User:Bron766/My Portfolio/ECG

Here are my ECG notes. They are not complete, lack references and should not be relied upon to be accurate.

Rhythm
Rhythm is the order or sequence in which the parts of the heart are electrically activated.

Sinus rhythm and its variations
A normal P before each qrs, regular, 60-100 bpm. Sinus variants :
 * Asystole
 * Sinus tachycardia (>100 beats per minute)
 * Sinus bradycardia (<60 beats per minute)
 * Sinus arrest or pause
 * Sino-atrial exit block
 * Sick Sinus Syndrome
 * Sinus Arrythmia

Premature beats
Premature contractions come too early.
 * Premature Atrial Complex (PAC)
 * Ventricular Ectopic Beat (VEB)

Escape beats
Escape beats/rhythms come too late.
 * Atrial escape (abnormal p)
 * Junctional escape (narrow, no p)
 * Ventricular escape (slow, wide)
 * Accelerated idioventricular rhythm (ventricular but faster intrinsic rate, e.g. in MI reperfusion)

Tachycardias
Abnormal fast rhythms (generally enhanced automaticity or re-entrant circuits).

Narrow complex tachycardias
Supraventricular: sinus tachycardia (most common, e.g. PE), atrial tachycardia, atrial flutter, junctional tachycartdia (no p or very close).

Wide complex tachycardias
VT (started by VEB? Very wide, LAD, fusion beats, praecordial concordance) or SVT + aberrant conduction. (QRS <140, p waves associated…). Torsades de Pointes. Electrolyte imbalances (K). Toxins eg TCA, CCB.

Differentiating VT from SVT with aberrancy:
 * AV dissociation (VT)
 * Fusion / capture beats, P waves dissociated from QRS
 * Intermittent Canon a waves, variable S1 and BP beat to beat
 * Age
 * VT if >35 (92% sens, 85% pos pred)
 * History of MI/angina/CCF – VT
 * Haemodynamic instability IS NOT A SIGN OF VT vs SVT and may lead to misdiagnosis
 * Brugada criteria
 * Absence of RS complexes
 * Long RS nadir >100msec
 * AV dissociation
 * Concordance?
 * LBBB morphology: VT more likely if V1 R >30msec or S broadly downsloping >60msec and notched
 * RBBB morphology: VT more likely if V6 R/S ratio less than 1 (negative)?
 * Any Q wave in V6 - VT
 * irregular wide tachycardias: AF + BBB / accessory,, Flutter with aberrancy and variable conduction,mPolymorphic VT, Artefact (e.g. tapping lead)
 * If in doubt treat for VT instead of SVT: SVT meds like verapamil cause haemodynamic instability and don’t fix the rhythm. VT meds may fix the rhythm and won’t increase risk of instability. Adenosine can precipitate VF if AF + WPW

Axis
What is a 'cardiac axis'? The cardiac axis is the overall direction that the heart is electrically activated in. You can illustrate the cardiac axis by drawing a single arrow on the surface of the body to represent the strongest direction of heart activation. For some people, it is normal for this direction to travel vertically down the body. For other people, a normal direction of activation is horizontal from right to left, or even angled slightly up towards their left shoulder. Because there is so much difference between people, we have defined a normal axis range rather than only one specific angle.

Why does it matter?
The cardiac axis gives an overview of the heart's activation. Some major abnormalities can make the axis swing to a whole new direction, such as damage from heart attacks or enlargement of the right heart side from lung disease.

What is the easiest way to check whether an ECG axis is normal or abnormal?
The easiest way of making sure the cardiac axis is normal is to check that Lead I and Lead II are both positive on a 12 lead ECG. A positive lead is one where the waves above the baseline are stronger (taller) than those below the baseline. (By contrast a negative lead or complex has deeper negative waves. An isoelectric lead has equal positive and negative waves.)

What if the axis is abnormal?
If the axis is abnormal, you need to work out whether it is pointing too far to the left (Left Axis Deviation), too far to the right (Right Axis Deviation) or whether it is just way off course (Extreme Axis Deviation). To do this you need to know which direction each lead 'looks' at the heart from. For example, lead I compares electrical readings from the right arm electrode to the left arm electrode, making the overall direction a horizontal line from right to left. By convention, lead 1 is called an angle of 0 degrees and the angle of every other lead is measured from it.

