CARDIO: Arrythmias Flashcards
Atrial flutter, note the sawtooth pattern
Note: In atrial fibrillation, the atria beat irregularly. In atrial flutter, the atria beat regularly, but faster than usual and more often than the ventricles, so you may have four atrial beats to every one ventricular beat.
What conditions should you keep in mind when seeing a pt with newly dx’d afib?
Mitral valve dysfunction, LV failure, CAD, OBESTITY and OSA, COPD, hyperthyroid, druggy drug drugs
a common congenital abnormality where a muscle remnant makes an additional electrical connection between the atrium and the ventricle. In these individuals, the ventricle can be excited prematurely (“pre-excited”) through a non-decrementally conducting pathway, changing the pattern of the QRS (see figure).
Wolff-Parkinson-White syndrome
What is the cardiac conduction pathway order?
SA–> AV–> His–>purkije
Initiation of the cardiac rhythm typically begins at the SA node, so the rhythm set by the SA node is called the sinus rhythm.
The electrical impulse then travels to the AV node, which acts as a conduction delay to prevent the atria and the ventricles from contracting simultaneously. This delay is seen as the PR segment on an electrocardiogram (ECG) strip.
From the AV node, conduction travels to the bundle of His, where it splits into two branches in the interatrial septum to form the left bundle branch and the right bundle branch.
The signal then travels down to individual myocardial cells via Purkinje fibers.
What are the common locations of conduction delay when thinking about heart block?
Between the sinus node and atrium (SA dysfunction)
Between the right atria and ventricles (AV block)
Below the bundle of His (infra-Hisian block)
The most common cause of SA node dysfunction is
fibrosis of the node as part of aging
Other causes include drugs (eg, β-blockers, nondihydropyridine calcium channel blockers, digoxin, some antiarrhythmic drugs).
How are the PR and P-P intervals impacted in SA nodal dysfunction (previously sick sinus syndrome) ?
The PR interval is usually normal because the AV node is unaffected. However, the P-P interval is variable because the SA node impulse can be dropped or delayed. In Figure 2, note the dropped P wave and subsequent dropped QRS complex (“sinus pause”).
Why is the PR interval unchanged in SA node block?
The PR interval is unchanged in SA node block because the AV node is unaffected.
First-degree AV block is defined as a prolonged time between atrial depolarization and ventricular depolarization, leading to a PR interval of more than ______ seconds.
0.2
Why might you see PR delay in athletes?
Another common cause of first-degree AV block is a physiologic conduction delay in highly conditioned athletes with slow heartbeats (and normal hearts). Normally, when the heart rate slows, the vagal system also slows conduction at the AV node. In these athletes there may be an asymptomatic PR delay longer than 0.2 seconds, which is technically considered a physiologic first-degree AV block. There is no disease or treatment needed.
What makes second degree AV block different from 1st?
Specifically, in second-degree AV block, some (but not all) atrial impulses are unable to reach the ventricles.
What re the two types of 2nd degree AV block?
Mobitz 1 and 2
most patients with Mobitz type II present with symptoms, including
fatigue, dyspnea, chest pain, and syncope.
Most patients with mobitz 1 clinically present…
Most patients with Mobitz type I heart block are asymptomatic.
Mobitz type II is almost always caused by cardiac disease, including….
Mobitz type II is almost always caused by cardiac disease, including MI, cardiomyopathy, and myocarditis (especially Lyme disease).
It can also be caused by hyperkalemia.
Mobitz type II is often worsened by drugs that affect the AV node such as β-blockers, nondihydropyridine CCBs, and digoxin.
What would you expect on ECG for mobitz 1?
Mobitz type I presents with progressive lengthening of the PR interval until a QRS beat is dropped
What would you expect on ECG with mobitz 2?
Mobitz type II presents with constant PR intervals followed by random, intermittent dropped QRS beats
How can you differentiate mobitz 1 and 2?
Pay attention to PR interval on ECG
Treatment for mobitz 2
pacemaker
Why might patietns with severe AV dissociation have widened QRS complexes?
Patients with severe AV dissociation may have a widened QRS complex due to conduction beginning in the ventricles (below the AV node).
Clinical presentation of RBBB
RBBB is typically asymptomatic.
What conditions might cause a RBBB?
Causes include right ventricular hypertension (cor pulmonale), right ventricular infarction, myocarditis, pulmonary embolism (leading to pulmonary hypertension and high right ventricular pressure), or medical procedures involving the right heart, such as right heart catheterization.
How do you ID LBBB on ECG?
A notched R wave, without a Q wave, in lead V6 is indicative of LBBB
presents with progressive lengthening of the PR interval until a QRS beat is dropped; patients are typically asymptomatic and do not require treatment.
Mobitz type I second-degree AV block (Wenckebach)
presents with constant PR intervals followed by intermittent dropped QRS beats; patients are treated with a pacemaker because of the risk of deteriorating into third-degree heart block.
Mobitz type II second-degree AV block
occurs when P waves do not lead to QRS complexes, causing a slow ventricular escape rhythm.
Third-degree AV block, or complete heart block
What symptoms are typically present with type I second-degree atrioventricular block?
No symptoms
A patient presents to the emergency department for evaluation of a syncopal episode. He describes a sudden blackout from which he recovered after a few seconds of lying down. His heart rate is 45 beats/min. The ECG shows normal P wave morphology. The P wave rate is 80/minute, while the QRS rate is 45 beats/min. What kind of heart block?
The distinct, unrelated P and QRS rates suggest complete (third-degree) heart block in this patient. This ECG finding is known as AV dissociation and is unique to complete heart block because no atrial impulses are transmitted to the ventricles.
What heart block: AV dissociation
3rd degree heart block
Dropped p waves are characteristic of
Mobitz type I and type II second-degree heart block
Prolonged PR interval characterizes
first-degree heart block
Wide QRS complexes are seen with …
any heart block that affects conduction below the bundle of His.
How does carotid massage help alleviate symptoms of PSVT?
The nerve of the carotid sinus (nerve of Hering) is a branch of the glossopharyngeal nerve (CN IX) that terminates in the vasomotor center of the medulla oblongata (nucleus tractus solitarius). Carotid sinus massage stimulates baroreceptors, which transmits a signal to the medulla oblongata via CN IX. The efferent signals from the medulla to the myocardium are conducted via the vagus nerve (parasympathetic supply), which results in ↓ AV nodal conduction, ↓ heart rate, ↓ contractility, and vasodilation (↓ blood pressure).
