Module 3ECG Rhythm Recognition

What to Look for on a rhythm strip

• Are all the P waves alike?• Are all the QRS complexes alike?• Are all the P waves and QRS complexes related or

occurring independently?• Is there a P wave in front of every QRS complex?• Is the PR interval constant or does it vary?• Is the PR interval too short (<0.12 s) or too long (>0.2 s)?• Is the QRS complex widened (>0.12 s)?

Normal Sinus Rhythm

• NSR is a rate of between 60-100bpm.• Each beat normally has one P wave, one corresponding QRS

complex and T wave.• The R-R intervals should be regular and constant.• The P-R interval is within normal range.

Sinus Bradycardia

• R-R intervals constant and regular.• All waveforms are present, and there is 1 P-wave to each QRS

complex.• The rate is <60bpm but not usually <40bpm.• Patients usually asymptomatic and no treatment is required.• Often caused by beta-blockers/calcium channel blockers.• May also be seen in athletes and occur during sleep.

Sinus Tachycardia

• R-R intervals constant and regular.• One P-wave per QRS complex.• All waveforms present.• Rate is >100bpm, but not usually >130bpm at rest.• Occurs normally in exercise/stress. Patient is usually asymptomatic.• Other causes may be hypovolaemia/underlying medical problems.

Muscle Tremor

• All waveforms are present, but are difficult to define due to the wavering appearance on the isoelectric line.

• Common causes of muscle tremor are patient shivering or anxiety.

• It may be difficult to accurately assess an ECG where muscle tremor is present.

P P P P

Electrical Interference

• It may be difficult to make any assessment of an ECG where there is electrical interference; none of the waveforms are clearly defined.

• Common causes of this phenomenon are any electrical appliances in close proximity to the ECG machine: i.e TV, electrical beds, infusion pumps etc.

• Usually once all appliances are unplugged, a satisfactory quality ECG can be carried out.

Atrial extrasystoles (AE)

• AE’s are a common form of supraventricular extrasystole.• Cause is atrial beat arising outside the sinus node.• Patients are generally asymptomatic and there is no treatment

indicated.• A trial extrasystole falling on a critical time of atrial repolarisation

may trigger atrial fibrillation (AF) in some vulnerable patients.

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Atrial Fibrillation (AF)

• The atrial depolarisation is disorganised resulting in a chaotic ventricular rhythm.

• The ventricular response rate may be normal/fast/slow.• This is a common arrhythmia, especially in the elderly; around

5-10% of whom experience AF. • Treatment is usually with oral drug therapy, although may be

successfully electrically cardioverted in patients with persisting AF of recent onset.

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Atrial Flutter

• A malfunction in the pattern of atrial depolarisation. A flutter usually gives atrial waves in the range of 280-320bpm.

• The AV node usually blocks 1/2 of these impulses and gives a ventricular response rate of 150bpm.

• Atrial flutter is usually regular in rhythm and displays a ‘saw-toothed’ appearance (especially V1) as above.

• Very responsive to DC electrical cardioversion.

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Supraventricular Tachycardia (SVT)

• SVT is a general term for tachycardias that originate above the ventricles.

• Rate may be in the range of - 150-250bpm • Commonly starts in early adult life and is normally inconvenient

but benign. • Vagal manouevres should be used initially. Adenosine and/or

cardioversion used in hospital.

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Wolff-Parkinson-White Syndrome (WPW)

• WPW is a syndrome with a characteristic electrocardiogram - shortened PR interval (<0.12secs) and a slurred upstroke on the QRS complex (delta wave) together with a tendency to supraventricular arrhythmias.

• It is caused by an accessory conduction pathway which bypasses the AV node.

Accessory pathway

Delta wave

PR

Normal pathway

anterograde / retrograde conduction

Paroxysmal tachycardia

Junctional Rhythm (Nodal)

• When the electrical pathway originates further down in the conduction system, but is still coming from or near the AV node, a ‘nodal’ (junctional) rhythm occurs.

• If the pacemaker is high - an inverted P-wave may occur before the QRS complext.

• If the pacemaker is within the node - the P-wave is usually absent.• If the conducting pathway is lower down, then the P-wave may have an

inverted appearance and occur after the QRS and even resemble a S wave.

x High Mid Low

First-degree Heart Block

• The measurement from the start of the P-wave to the start of the R-wave is prolonged to >5 sm squares (0.20secs).

• The P-waves and R-waves remain constant and regular.• The heart rate is usually within normal parameters.• Patient is not compromised and no treatment indicated.• Caused by delay within the AV node.

P P

Second-degree Heart Block Mobitz type I (Wenckebach)

• The P-R interval becomes progressively elongated with each heart beat; eventually conduction fails completely.

