- ADVANCED ECG INTERPRETATION -

Question 1

Discuss the phases of the action potential of myocardial cells

Answer 1

Phase 0 - Rapid depolarisation (influx of Na+) Phase 1 - Partial repolarisation (deactivation of Na+ influx and eflux of K+) Phase 2 - Plateau (slow influx of Ca2+, equals the efflux of K+) Phase 3 - Repolarisation (deactivation of Ca2+ influx, K+ eflux) Phase 4 - Pacemaker potential (slow influx of Na+ which slows the eflux of K+, “autorhythmicity”) Refractory period - Phases 1-3

Question 2

Discuss the sodium cycle in the myocardial cells

Answer 2

-.The sodium pump is responsible for the initiation of the action potential - It is voltage dependant and thus sodium moves rapidly - These channels are open during phase 0, allowing for the rapid influx of sodium ions - This influx causes an increase in the membrane potential4 - As the membrane potential increases the sodium channels close again - During this inactivation state sodium cannot pass through the membrane ( this is relevant for the absolute refractory period phases 1-3)

Question 3

Discuss the calcium cycle in myocardium cells

Answer 3

.- There is an influx of Calcium in phase 2 which is steady and equals the potassium out, resulting in a plateau - the influx of calcium is largely responsible for contraction of the muscle - there are 2 types of calcium channels T and L type channels - T channels act faster and contribute to depolarisation, phase 0, and L channels are active in phase 2, plateau phase, and allow for a slow influx of calcium

Question 4

Discuss depolarisation, repolarisation and resting membrane potential of myocardial cells

Answer 4

.Depolarisation - phase 0 (action potential triggered by neighbouring cells through gap junctions, raises transmembrane potential, Fast Na+ channels open and rapid influx of sodium, increasing the voltage of the cell Repolarisation - Early repolarisation in phase 1 as som potassium leaks out of the cell, full repolarisation in phase 3 as the calcium channels are closed and potassium continues to leak out bringing the voltage back down to -90mv

Question 5

Discuss the absolute, effective and relative refractory periods of myocardial cells as well as supra

Answer 5

.Absolute refractory period (ARP): the cell is completely unexcitable to a new stimulus. Phase 2. Effective refractory period (ERP): ARP + short segment of phase 3 during which a stimulus may cause the cell to depolarize minimally but will not result in a propagated action potential (i.e. neighbouring cells will not depolarize). Relative refractory period (RRP): a greater than normal stimulus will depolarize the cell and cause an action potential. Phase 3. Supranormal period: a hyperexcitable period during which a weaker than normal stimulus will depolarize the cells and cause an action potential. Cells in this phase are particularly susceptible to arrhythmias when exposed to an inappropriately timed stimulus, which is why one must synchronize the electrical stimulus during cardioversion to prevent inducing ventricular fibrillation.

Question 6

Define axis deviation

Answer 6

The electric axis of the heart is the net direction in which the wave of depolarisation travels.

Question 7

Discuss how to identify left and right axis deviation

Answer 7

RAD: Lead I - negative avF/III - positive LAD: Lead I - positive avF/III - negative

Question 8

Discuss the causes of left/right axis deviation

Answer 8

Right axis deviation (RAD): Right ventricular hypertrophy Acute right ventricular strain, e.g. due to pulmonary embolism Lateral STEMI Chronic lung disease, e.g. COPD Hyperkalaemia Sodium-channel blockade, e.g. TCA poisoning Wolff-Parkinson-White syndrome Dextrocardia Ventricular ectopy Secundum ASD – rSR’ pattern Normal paediatric ECG Left posterior fascicular block – diagnosis of exclusion Vertically orientated heart – tall, thin patient Left Axis Deviation (LAD): Left ventricular hypertrophy Left bundle branch block Inferior MI Ventricular pacing /ectopy Wolff-Parkinson-White Syndrome Left anterior fascicular block – diagnosis of exclusion Horizontally orientated heart – short, squat patient Extreme axis deviation: Ventricular rhythms – e.g.VT, AIVR, ventricular ectopy Hyperkalaemia Severe right ventricular hypertrophy

Question 9

Outline the criteria to identify ST elevation (and lead groupings)

Answer 9

.o ≥2 mm of ST segment elevation in 2 contiguous precordial leads in men (1.5 mm for women) o ≥1mm in other leads (2 contiguous) o An initial Q wave or abnormal R wave develops over a period of several hours to days.

