|ECG Low voltage
|ECG Pathological Q waves
|ECG ST/T wave changes
|ECG short PR
|ECG Heart Block
|ECG Asystole and P wave asystole
|ECG QRS complex
|ECG ST segment
|ECG: QT interval
|ECG: Bundle branch blocks
|ECG Dominant R wave in V1
|ECG Acute Coronary Syndrome
|ECG Crib sheets
- The QRS complex is the surface ECG recording of ventricular depolarisation. Any surface measurement is the net sum of all the voltages in that particular view of the heart. The wave of depolarization spreads from the AVN down into the left side of the interventricular septum. The wave then passes laterally to depolarise the right side of the septum. The LV forms the bulk of the depolarising muscle.
- The wave spreads down into the Purkinje cells and depolarises the myocardium from the inner endocardium through the myocardium to the pericardial side. Over the left-sided leads (I, aVL, V4, V5) there may be a small Q wave due to septal depolarisation away from the leads followed by a large R wave as the current sweeps down and towards the apex of the left ventricle.
- On the right side of the chest (V1, V2) this shows as an initial small r wave followed by a large S wave as depolarisation is away. QRS duration is usually quoted as < 120 ms.
- Following on from this the terminology is such that the first negative deflection is a Q wave and the next positive deflection is an R wave. If a negative deflection occurs after an R wave it is called an S wave. If the first defection is positive it is called an R wave, if there is an S wave and then a 2nd positive wave this is called an R' wave
- Shows the net direction of ventricular depolarization. There are many ways to calculate it using the limb leads. Leads I and avF are at 90 degrees. Sum the net voltage in either and using a triangle then calculate the angle of the vector. The normal axis is between -30 degrees and + 90 degrees.
- Anything beyond +90 degrees is right axis deviation which may be due to Right ventricular hypertrophy or left posterior hemiblock due to damage to the posterior fascicle of the left bundle. Anything beyond -30 degrees is left axis deviation which may be due to left ventricular hypertrophy or left anterior hemiblock due to damage to the anterior fascicle of the Left bundle.
Left ventricular hypertrophy
- The findings usually include a more leftward QRS axis. The left-facing leads show increasing voltage e.g. I,II, aVL, V5,V6 and there may be left atrial hypertrophy. With time the reverse tick ST and T wave changes occur - the sol called "strain pattern".
- There are many different classifications of ECG criteria for LVH though they all have a balance of sensitivity and specificity. Generally, an aVL > 11 mm or the deepest S wave + the tallest R wave > 40 mm in the chest leads though this varies with age. With time LBBB can develop.
Right ventricular hypertrophy
- The leads lying close to the RV such as V1 and V2 show increased voltage with even a positive R wave in V1.
- The LV leads are unchanged. There may be signs of Right atrial enlargement. With time RBBB can develop.
Left Bundle Branch Block
- An RSR' pattern in V6 is LBBB - the right ventricle depolarized first then the left ventricle
Right Bundle Branch Block
- An RSR' pattern in V1 in RBBB - the left ventricle depolarized first followed by the right ventricle
Wide QRS > 0.12 seconds (3 small squares)
- Intraventricular conduction defect (LBBB, RBBB)
- Ventricular initiation of complex e.g. Ventricular tachycardia
- Wolff Parkinson White syndrome with delta wave
- Hyperkalaemia there is widening and coarsening of the QRS complex
Increased QRS voltage (height)
- LVH S in V1 and R in V5/6 > 35 mm
- RVH Dominant R wave in V1
- Hypertrophic cardiomyopathy
Decreased QRS voltage (height)
- Obesity, Pericardial fluid
- Hypothyroidism, Emphysema
Response to new LBBB and Chest pain
- Treat as acute coronary syndrome - STEMI equivalent
- New LBBB in the setting of chest pain demands 999 call and Oxygen, Nitrates, Aspirin in the interim
- A regular broad complex tachycardia > 120/min suggests Ventricular tachycardia - urgent 999 referral