By: Devon Fuller EMT-P

P-WAVE AXIS AND ATRIAL ESCAPE RHYTHMS

INTRODUCTION• Proper interpretation of P-Wave axis

• P-Wave focus and morphology

• Ectopic beats involving P-Wave

• Escape rhythms and what to expect with treatment

P-WAVE• Technically defined as “a summation wave generated by the depolarization front as it

transits the atria”

• This translates to the first positive deflection on an ecg that represents atrial depolarization

• The P-Wave has criteria for being normal like the rest of the ECG

• Can be inverted, different shapes, tall, small, or even absent.

• The typical intrinsic rate represented by the depolarization of the P-Wave is 60-100 BPM

• If the P-Wave is present and the rate is below 60 BPM= Sinus Bradycardia

• If the P-Wave is present and the rate is above 100 BPM= Sinus Tachycardia

• If P-Wave is present, usually represents a normal sinus rhythm

P-WAVE RULES• Normal P-Wave morphology is as follows

Present

Upright

< 2.5 mm in limb leads and <1.5mm in precordial leads

Not wider than 120 ms

Remains same shape throughout 6 second strip

1 P-Wave preceding a QRS complex

Regular or Irregular

P-WAVE RULES CONT.• If all of the preceding rules are in effect, the P-Wave is indicated as “regular”

• P-Waves may be notched or biphasic and still represent a normal sinus rhythm

• Use the spacing between R-R intervals to indicate if the rhythm is regular or irregular

• Equal spacing between the R-R intervals indicates “regular”

• Any deviation from these rules indicate a possible ectopic beat

P-WAVE CONT.

• Present• Upright• < 2.5 mm tall• < 120 ms• Same shape (assume)• Preceding a QRS• Regularly-Regular (assume)

P-WAVE AXIS• Generally between 0 and +75

• Upright in leads I, II, and III

• Inverted in AVR

• Normal variant to be biphasic in V1 however not obvious

• If obviously biphasic in V1, a conduction issue is present

• First 1/3 of the P-Wave represents Right atrial contraction

• Last 1/3 of the P-Wave represent Left atrial contraction

• Middle 1/3 represents the signal across the Bachman Bundle (Intra-atrial bundle)

• If all are upright and symmetrical, the axis of the P-Wave is normal

• If byphasic or notched, the axis has shifted to the left or to the right

P-WAVE AXIS• P-Wave axis is 62 degrees, normal variant

P-WAVE AXIS CONT• Skewed axis is derived from primarily 3 determined conditions

• LAE- Left atrial enlargement

• RAE- Right atrial enlargement

• BAE- (No, not THAT bae)- Bi-atrial enlargement

RAE• In right atrial enlargement, right atrial depolarization lasts longer than normal and its

waveform extends to the end of left atrial depolarization.

• Although the amplitude of the right atrial depolarization current remains unchanged, its peak now falls on top of that of the left atrial depolarization wave.

• The combination of these two waveforms produces a P waves that is taller than normal (> 2.5 mm), although the width remains unchanged (< 120 ms).

LAE• In left atrial enlargement, left atrial depolarization lasts longer than normal but its

amplitude remains unchanged.

• The height of the resultant P wave remains within normal limits but its duration is longer than 120 ms.

• A notch (broken line) near its peak may or may not be present (“P mitrale”).

BI-ATRIAL ENLARGEMENT• Combination of both LAE and RAE

• First 1/3 of the P-Wave will be peaked

• Middle 1/3 may be notched or sloped but the conduction will be delayed

• Last 1/3 will be delayed >120 ms as it reaches the isoelectric line

• P-Wave will be biphasic in lead V1

OTHER P-WAVE ABNORMALITIES• Notched

• Biphasic

• Longer

• Shorter

• Taller

• Absent

• Inverted

• “Saw Tooth” – Flutter waves, AKA “F” waves

• Independent

P-WAVE IN ASSOCIATION TO RHYTHMS• Normal Sinus Rhythm

P-Wave normal, upright, preceding a QRS, same shape in 6 second strip, rhythm is “regularly-regular”

ECTOPIC ATRIAL RHYTHMS• Atrial Fibrillation

• Atrial Flutter

• Wandering Atrial Pacemaker

• Sinus Arrest

• Sinus Arrhythmia

• Sinus Exit Block

• Sick Sinus Syndrome

• Junctional Rhythm

ATRIAL FIBRILLATION• Atria are not in sync

• Too much either electrical interference, electrolyte imbalance, too many pacemaker sites, atrial hypoxia, trauma, congenital, etc..