Question 10

Outline the ECG lead groupings

Answer 10

Inferior - Lead II, III, and avF Lateral - Lead I, avL, V5, V6 Anterior - V3, V4 Septal - V1, V2

Question 11

Outline the criteria to identify 1st degree block

Answer 11

• PR interval > 200ms (five small squares) - ‘Marked’ first degree block if PR interval > 300ms - P waves buried in preceding T waves

Question 12

Outline the criteria to identify 2nd degree block (Mobitz I) (Wenckebach)

Answer 12

• Progressive prolongation of the PR interval culminating in a non-conducted P wave - The PR interval is longest immediately before the dropped beat - The PR interval is shortest immediately after the dropped beat

Question 13

Outline the criteria to identify 3rd degree block ( complete heart block)

Answer 13

• atrial and ventricular pacing is regular but completely unrelated to one another - two seperate, regular rates - .None of the atrial impulses appear to be conducted to the ventricles. - Rhythm is maintained by a junctional escape rhythm.

Question 14

Outline the criteria to identify supraventricular tachycardia

Answer 14

• P waves are often hidden – being embedded in the QRS complexes. - Pseudo R’ wave may be seen in V1 or V2. - Pseudo S waves may be seen in leads II, III or aVF. - In most cases this results in a ‘typical’ SVT appearance with absent P waves and tachycardia

Question 15

Outline the criteria to identify left bundle branch block

Answer 15

• QRS duration of > 120 ms - Dominant S wave in V1 - Broad monophasic R wave in lateral leads (I, aVL, V5-V6) - Absence of Q waves in lateral leads (I, - V5-V6; small Q waves are still allowed in aVL) - Prolonged R wave peak time > 60ms in left precordial leads (V5-6) - Appropriate discordance: the ST segments and T waves always go in the opposite direction to the main vector of the QRS complex - Poor R wave progression in the chest leads - Left axis deviation

Question 16

Outline the criteria to identify right bundle branch block

Answer 16

• Broad QRS > 120 ms - RSR’ pattern in V1-3 (‘M-shaped’ QRS complex) - Wide, slurred S wave in the lateral leads (I, aVL, V5-6)

Question 17

Outline the criteria to identify left anterior fascicular block (LAFB)

Answer 17

• Left axis deviation (usually between -45 and -90 degrees) - Small Q waves with tall R waves (= ‘qR complexes’) in leads I and aVL - Small R waves with deep S waves (= ‘rS complexes’) in leads II, III, aVF - QRS duration normal or slightly prolonged (80-110 ms) - Prolonged R wave peak time in aVL > 45 ms - Increased QRS voltage in the limb leads

Question 18

Outline the criteria to identify left posterior fascicular block (LPFB)

Answer 18

• Right axis deviation (> +90 degrees) - Small R waves with deep S waves (= ‘rS complexes’) in leads I and aVL - Small Q waves with tall R waves (= ‘qR complexes’) in leads II, III and aVF - QRS duration normal or slightly prolonged (80-110ms) - Prolonged R wave peak time in aVF - Increased QRS voltage in the limb leads - No evidence of right ventricular hypertrophy - No evidence of any other cause for right axis deviation

Question 19

Outline the criteria to identify a bifascicular block

Answer 19

• Bifascicular block is the combination of RBBB with either LAFB or LPFB. - Conduction to the ventricles is via the single remaining fascicle. - The ECG will show typical features of RBBB plus either left or right axis deviation. - RBBB + LAFB is the most common of the two patterns.

Question 20

Outline the criteria to identify a trifascicular block

Answer 20

.Trifascicular block (TFB) refers to the presence of conducting disease in all three fascicles: - Right bundle branch (RBB) - Left anterior fascicle (LAF) - Left posterior fascicle (LPF) The most common is a combination of bifascicular block with 1st degree AV block. Incomplete trifascicular block: - Bifascicular block + 1st degree AV block (most common) - Bifascicular block + 2nd degree AV block - RBBB + alternating LAFB / LPFB Complete trifascicular block: - Bifascicular block + 3rd degree AV block

Question 21

Outline the criteria to identify wolf parkinson white

Answer 21

• Wolff-Parkinson-White (WPW) Syndrome is a combination of the presence of a congenital accessory pathway and episodes of tachyarrhythmia - PR interval <120ms - Delta wave – slurring slow rise of initial portion of the QRS - QRS prolongation >110ms - ST Segment and T wave discordant changes – i.e. in the opposite direction to the major component of the QRS complex

Question 22

Outline the criteria to identify an accelerated idioventricular rhythm

Answer 22

• Regular rhythm. - Rate 50-110 bpm. - Three or more ventricular complexes. - QRS complexes >120ms. - Fusion and capture beats.