• The cycle then repeats itself once again.• May be seen in individuals with high vagal tone especial during

sleep.• Where it occurs in complication of inferior MI, it does not usually

require a pacemaker and often may be reversed with myocardial reperfusion.

?P R

P P P P

Second-degree Heart Block Mobitz type II

• Most P-waves conducted as normal - followed by QRS.• The P-R interval is normal and usually constant.• Occasionally, the atrial conduction is not followed by a QRS

complex.• Thought to be caused by an abnormality in the bundle of His.• Considered more serious than type I block in that it can

progress to complete heart block without warning.

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2:1 Heart Block

• Every alternate P-wave is not conducted.• Cannot be classified as either Mobitz Type I or Mobitz Type II.• Use of a pacemaker may be considered.

Third-degree Heart Block (complete heart block)

• The P-P and R-R intervals are each usually regular but have no relation to each other.

• This dissociation is due to a block at the AV junction.

x x P P P P P P

Ventricular (Unifocal) Extrasystole

• Occasional extrasystoles are common in healthy adults.• 3 or more in a row may be described as VT, but shorter runs are

usually called salvoes. • The morphology of each ectopic is unchanged if depolarisation

originates from a single focus.

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Coupled Ventricular Extrasystole

• This is the term used when every alternate beat is an extrasystole.

• Treated only in exceptional circumstances.• Coupled extrasystole may cause bigeminy: the condition in

which alternate ectopic beats of the heart are transmitted to the pulse and felt as a double pulse beat followed by a pause.

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Couplets

• A couplet is where there are 2 ventricular ectopics in a row.• Not usually treated except in circumstances that make the

patient vulnerable to more serious arrhythmias

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R on T Extrasystole

• When the ventricular extrasystole falls on the T-wave. This may trigger serious ventricular arrhythmias.

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• Where the origin of the ectopic beat originates from differing foci within the ventricle.

• This may signify a high degree of ventricular excitability.• Although extrasystoles may occasionally precipitate more

malignant arrhythmias, any decision on treatment should be made only after considering the risk of anti-arrhythmic drugs.

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Ventricular (Multifocal) Extrasystole

Paced Beats

• A ventricular paced beat will display a broadened QRS complex.

• The slim, deflection immediately preceding the R-wave denotes the pacing spike (arrowed above).

xPacing wire

Idioventricular Rhythm

• Often seen with reperfusion following acute MI, idioventricular rhythm can be regarded as ‘slow VT’.

• The QRS is broad and bizarre, but uniform and regular. • The rate is less than 100bpm.• Usually no treatment is indicated.

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Torsades de Pointes

• From the French ‘twisting of points’. This describes a form of VT where the cardiac axis twists round the isoelectric line.

• The rhythm may be intermittent and self-terminating. If it lasts more than a few seconds the patient will become symptomatic.

• Common causes are electrical imbalance - i.e K+ and/or Mg++ depletion or prolonged Q-T interval frequently caused by drugs such as Sotalol/Amiodarone or tricyclic antidepressants.

• The origin of the heartbeat is in the ventricles, producing a QRS complex >0.12secs.

• 3 ventricular beats in succession may be called VT (or salvoes).• VT can range in rate from 100-300bpm and the patient may be

conscious and asymptomatic, symptomatic, or unconscious. Treatment will depend principally on the patients’ clinical status.

Ventricular Tachycardia (VT)

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Ventricular Fibrillation (VF)

• The ventricles are ‘quivering’, leading to a complete loss of cardiac output.• Bizarre complexes are characteristic, but are variable amplitude (course /

fine VF).• The most common arrhythmia causing cardiac arrest, but becomes finer

as minutes pass and soon becomes indistinguishable with asystole.• Patient will require immediate defibrillation (10% reduction in success rate

as each minute passes).• Most common cause of death in early acute MI.

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Ventricular Standstill

• No ventricular response to atrial depolarisation.• There is no cardiac output and the patient is in cardiac arrest.• Pacing is required. It is usually effective if atrial activity is

present.

Pulseless Electrical Activity (PEA)

•PEA describes a condition where QRS complexes continue but no cardiac output can be detected.•8 treatable causes: ‘4 Ts’ Tamponade ‘4 Hs’ HaemothoraxToxicity Hypovolaemia Tension pneumothorax Hypo/hyperkalaemia Thrombo-embolicHypothermia•No cardiac output, although the rhythm displayed may be that of a non

life threatening nature.•Treatment is life support as per non-VT/VF protocol until a cause is established.

Asystole

• Implies the absence of ventricular activity.• No QRS complexes are present.• Patient is in a state of full cardiac arrest.• In asystole - always check patient, check leads, check

monitoring mode (? Paddles), increase the monitoring gain to rule out fine VF.