• Can be extremely tachycardic as the signal from the atria is continuously sent to the ventricles

• Rule for A-Fib

P-Wave must be absent with notable electrical disturbances between the T wave and the following QRS complex

ATRIAL FIBRILLATION• Follow P-Wave Rules

• Present= No

• Upright= No

• Under 2.5 mm tall= No

• Not wider than 120 ms = No

• Same shape= No

• Preceding a QRS= No

• Irregularly-Irregular

ATRIAL FLUTTER• Atria are firing too fast but IN SYNC with electrical flow

• Caused conduction delay to the ventricles either by the Internodal Pathways, Bundle of His, AV-Node.

• Generally presents in a “Saw Tooth” pattern between QRS complexes but is technically called F-Waves

• Will generally follow the proper rules for P-Wave morphology although will have many P-Waves between QRS complexes.

ATRIAL FLUTTER• Present= Technically yes

• Upright= Yes

• Under 2.5 mm tall= Yes

• Not wider than 120 ms= Yes

• Same shape= Yes

• 1 wave preceding a QRS= NO

• Irregularly-Regular

• Conduction deficit may be documented in coordination with P-wave to QRS ratio, I.e. 3:1

WANDERING ATRIAL PACEMAKER• One of the rarest ectopic beats seen in the prehospital setting

• Patients generally know they have this condition and take medication for the same

• Often a precedes A-Fib in evolution of rhythm disturbances

• Different shapes of the P-Waves represent atrial depolarization, however from different pacemaker sites

• Rules

P-Waves present

Must have 3 P-Waves that are different shapes in a 6 second strip to be considered WAP

Still must precede a QRS complex

WANDERING ATRIAL PACEMAKER• Present= Yes

• Upright=Yes

• Under 2.5 mm tall= Possibly

• Not wider than 120 ms= Possibly

• Same Shape= NO

• Preceding a QRS= Yes

SINUS ARREST• Also known as Sinus Pause

• The electrical conduction from the Sinoatrial Node ceases temporarily

• If this ceases permanently, the patient goes into a Junctional rhythm

• Only 1 rule is technically defined for Sinus arrest/ Sinus pause

Must have at least 2 seconds between electrically conducted beats with no electrical conduction resulting on the ECG

• Often the rhythm will resume with normal P-QRS-T waves, but another pacemaker site may generate the electrical charge if the SA node does not resume conduction

• Most commonly found on patients who take beta-blockers and calcium channel blockers

SINUS ARREST• Present= Yes

• Upright= Yes

• Under 2.5mm Tall= Yes

• Not wider than 120 ms= Yes

• Same shape= Yes (depending)

• Preceding a QRS= Yes

• Regularly-Irregular

SINUS EXIT BLOCK• Result of the sinoatrial signal being blocked from continuing on its conduction vector

• Often confused with a sinus pause/ sinus arrest

• Difference will be between the P-P intervals

• Sinus arrest has NO P-Wave

• Sinus exit block will have a p-wave but will appear as a “bleb” between the ECG traced beats

• This “bleb” will only be represented by the first 1/3 of the P-Wave (right atrial conduction)

• The conduction delay may last longer than 2 seconds but other than a dropped QRS, the rhythm will remain regular

SINUS EXIT BLOCK• Present= Yes

• Upright= Yes

• Under 2.5 mm Tall= Yes

• Not wider than 120 ms= Yes

• Same Shape= Yes

• Preceding a QRS=Yes

• Regularly- Irregular

SINUS EXIT BLOCK VS. SINUS PAUSE

SINUS ARRHYTHMIA• EVERYONE HAS IT!!