Question 23

Outline the criteria to identify accelerated junctional rhythm

Answer 23

• Narrow complex rhythm; QRS duration < 120ms (unless pre-existing bundle branch block or rate-related aberrant conduction). 0
• Ventricular rate usually 60 – 100 bpm.
• Retrograde P waves may be present and can appear before, during or after the QRS complex.
• Retrograde P waves are usually inverted in the inferior leads (II, III, aVF), upright in aVR + V1.
• AV dissociation may be present with the ventricular rate usually greater than the atrial rate.
• There may be associated ECG features of digoxin effect or digoxin toxicity.

Question 24

Outline the criteria to identify dilated cardiomyopathy

Answer 24

. - The most common ECG abnormalities are those associated with atrial and ventricular hypertrophy — typically, left sided changes are seen but there may be signs of biatrial or biventricular hypertrophy. - Interventricular conduction delays (eg. LBBB) occur due to cardiac dilatation.

Question 25

Outline the criteria to identify hyperkalaemia

Answer 25

.Peaked t wave - t wave can be bigger than QRS in lead II

Question 26

Describe the mechanism of arrythmia formation

Answer 26

.Arrythmias are usually due to: - Impaired automaticity: problems with impulse formation - Abnormal impulse conduction – conduction block or reentry - Triggered activity

Question 27

Compare the ECG characteristics of a left and a right bundle branch block

Answer 27

1. LBBB: monophasic, negative QRS in V1 RBBB: biphasic QRS 'RSR' in lead V1 2. In an RBBB, the S-wave is slurred while in an LBBB there are broad R-waves with the absence of Q-waves. 3. Both should have more than 0.12 seconds of QRS waves.

Question 28

Outline the significance of a left bundle branch block in an acute MI

Answer 28

- In patients with left bundle branch block (LBBB) or ventricular paced rhythm, the baseline ST segments and T waves tend to be shifted in a discordant direction (“appropriate discordance”), which can mask or mimic acute myocardial infarction. - A new LBBB is always pathological and can be a sign of myocardial infarction. - Use of the Sgarbossa criteria is used for diagnostic accuracy: - ≥ 1 lead with ≥1 mm of concordant ST elevation - ≥ 1 lead of V1-V3 with ≥ 1 mm of concordant ST depression - ≥ 1 lead anywhere with ≥ 1 mm STE and proportionally excessive discordant STE, as defined by ≥ 25% of the depth of the preceding S-wave.

Question 29

Explain the ECG criteria pertaining to hemiblocks

Answer 29

left anterior hemiblock: - QRS axis more left than -30 degrees - initial R wave in the inferior leads (II, III and aVF) - absence of any other cause of left axis deviation

Question 30

Outline the significance and nursing management of 1st degree heart block

Answer 30

1st degree block: - Does not cause haemodynamic disturbance - No specific treatment is required

Question 31

Discuss the characteristics, description, and significance of ST elevation

Answer 31

CRITERIA FOR A STEMI: .o ≥2 mm of ST segment elevation in 2 contiguous precordial leads in men (1.5 mm for women) o ≥1mm in other leads (2 contiguous) o An initial Q wave or abnormal R wave develops over a period of several hours to days.

Question 32

Discuss the characteristics, description, and significance of pathological Q waves from a non-pathological Q waves

Answer 32

Q waves are considered pathological if: - \> 40 ms (1 mm) wide - \> 2 mm deep - \> 25% of depth of QRS complex - Seen in leads V1-3 Pathological Q waves usually indicate current or prior myocardial infarction.

