In this lesson I am going to teach you how you can uncover some things if you just dig a little.
In this lesson, we are going to perform the third and fourth steps of the six step method.
In this lesson, we will learn a few more pathologies which can be identified on a 12-lead ECG. All of these conditions listed can be identified by examining the intervals and morphologies. Lets learn how.
This is the atrial depolarization wave. In general, its height should not exceed 2.5 mm and its width should not exceed 0.10 seconds. Should be positively deflected in nearly every lead, may be biphasic in V1 as a normal finding.
The morphology of the P-wave changes depending on the site of the atrial pacemaker. Site A shows the location closes to the physiological pacemaker, the SA node. Site B shows how the pacemaker can actually be in the left atrium, and site C shows a site that could cause an inverted P-wave. If the AV junction is the primary pacemaker site, it could also cause an inverted P-wave due to retrograde conduction. Basically, the impulse is traveling in the oposite direction as it normally would, so it would be traveling away from the positive electrode, which we know will create a negative deflection on the ECG.
Ok, we are ready to talk about our first type of chamber enlargement, left atrial enlargement. This type of hypertrophy may be a result of left ventricular hypertrophy, or heart failure. The notched P-wave is a result of the left atrium taking longer to depolarize. The first hump is a result of the right atrium depolarizing, and the second hump is a result of the left atrium firing. A biphasic P-wave is a common finding in V1, and may be normal. However, if it is deeper than it is tall, this is clinically significant, and indicates left atrial enlargement.
The next type of chamber enlargement is right atrial enlargement. The pictures are an example of p-pulmonale, which is just a fancy way of saying that the right atrium is enlarged and it is usually due to right ventricular failure and enlargement which is called cor pulmonale. These tall P-waves generally have a sharper peak than the average p-wave. You may also note bi-atrial enlargement if you see this type of P-wave on a limb lead, which indicates RAE with a deep biphasic P-wave on V1 indicating LAE.
As I stated, V1 will commonly have a biphasic P-wave. If it isn ’t deeper than it is tall, it is a sign of intra-atrial conduction delay. This just means that there is some sort of non-specific delay in conduction from the right atrium to the left atrium. As far as significant pathologies are concerned, this finding doesn’t really mean much clinically.
The PR-Interval lasts from the beginning of the P-wave to the beginning of the QRS complex. You may wonder, why is it called the PR-interval and not the PQ-interval, since the Q-wave is the first wave of a QRS complex. I can only guess it is because the R-wave is usually the most prominent, and often the first wave in lead II, which is the quintessential monitoring lead. The PR-interval should be bigger than 3 small boxes, but shorter than one big box.
WPW involves a conginital accessory pathway within the atrial wall that allows a faster path of electrical conduction from the atria to the ventricles
These are the classic findings for WPW. A shortened PR-Interval, widened QRS duration, and a slurring upslope of the R-wave, known as the delta wave.
The classic findings that indicate WPW
Here is an example. The baseline is altered in a few leads, but we can still try to identify any WPW findings.
We can see a delta wave, shortened PR-Interval and widened QRS complex all in lead 1. Keep in mind that these changes will not always be preset in every lead. Look at the other leads on this rhyhm strip and see how the morphology is different amongst them.
Here is another example
In this one, V4 seems to be the best lead to find the classic WPW findings of a shortened PR-interval, and delta wave.
Think FBI The drug Cardizem is contraindicated with WPW, and if administered with WPW, Cardizem could cause a lethal arrythmia that is nearly impossible to convert. Always suspect WPW with a fast, broad , and irregular arrythmia.
LGL has a bypass tract, called the James fiber that bypasses the AV node. Normally the AV node slows down conduction to allow the ventricles to fill. This shows up as the PR-interval on the ECG. With LGL we have a shortened PR-interval because of this bypass.
7 morphology of p
12-LeadElectrocardiography a comprehensive course hologie Morp s e“ P”) (Th Adam Thompson, EMT-P, A.S.
Objectives• Review normal intervals & morphologies• Learn how to identify BBB’s.• Learn how to identify atrial enlargement or ventricular hypertrophy.• Learn how to identify WPW or LGL.• Learn how to identify electrolyte derangements.
P-Wave• Normal height < 2.5mm (2 1/2 small boxes)• Normal width < 0.10 seconds (2 1/2 small boxes
PR-Interval • PR-Elevation – Usually indicates poor baseline • PR-Depression – May indicate pericarditis – May indicate atrial infarction
Short PR-Interval• Accessory Pathway – Bypasses AV node – Predisposes patients to significant re-entry tachycardias.
Accessory Pathway• Wolff-Parkinson-White Syndrome (WPW) – Bundle of Kent – Short PR-Interval – Delta Wave, Wide QRS• Lown-Ganong-Levine Syndrome (LGL) – James Fiber – Short PR-Interval – Normal P-wave, Normal QRS
WPW• Three conduction patterns – Physiological - Normal conduction, no changes may be noted on 12-Lead – Orthodromic - Signal travels down Kent bundle and physiological pathway. • Causes shortened PR-Interval & Delta Wave. – Antidromic - From SA Node through Kent bundle to ventricles then back to atrium via AV junction. • Causes very fast wide complex tachycardias. • Looks like V-tach.
LGLLown-Ganong-Levine Syndrome (LGL) » James Fiber bypasses the AV node. » Shortened PR-Interval.
Shortened PR-Interval• The take home message: – Recognizing the presence of an accessory pathway is much more important than the ability to differentiate between the different types of accessory pathways.