12-lead Interpretation Flashcards
What are the 5 steps of 12-lead interpretation?
Step1: Confirm diagnositc quality • amplitude = 1millivolt/sec • frequency = 0.05-40Hz • paper speed = 25mm/sec • all lead tracings present & eligible, aVR indicative
Step 2: Determine ECG rhythm & rate • HR • Regularity • P-wave morphology • PR interval • QRS width
Step 3: Determine ischaemia, injury or infarction
Step 3a: Systematically scan for ST elevation
Step 3b: Systematically scane for ST depression, T wave inversion or peaked T waves
Step 4: If ST elevation, consider STEMI imitations • LBBB • Ventricular pacemaker • Ventricular escape rhythm • Pericarditis • L) Ventricular Hypertrophy • Early repolarisation syndrome • Ventricular aneurysm
Step 5: Systematically state interpretation • Rhythm • Rate • Abnormalities • Interpretation
What does the ST segment & T wave represent & why is it important?
Repolarisation.
Mycordial cell membrane ion pumps are highly dependent upon O2 to move ion across the cell membranes, so any poorly perfused myocardial tissue will result in ischaemia, injury or infarction. This results in changes to the ST segment & T wave
What are four ECG changes thst are signs of acute ischaemia, injury or infarction?
- ST segment elevation
- ST segment depression
- Peaked T waves
- Inverted T waves
Where is the J point?
The junction between the end of the QRS complex and beginning of the ST segment
What is the best way to determine the isometric line when looking at ST changes?
Project the TP segement back towards the previous QRS complex
How far past the J point should ST elevation or depression be measured?
0.08sec (2mm or 2x small boxes)
How is ST depression be indicated?
Ischaemia indicative if ST depression is ≥ 1mm in any lead
How is ST elevation determined an ECG?
≥ 1mm in limb leads or > 2mm in chest leads with exception of V1 which may have 2mm as a normal variant
** AMI indicated if ST segement elevated ≥ 1mm in two or more contiguous limb leads OR > 2mm in two more contiguous chest leads
In whatt lead is it normal to have inverted T waves?
aVR
What is deemed as an abnormal Q wave? & what is it an indicator of?
When they have a depth greater than 25% (¹/4) of the height of the following a R wave.
Indicates full transmural necrosis which occurs well after ischaemic signs of the ST segment or T waves changes
What are the major corony vessels which affect the inferior region of the heart? What are the leads that face these?
- R) coronary artery
- marginal braches
II, III, aVF
What are the major corony vessels which affect both the septal & anterior region of the heart? What are the leads that face these?
Left anterior descending
V1-V4
What are the major corony vessels which affect the septal region of the heart? What are the leads that face these?
- Left anterior descending
- Septal perforator branches
V1 & V2
What are the major corony vessels which affect the anterior region of the heart? What are the leads that face these?
- Left anterior descending
- Diagonal branches
V3-V4
What are the major corony vessels which affect the lateral region of the heart? What are the leads that face these?
- Left anterior descending
- Diagonal branches
- Circumflex branches
I, aVL, V5, V6
What are contiguous leads?
Leads that are anatomically adjacent to each other in their view of the heart
i.e II & aVF
State the region of the heart, leads & reciprocal leads
Inferior - II, III, aVF ▪︎I, aVL Extensive anterior (both septal & anterior) - V1-V4 ▪︎ II, III, aVF Septum - V1 & V2 ▪︎None Anterior - V3 & V4 ▪︎ None Lateral - I, aVL, V5, V6 ▪︎ II, III, aVF
Name 9 conditions that mimic STEMI
• LBBB • Wide complex ventricular rhythms - Artificially paced ventricular rhythms - Ventricular escape rhythms & ventricular tachycardias • Pericarditis • Dissecting thoracic aneurysm • Left ventricular syndrome • Early repolarisation syndrome • Ventricular aneurysm
Explain LBBB
A block in conduction through the LBB in which impulses to the ventricles & ventricular repolarisation becomes asynchronous, with the L) ventricle depolarising later than the R). This results in a wide QRS & subsequent abnormal repolarisation, which manifests as abnormal ST segments & T waves.