Question 33

Discuss the characteristics, description, and significance of abnormal QRS complexes

Answer 33

1. Width of the complexes: - think: LBBB, RBBB, hyperkalaemia, tricyclic poisoning, WPW, ventricular pacing, hypothermia 2. Narrow versus broad. Voltage (height) of the complexes: - think: left ventricular hypertrophy, massive pericardial effusion, slim/athletic build \*\*\*\*\*\*\*\*note\*\*\*\*\*\* Sokolov-Lyon criteria (S wave depth in V1 + tallest R wave height in V5-V6 \> 35 mm).

Question 34

Discuss the characteristics, description, and significance of abnormal P waves (including ectopic P waves)

Answer 34

- P mitrale (bifid P waves), seen with left atrial enlargement. - P pulmonale (peaked P waves), seen with right atrial enlargement. - P wave inversion, seen with ectopic atrial and junctional rhythms. - Variable P wave morphology, seen in multifocal atrial rhythms.

Question 35

Discuss the characteristics, description, and significance of abnormal T waves (including R wave progression)

Answer 35

- Hyperacute T waves (STEMI, Prinzmetal angina) - Inverted T waves (normal in paeds, MI, BBB, PE, hypertrophy, raised ICP) - Biphasic T waves (ischaemia, hypokalaemia) - ‘Camel Hump’ T waves (prominant u waves - hypokalaemia, or hidden p waves - heart blocks) - Flattened T waves (ischaemia, hypokalaemia)

Question 36

Discuss the characteristics, description, and significance of premature atrial contraction

Answer 36

PACs - An abnormal (non-sinus) P wave is followed by a QRS complex (unifocal - abnormal p waves the same in morphology, multifocal - varying morphologies) \*\*\*\*bigeminy, trigeminy, quadrigeminy, couplet, triplet - not usually requiring investigation or treatment but may be the trigger for the onset of a re-entrant tachydysrhythmia

Question 37

Identify the mechanism, characteristics and nursing management of the narrow complex tachycardia, sinus tachycardia

Answer 37

. - Can be AV node independent (ST, AT, AF, AFlutter), or AV node dependent (AVNRT, AVRT, juctional tachycardia) - Treatment is different for each type of narrow complex tachycardia: - vagal manoeuvre adenosine 6-12mg IV (half dose if cardiac transplant or on dipryidamole) -\> AV node independent: decreased AV node conduction but tachycardia persists -\> AV node dependent: arrhythmia ceases

Question 38

Identify the mechanism, characteristics and nursing management of the narrow complex tachycardia, atrial flutter with a 2:1 block

Answer 38

Characteristics: - Narrow complex tachycardia at 150 bpm (range 130-170; with 2:1 AV block) - Turn the ECG upside down and scrutinise the inferior leads (II, III + aVF) for flutter waves Management: - Vagal Manoeuvres +/- Adenosine (Atrial flutter will not usually cardiovert with these techniques (unlike AVNRT), although typically there will be a transient period of increased AV block during which flutter waves may be unmasked)

Question 39

Identify the mechanism, characteristics and nursing management of the narrow complex tachycardia, AV nodal re-entry tachycardia

Answer 39

- .vagal manoeuvres - adenosine - verapamil - sotalol - amiodarone - flecanide - overdrive pacing - cardioversion

Question 40

Identify the mechanism, characteristics and nursing management of the narrow complex tachycardia, accessory pathway AV re-entry tachycardia

Answer 40

. - vagal manoeuvres - adenosine - sotalol - amiodarone - flecanide - overdrive pacing - cardioversion -\> same as AVNRT Tx EXCEPT avoidance of verapamil as leads to rapid conduction down accessory pathway (WPW).

Question 41

Identify the predisposing factors, mechanism, characteristics and management of monomorphic VT

Answer 41

- Ventricular tachycardia may impair cardiac output with consequent hypotension, collapse, and acute cardiac failure. This is due to extreme heart rates and lack of coordinated atrial contraction (loss of “atrial kick”) - The presence of pre-existing poor ventricular function is strongly associated with cardiovascular compromise. - Decreased cardiac output may result in decreased myocardial perfusion with degeneration to VF - Prompt recognition and initiation of treatment (e.g. electrical cardioversion) is required in all cases of VT Classified based on morphology, is it SUSTAINED? (\>30sec), is it STABLE? (haemodynamically)

Question 42

Identify the predisposing factors, mechanism, characteristics and management of polymorphic VT and Torsade de point