In the following pictures, pretend you are looking at a patient facing you, so your left is their right and vice versa.

Method 1: Thumbs
You will need:
 * Two thumbs (real or imaginary)

This 'rule of thumb' requires you to look at just two leads, usually I and II, and point a thumb in the direction of each lead (positive = up, or negative = down).
 * If both of these leads are positive, that's two thumbs up for a Normal axis.
 * If I and II have 'left each other', (lead I is positive and II is negative so thumbs point away), there is Left axis deviation.
 * If leads I and II are 'right for each other', (lead I is negative and II is positive so thumbs point towards each other), there is Right axis deviation.

''Caution: while this rule of thumb is easy to remember, it leaves out the area between +150 and +180, which is also still right axis deviation. In this area, lead II becomes negative but aVF is still positive. A better definition of right axis deviation is where lead I and aVF are 'right for each other'. aVF is also needed to define Extreme axis deviation, where I and aVF are both negative.''


 * [[Image:Nuvola apps bookcase.png|32px]] Read an alternative explanation of a thumbs method at mediscuss.org

Method 2: Shade the quadrants
Once you know which direction each lead looks in and you can describe a complex as positive or negative, you can work out the region that the axis is in by shading quadrants. If a lead is positive, the cardiac axis must be somewhere on the half of the chart where that arrow points.

Here is an example:

Method 3: Find the isoelectric lead
As stated above, an isoelectric lead has equally positive and negative waves in the QRS complexes. If you can find a lead that is isoelectric, the axis is at a right angle (90o) to that lead.

This method so far gives two possible angles that are both 90 degrees from the isoelectric lead (+ 90o or - 90o). To decide which angle is the correct axis, check to see if the lead closest to the axis is positive or negative.

The limitation to this method is that there isn't always an isoelectric lead to find.


 * [[Image:Nuvola apps bookcase.png|32px]] Read an alternative explanation of the isoelectric method at 'The Cardiac Axis - For 4 yr olds'
 * [[Image:Crystal Clear app package games.svg|32px]] (Once you understand the idea of the isoelectric lead, try this Axis simulator)

Method 4: Plot the complex heights
The most precise method of calculating the cardiac axis is by plotting the net (overall) complex heights from two leads.
 * [[Image:Nuvola apps bookcase.png|32px]] Read a good explanation of this method at Kansas City University of Medicine & Biosciences - ECG Primer: The Mean Electrical Axis

PR interval
The PR interval includes the P wave and the PR segment.

Normally, the PR interval begins with the activation of the sinus (SA) node in the right atrium. It then includes all of the time taken for the activation signal to travel through the atria and reach the AV node. There is a pause at the AV node, as it acts like a gatekeeper at the entrance to the ventricles. The PR interval ends when the signal finally escapes from the clutches of the AV node and enters the ventricles below.

There are several ways that this normal sequence of events can be messed up.

The PR interval can be prolonged or irregular if there are extra delays in getting through the AV node (an AV block). An AV block can either be first, second or third degree depending on how much trouble the signal has in getting through. At first, the AV node is just lazy: normal atrial signals each get through eventually, but they take longer than 200 milliseconds. In second degree block, the AV node works sometimes but also starts dropping some signals out and not letting them through. In third degree block, the AV node never works and no signals can get through from the atria to the ventricles at all. Third degree block is also called complete heart block.

There are also two different types of second degree AV block: Wenckebach/Mobitz 1 and Mobitz 2. In Wenckebach, the AV node gets progressively more and more tired with each P wave. Each PR interval gets longer and longer until it gives up, drops a beat, resets and starts the cycle over again. In Mobitz 2, the AV node drops the signal in a set pattern, e.g. cycles where two go through then one is blocked (2:1 block), or for every 3 that go through 1 is blocked (3:1).

Blocks can also occur in the SA node...

Conversely, the PR interval can be shortened if there is a shortcut way of the signal getting through the atria and down into the ventricles. Logically, a shorter journey means either starting closer to home (e.g. an ectopic beat that starts nearer to the AV node instead of at the SA node) or taking a shorter route (e.g. an accessory pathway leading straight into the ventricles instead of having to be held up at the AV node).