What are the classic ECG signs of LBBB?
- Supraventricular in origin
- QRS > 0.12
- ‘M’ shaped QRS in V6
- Last section of QRS (i.e from J-point backwards) points downward in V1
In pts presenting with LBBB what must Paramedics reply upon to make a clinical decision?
Clinical Hx & pt presentation
What are the classical ECG findings of a RBBB?
- Rhythm is supraventricular in origin
- QRS >0.12sec
- Last section of QRS (i.e from J point backwards) points upwards in V1
Why is it that RBBB do not typically show ST segment abnormalities?
The vectors of ventricular repolarisation are not significantly altered due to to relatively smaller muscle mass of the R) ventricle
Name two examples of wide conplex ventricular rhythms that mimic STEMI
- Artficially paced ventricular rhythms
* Ventricular escape rhythms & ventricular tachycardias
Explain artificially paced ventricular rhythms
An artificially implanted device that causes abnormal depolarisation, often indicated by a wide QRS complex followed by abnormal vectors of repolarisation, manifesting as ST segment & T waves changes. It is commonly recognised by pacemaker spikes on an ECG strip prior to the QRS complex and may only be seen in particular leads.
Explain ventricular escape rhythms and ventricular tachycardias
Ventricular depolarisation at an intrinsic rate of 15-40 due to the failure of impulse conduction from the atria or junction to the ventricles.
The intrinsic depolarisation is triggered by an ectopic focus within the ventricles which triggers an abnormal wave of depolarisation across the ventricles resulting in wide QRS, and followed by abnormal vectors of repolarisation, manifesting as ST & T wave changes
What are two common types of ventricular escape rhythms?
- Complete heart block
* Idio-ventricular rhythms
Can wide complex tachycardias be used to determine STEMI?
No
What are the common cardiac symptoms/findings with Pericarditis (inflammation of the pericardium)?
- Sharp & severe chest pain (pleuretic)
- Increased with supine posturing, breathing & swallowing
- Partially elevated with sitting & leaning forward
- May have associated pericardial friction rub on auscultation
What are the common ECG findings of Pericarditis?
- ST segment elevation - usually global (90%)
- If localised, will not show reciprocal changes
- ST segments usually concave or saddle back
- PR interval depression may be indicative
What vessels are affected by occlusion if the ascending aorta dissects in a way that results in cardiac symptomology and ECG changes consistent with STEMI?
Left or right coronary artery sinus
What are the typical chest pain symptoms/findings associated with a dissecting thoracic aneurysm?
- Sharp/tearing pain
- Migratory in approx 70% of cases
- Poor relief with narcotics
- Hx ongoing hypertension
- Rare is <50yrs
- May he accompanied by symptoms consistent with CVA
Can pts with a dissecting thoracic aneurysm have ECGs consistent with STEMI?
Yes. May be difficult to discern
What is left ventricular hypertrophy (LVH)?
Enlargement of the left ventricle often secondary to chronic hypertension or aortic stenosis. Causes stronger depolarisation impulses towards the left.
What ECG findings are consistent to LVH?
• Tall QRS complexes in lateral leads - particularly I, V5, V6A • R waves > 30mm in V5, V6 • Deep S waves in V1, V2 • ST segment consistent with rise of 2mm
Characteristics of benign early repolarisation
- Healthy, young adults
- ST segment changes of 1mm
- Not localised to any lead grouping
- No reciprocal changes
- Clear concave shape
Why is Hx taking important with descerning a ventricular aneurysm?
It is difficult to tell purely based on an ECG rhythm. If there is no Hx of a recent AMI, and there are changes in the ECG relative to STEMI, then you must have a low tolerance for suspension
