ECG Basics Flashcards
What do the X and Y axis represent on the ECG?
X axis is the time domain : 1 small square expresses a time frame of 40 ms. 1 large square expresses a time frame of 200 ms.
Y axis represent the voltage domain : 1 cm (2 large squares) is equal to 1mV, large square (5 mm = 0.5 mV), small square (1 mm = 0.1 mV).
How is an ECG calibrated? What is electrical hysteresis?
The standard calibration for ECG is 10 mm/mV. The standard speed at which the paper is running is 25 mm/s.
If the device is old there may be electrical hysteresis in which the first part of the graph is higher in voltage, voltage overestimation. The second part leads to a depression that can lead to many errors.
How are leads positioned on a 12 lead ECG?
There are lead DI (RA), DII (LA9) and DIII (LL) which represent einthovens triangle and are bipolar leads. This meaning that they use two leads one as a positive and one as a negative.
The augmented limb leads are aVL, aVR and AVF which each use one of the limb leads as one positive electrode and the mean distance of the other two as the negative lead.
The precordial leads or chest leads are VI (R4th), VII (L4th), VIII (between VII and V4), V4 (mid clavicular 5th), V5 (anterior axillary 5th), V6 (mid axillary 5th)
What are some additional leads that can be used?
Posterior leads such as V7, V8 and V9 are used to asses the state of the LV posterior wall.
Right leads (V2R, V3R and V4R) : useful in case of suspicion of right ventricular myocardial infarction or conditions involving right coronary arteries or posterior wall.
What do the ECG waves represent?
- P wave (atrial depolarization) : record of the electrical activity through the upper heart chambers.
- QRS complex (ventricular depolarization) : record of the movement of electrical impulses through the lower heart chambers (ventricles).
- ST segment shows when the ventricle is contracting but no electricity is flowing through it. The ST segment usually appears as a straight, level line between the QRS complex and the T wave.
- T wave (ventricular repolarization) shows when the lower heart chambers are resetting electrically and preparing for their next muscle contraction.
What is a diastolic murmur? How can it be assessed from an ECG?
Diastolic murmur is a noise produced by the blood flowing through diastole that can be heard during heart’s auscultation. It is usually caused by aortic regurgitation or mitral stenosis. This can cause the atria to enlarge leading to different P wave morphologies. A double peak P wave can be a sign.
Which atria is activated earlier? Which wave represents atrial activation?
Right atrium is activated firstly and then, nearly simultaneously also the left one will undergo activation process through bachmanns bundle. The two atria produce waves that are almost equal in amplitude, since the amount of myocardium is nearly the same between the two parts.
It lasts around 120 ms, three small squares.
P wave is positive in DI, DII and V3-V6, biphasic (neg < pos) in V1-V2 and negative in aVR.
Atrial activation in leads DII and V1?
In DII both atria the vectors move towards the positive electrode giving a normal P wave. In V1 the the RA which depolarizes slightly earlier points towards the lead the LA points away giving an S shaped P wave. It is useful in determining if there is a dilated atrium with respect to the other, as both the positive and negative parts should be equal.
What is noticeable of the P wave on the image?
In the ECG (right atrium enlargement), the wave produced by the right atrial component is masking all the successive left atrium’s activations. A monophasic P wave with an amplitude > 2.5 small squares in DII lead (> 0.25 mV) represents a right atrium enlargement.
What is noticeable of the P wave on the image?
The ECG represents a increase in P wave’s amplitude that is greater than threshold. The left atrial component is going up after a depression of the right one, left atrium enlargement in DII may be an option for diagnosis. Left atrium’s enlargement is more prevalent than right atrium’s enlargement. The main causes of left atrium’s enlargement can be mitral stenosis, aortic stenosis and hypertension.
What does the PQ interval represent?
The PQ interval (sometimes referred to as the PR interval as a Q wave is not always present) indicates how fast the action potential is transmitted through the AV node from the atria to the ventricles.
AV node conduction usually takes 120 to 200 ms to occur. More than 200 ms and there could be AV blockage. PQ segment is horizontal as it is isoelectric and almost nothing happens on the surface.
What is a delta wave? What is it a classical finding of?
It is the typical finding of Wolff Parkinson White syndrome. The delta wave is an accessory pathway that occurs in a shorter time frame than the normal PQ interval. It is defined as a slurred upstroke to the QRS complex which is caused by the QRS wave occurring immediately after the P wave due to premature excitation.
What is indicated by the arrow? What can be the cause?
It is a PQ depression.It can be caused by pericarditis if it is a slight depression, less than 120 ms. if the same segment was larger it could have been an indication of intraventricular conduction delay, partial or complete.
What is the QRS complex? How is the QRS axis deviation calculated?
The QRS complex is represents the depolarization of the ventricles. It’s vector caused by the depolarization of the myocytes is interpreted to clinically diagnose certain conditions. A cardiac axis is used. Normal QRS vector is between -30 degrees and +90 degrees. We look at lead I and aVF and we calculate the mean vector.
What are some pathological conditions associated to QRS axis deviation?
Right axis deviation : normal in pediatric ECG, LVH, COPD.
Left axis deviation : emphysema, WPW, hypercalcemia, ventricular pacing, left anterior vascular block.
Extreme RAD : emphysema, hyperkalemia, lead transposition, ventricular arrhythmia, ventricular pacing.