Answer 42

- TdP is often short lived and self terminating, however can be associated with hemodynamic instability and collapse. TdP may also degenerate into ventricular fibrillation (VF) - Can occur secondary to drug effects, electrolyte abnormalities, and medical conditions - Management strategies revolve around treating the cause (magnesium, isoprenaline, overdrive pacing, etc)

Question 43

Identify the ECG characteristics indicative of electrolyte imbalances

Answer 43

Hypokalaemia - Long QU interval, prominant U waves Hyperkalaemia - peaked T-waves Hypocalcaemia - prolonged QT Hypercalcaemia - shortening of ST segment

Question 44

Discuss the significance of a prolonged QT interval

Answer 44

The QT interval should be measured in either lead II or V5-6 and be greater than........ Causes: - Hypokalaemia - Hypomagnesaemia - Hypocalcaemia - Hypothermia - Myocardial ischemia - Post-cardiac arrest - Raised intracranial pressure - Congenital long QT syndrome - DRUGS \*\*\*Increased risk of ventricular arrythmias esp. torsades de pointes

Question 45

Discuss the potassium cycle in myocardial cells

Answer 45

- Two types of potassium channels (inward rectifiers and voltage-gated potassium channels) - inward rectifiers allow potassium inward during phase 4 to be in normal state - voltage-gated channels allow for the efflux of potassium through phases 1-3

Question 46

Outline the criteria for ST depression

Answer 46

- ST depression can be either upsloping, downsloping, or horizontal (see diagram below). - Horizontal or downsloping ST depression ≥ 0.5 mm at the J-point in ≥ 2 contiguous leads indicates myocardial ischaemia (according to the 2007 Task Force Criteria). - ST depression ≥ 1 mm is more specific and conveys a worse prognosis. - ST depression ≥ 2 mm in ≥ 3 leads is associated with a high probability of NSTEMI and predicts significant mortality (35% mortality at 30 days). - Upsloping ST depression is non-specific for myocardial ischaemia.

Question 47

Outline the criteria to identify 2nd degree block (Mobitz II)

Answer 47

- Intermittent non-conducted P waves without progressive prolongation of the PR interval (compare this to Mobitz I). - The PR interval in the conducted beats remains constant. - The P waves ‘march through’ at a constant rate. - The RR interval surrounding the dropped beat(s) is an exact multiple of the preceding RR interval (e.g. double the preceding RR interval for a single dropped beat, treble for two dropped beats, etc).

Question 48

Outline the significance and nursing management of 2nd degree block (Mobitz I/wenckebach):

Answer 48

- usually a benign rhythm, causing minimal haemodynamic disturbance and with low risk of progression to third degree heart block. - Asymptomatic patients do not require treatment. Symptomatic patients usually respond to atropine. Permanent pacing is rarely required.

Question 49

Outline the significance and nursing management of 2nd degree block (Mobitz II)

Answer 49

- Mobitz II is much more likely than Mobitz I to be associated with haemodynamic compromise, severe bradycardia and progression to 3rd degree heart block. - Onset of haemodynamic instability may be sudden and unexpected, causing syncope (Stokes-Adams attacks) or sudden cardiac death. - The risk of asystole is around 35% per year. - Mobitz II mandates immediate admission for cardiac monitoring, backup temporary pacing and ultimately insertion of a permanent pacemaker.

Question 50

Outline the significance and nursing management of 3rd degree heart block (CHB)

Answer 50

- Patients with third degree heart block are at high risk of ventricular standstill and sudden cardiac death. - They require urgent admission for cardiac monitoring, backup temporary pacing and usually insertion of a permanent pacemaker.

Question 51

Discuss the characteristics, description, and significance of premature ventricular contraction

Answer 51

PVC Criteria: - Broad QRS complex (≥ 120 ms) with abnormal morphology. - Premature — i.e. occurs earlier than would be expected for the next sinus impulse. - Discordant ST segment and T wave changes. - Usually followed by a full compensatory pause. - Retrograde capture of the atria may or may not occur - can be unifocal or multifocal and can originate from right or left ventricle (will be same pattern as LBBB or RBBB) - not requiring investigation or treatment, but may trigger the onset of a re-entrant tachydysrhythmia — e.g. VT, AVNRT/AVRT