• Considered benign by most means

• Defined as a normal increase in heart rate upon inspiration

• Not considered normal if at rest, the heart increases and decreases upon no general increase in inspiration or expiration

• General rules to follow are not set in stone, however one rule definitely remains

AT REST, a general increase AND decrease in heart rate in otherwise healthy adults may be defined as a malignant condition is other arrhythmias occur on an ECG tracing

SINUS ARRHYTMIA• Present= Yes

• Upright= Yes

• Under 2.5 mm Tall= Yes

• Not wider than 120 ms= Yes

• Same Shape= Yes

• Preceding a QRS= Yes

• Regularly- Irregular

SICK SINUS SYNDROME• Pretty easy to detect

• Technically defined as a group sinoatrial disorders

• May have two or ALL of the prior beats involved on an extended ECG tracing

• Tachy-brady disorder is often associated as the most common variant of SSS

• There are no real rules to follow in the pre-hospital setting for SSS

• You can be aware of a possibility if the patient notes to drop P-waves, become tachycardic, bradycardic, form a junctional rhythm, atrial flutter, back to normal sinus, and continue with a variation of ectopic rhythms

SICK SINUS SYNDROME• P-wave rules?

• Nope, not this time

• Only cardia condition to have a 3 name process: Regularly-irregularly-irregular

JUNCTIONAL RHYTHM• Absent or retrograde (inverted) P-Waves

• Intrinsic rate between 40-60 BPM

• Narrow QRS

• If above 60 BPM : Accelerated Junctional

• If below 40 BPM: Junctional Bradycardia

• If above 100 BPM: Junctional Tachycardia

JUNCTIONAL RHYTHM CONT• SA node fails to fire, will no longer fire, is hypoxic, or dead

• The Bundle of His or the AV node takes over

• You can tell where the conduction signal is originating from depending on the ECG tracing

If NO P-Wave is present, the origin is below the atria, typically from the Bundle of His

If a RETROGRADE P-Wave is present, the origin of conduction is coming from either the AV node or an additional pacemaker site at the Atria-ventricular junction, AKA ABOVE the ventricles

• In order for the rhythm to be considered Junctional, you must have absent or retrograde P-Waves present

• In some cases, the conduction vector will be just below the Bundle of His causing a delay in conduction backwards towards the Atria. This results in P-Waves in the ST segment

JUNCTIONAL RHYTHM• Present= N0

• Upright= Absent

• Under 2.5 MM tall= Absent

• Not wider than 120 ms= Absent

• Same shape= Absent

• Preceding a QRS= Absent

• Irregularly-regular

• Possible conduction origin?

JUNCTIONAL RHYTHM• Present= Yes

• Upright= No

• Under 2.5 mm tall= retrograde

• Not wider than 120 ms= yes

• Same shape= Yes

• Preceding a QRS=Yes

• Irregularly- regular

• Possible origin of conduction?

ST-SEGMENT P-WAVES• Conduction origin just below the Bundle of His

• Still results in a narrow QRS

• Delay from the BOH results in ST-Segment P-Waves

• ST-Segment P-Waves may be upright, inverted, biphasic, or notched

SUMMARY• Remember the rules for P-Wave determination and axis

• If the P-Wave is inverted, notched, or biphasic the axis is deviating away from the traditional conduction vector

• Make sure the P-Waves are as follows

• Present

• Upright

• Under 2.5 mm tall

• Not wider than 120 ms

• Same shape

• 1 preceding a QRS complex

REFERENCES• Skillstat.com

• Wikipedia

• Practicalclinicalskills.com

• AAOS Paramedic Tenth edition

• McGraw Hill “Paramedic”

• Clinical Cardiology: Current Practice Guidelines

• Cardiology Essentials

• http://lifeinthefastlane.com/ecg-library/basics/p-wave/