms.

  • Accuracy: May become less accurate at very fast or slow rates.

  • Calculating Heart Rate:

    • Count the number of QRS complexes in 6 seconds; multiply by 10 to obtain beats per minute.

    • Example: If the above method shows a rate of 80 beats per minute.

Rhythm Strip Analysis Format

  • Factors for Analysis:

    • Regularity of Rhythm: Is it regular or irregular? Any pattern in irregularity?

    • Rate: What is the heart rate?

    • P Waves: Are there identifiable P waves?

    • PR Intervals: Measurement and consistency of PR intervals.

    • QRS Complexes: Characteristics of QRS complexes.

Step by Step Rhythm Interpretation

  • Determine Regularity: Identify if the rhythm is regular or irregular.

  • Calculate Rate: Determine if the rate is too slow or too fast.

  • Examine P Waves:

    • Is there a P wave for every QRS?

    • Is there a QRS for every P?

  • Measure PR Interval: Assess if the R to R interval is regular.

  • Evaluate QRS Duration: Determine if the QRS is wide or narrow.

Normal Sinus Rhythm

  • Origin: Arises from the SA node and follows appropriate conduction pathways.

  • Treatment: None required as it is normal.

  • Characteristics:

    • Rhythm: Regular

    • Rate: 60-100 bpm

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: 0.12 - 0.20 seconds

    • QRS Duration: 0.08 - 0.12 seconds (narrow).

Sinus Bradycardia

  • Origin: Arises in the SA node, characterized by a slower rate due to sympathetic input or excessive vagal tone.

  • Commonly Seen With: Inferior myocardial infarction (MI), hypoxia, hypothermia, or drug reactions.

  • Symptoms: Patient may be asymptomatic, but if symptomatic, treatment may include Atropine via IV, pacer pads, or external pacemaker.

  • Characteristics:

    • Rate: <60 bpm

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: 0.12 - 0.20 seconds

    • QRS Duration: 0.08 - 0.12 seconds (narrow).

Sinus Tachycardia

  • Origin: Arises in the SA node due to increased oxygen demand (e.g., exercise, infection, hypovolemia, hypoxia, MI, stimulant drugs).

  • Characteristics:

    • Rhythm: Regular/Fast

    • Rate: >100 bpm

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: 0.12 - 0.20 seconds

    • QRS: Normal.

Sinus Arrhythmia

  • Origin: Arises in the SA node, discharging impulses irregularly due to variations in autonomic tone associated with respirations without requiring treatment.

  • Characteristics:

    • Rhythm: Irregular

    • Rate: Normal 60-100 bpm or slow <60 bpm

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: 0.12 - 0.20 seconds

    • QRS Duration: 0.08 - 0.12 seconds.

Atrial Arrhythmias

Premature Atrial Contraction (PAC)

  • Characteristics:

    • Rhythm: Irregular with PACs

    • Rate: Dependent on the underlying rhythm.

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: 0.12 - 0.20 seconds

    • QRS Duration: 0.08 - 0.12 seconds (dependent on rhythm).

PSVT (Paroxysmal Supraventricular Tachycardia)

  • Characteristics:

    • Rhythm: Regular

    • Rate: 150-250 bpm

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: Dependent on the location of the circuit.

    • QRS Duration: 0.08 - 0.12 seconds or prolonged (greater than 0.12) with delta wave (Wolff-Parkinson-White syndrome).

Atrial Fibrillation

  • Characteristics:

    • Rhythm: Irregularly Irregular

    • Rate: Slow or fast

    • P waves: No identifiable P waves

    • PR Interval: Not measurable

    • QRS Duration: Normal (narrow) but may be wide with a conduction defect.

Atrial Flutter

  • Characteristics:

    • Rhythm: Can be regular or irregular, characterized by a “saw tooth” pattern in atrial activity.

    • Atrial rate: 250 to 400 bpm, Ventricular rate: Varies depending on the number of impulses conducted through the AV node.

    • P waves: Saw tooth wave deflection (F waves).

    • PR Interval: Not measurable

    • QRS Duration: Normal.

Atrioventricular Blocks

Overview of AV Blocks

  • Significance: Depends on the type, ventricular rate, and the patient’s response.

  • Dysrhythmias to Remember:

    • Bundle branch block

    • First-degree AV block

    • Second-degree AV Block, Type I (Mobitz I or Wenckebach)

    • Second-degree AV Block (Mobitz Type II)

    • Third-degree AV Block (complete heart block).

