Module 3 ECG Rhythm Recognition

1. Module 3ECG Rhythm Recognition

2. 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)?

3. 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.

4. 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.

5. 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.

6. Muscle Tremor P P P P • 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.

7. 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.

8. Atrial extrasystoles (AE) x • 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.

9. x Atrial Fibrillation (AF) x x x x x • 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.

10. Atrial Flutter x x x • 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.

11. Supraventricular Tachycardia (SVT) x • 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.

12. Wolff-Parkinson-White Syndrome (WPW) Normal pathway Accessory pathway Paroxysmal tachycardia Delta wave PR anterograde / retrograde conduction • 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.

13. Junctional Rhythm (Nodal) x High Mid Low • 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.

14. First-degree Heart Block P P • 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.

15. Second-degree Heart Block Mobitz type I (Wenckebach) P R ? P P P P • 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.

16. 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.

17. 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.

18. Third-degree Heart Block (complete heart block) x x P P P P P P • 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.

19. Ventricular (Unifocal) Extrasystole x • 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.

20. Coupled Ventricular Extrasystole x • 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.

21. Couplets x • 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

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

23. Ventricular (Multifocal) Extrasystole x x x • 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.

24. Paced Beats x Pacing wire • A ventricular paced beat will display a broadened QRS complex. • The slim, deflection immediately preceding the R-wave denotes the pacing spike (arrowed above).

25. Idioventricular Rhythm x • 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.

26. 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.

27. Ventricular Tachycardia (VT) x • 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.

28. x Ventricular Fibrillation (VF) x x x x x x x x x • 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.

29. 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.

30. 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’ Haemothorax Toxicity Hypovolaemia Tension pneumothorax Hypo/hyperkalaemia Thrombo-embolic Hypothermia • 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.

31. 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.