Definition of Atrioventricular Blocks

  • Heart block: A delay or failed conduction of supraventricular impulses through the AV node into the ventricles.

  • Location of Problem: May be located in the AV junction, bundle of HIS, or bundle branches.

  • Key Diagnostic Tool: The PR interval is essential to determine the degree of block.

  • QRS Width: Determines the block's location; wider QRS indicates lower blocks.

  • Significance Factors: Type of block, ventricular rate, and the response of the client.

Bundle Branch Block (BBB)

  • Characteristics:

    • Rhythm: Usually regular

    • Rate: The underlying rhythm

    • P wave: Sinus

    • PR Interval: Normal (0.12-0.20 seconds)

    • QRS Duration: Wide (>0.12 seconds).

First Degree AV Block

  • Characteristics:

    • Rhythm: Regular

    • Rate: The underlying rhythm

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: Prolonged (>0.20 seconds)

    • QRS Duration: Normal (<0.12 seconds).

Second Degree AV Block, Type I (Mobitz I or Wenckebach)

  • Characteristics:

    • Rhythm: Regular atrial, irregular ventricular.

    • Rate: Atrial follows underlying rhythm; Ventricular rate depends on impulses received.

    • Every P wave has a QRS, and every QRS has a P wave.

    • PR Interval: Prolonged (>0.20 seconds) until a dropped beat occurs (pattern: long, longer, drop).

    • QRS Duration: <0.12 seconds.

Second Degree AV Block, Type II (Mobitz Type II)

  • Characteristics:

    • Rhythm: Atrial regular, ventricular usually regular but may be irregular.

    • Rate: Atrial follows underlying rhythm; Ventricular depends on number of impulses.

    • Pattern: 2 or 3 P waves (sometimes more) may come before each QRS complex.

    • PR Interval: May be normal or prolonged, remains constant.

    • QRS Duration: Normal if block occurs at the AV node or bundle of His; wide if block occurs in bundle branches.

Third Degree AV Block (Complete Heart Block)

  • Characteristics:

    • Rhythm: Regular (both ventricular and atrial but at different rates).

    • Rates: Atrial: 60 to 100 bpm; Ventricular: 40 to 60 bpm.

    • PR Interval: Varies with no discernible pattern.

    • QRS Duration: Depends on the origin of the impulse:

    • From the AV node: QRS will be normal.

    • From the Purkinje system: QRS will be wide, with a rate <40 bpm.

Ventricular Arrhythmias

Overview of Ventricular Arrhythmias

  • Characteristics:

    • Electrical impulses bypass normal conduction pathways.

    • Alteration in electrophysiology mechanism.

  • Dysrhythmias to Remember:

    • Premature Ventricular Contractions (PVCs)

    • Ventricular Tachycardia

    • Ventricular Fibrillation (V-Fib)

    • Ventricular Standstill or Asystole

    • Pulseless Electrical Activity (PEA).

Premature Ventricular Contractions (PVCs)

  • Characteristics:

    • Rhythm: Underlying rhythm is regular; becomes irregular with PVC.

    • Rate: Underlying rhythm.

    • P wave: Usually absent.

    • PR Interval: Not measurable.

    • QRS Duration: >0.12 seconds; premature and “wide and bizarre.”

Ventricular Tachycardia (V-Tach)

  • Characteristics:

    • Rhythm: May be irregular, but usually regular.

    • Rate: Typically regular, ranges from 140 - 250 bpm.

    • P wave: May be absent, inverted, or retrograde.

    • PR Interval: Not measurable.

    • QRS Duration: Complexes appear bizarre, >0.12 seconds.

Ventricular Fibrillation (V-Fib)

  • Characteristics:

    • Rhythm: Irregular-coarse or fine; waveform varies in size and shape leading to chaotic activity.

    • Rate: 0 (no P waves or QRS complexes present).

    • P waves: Absent; appear as wavy, irregular patterns varying in size, height, and shape.

    • PR Interval: Not measurable.

    • QRS: Absent; no discernible complexes.

Ventricular Standstill or Asystole

  • Characteristics:

    • Definition: No electrical activity.

    • Rate: Absent due to lack of ventricular activity.

    • Occasionally, a P wave may be identified.

    • Patient Condition: No pulse is present.

Pulseless Electrical Activity (PEA)

  • Characteristics:

    • Rhythm: Evidence of organized electrical activity without a pulse.

    • Rate: Shows electrical activity but no muscle contraction (no pulse).

    • PR Interval: May appear normal.

    • QRS: Varies; any rhythm can be seen on the monitor, but no contraction occurs.