CVPR 03-31-14 11am-Noon Arrhythmias slides - Horwitz Flashcards Preview

CVPR Unit 1 > CVPR 03-31-14 11am-Noon Arrhythmias slides - Horwitz > Flashcards

Flashcards in CVPR 03-31-14 11am-Noon Arrhythmias slides - Horwitz Deck (45):
1

Normal conduction pathway & waves generated

SA node generates an electrical impulse which cannot be seen on the ECG ---> electrical current travels through Rt. & Lt. atrial muscles and atrial depolarization is visible as the P wave ---> electrical impulse then arrives at AV node, which conducts electricity at a slower pace, creating a pause (PR interval) before the ventricles are stimulated [pause allows blood to be emptied into ventricles from atria prior to ventricular contraction] ---> QRS is due to ventricular depolarization ---> T-wave is due to repolarization

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Sinus rhythm

Ever QRS is triggered by a P wave (P before QRS)

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Normal sinus rate in adults

60-100 beats/min

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Normal PR interval in adults

0.12-0.20 seconds

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Normal QRS in adults

Whereas the QRS is normally narrow, if there is widening of the QRS (as occurs w/bundle branch blocks) but there is a P wave preceding each QRS by a normal PR interval, the rhythm is still sinus…… If the rate is 60-100, the QRS is regular, or only varies slightly due to respiration, and each QRS is preceded by a normal P wave with a normal PR interval, it is normal sinus rhythm.

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Sinus Tachycardia - causes

Commonly occurs during exercise or emotional stress, with no treatment generally needed (appropriate compensatory increase in HR)….. In pts w/coronary artery disease as well as in hyperthyroidism, the increased cardiac oxygen demand may precipitate angina …… May also be caused by hypotension, acute lung/abdominal pathology, Thyrotoxicosis

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Sinus Tachycardia – typical rates & ECG findings

Regular, fast …..Typical rates are 101-150…..Normal P & QRS

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Sinus Tachycardia – treatment

Usually none is needed, but would want to look for underlying disease if it occurs at rest….. If treatment needed (as in thyrotoxicosis), beta blockade is usually effective

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Sinus Bradycardia - causes

Common in normal individuals, especially athletes; Vagotonic states (faint; sick sinus syndrome; small inferior infarctions which increase vagal tone)

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Sinus Bradycardia – symptoms

Can cause syncope, lightheadedness or fatique in elderly patients w/age-related dysfunction - the ‘sick sinus syndrome’

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Sinus Bradycardia – typical rates & ECG findings

Regular, slow HR (<60bpm)….. P waves precede QRS, as normal

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Sinus Bradycardia - treatment

Often requires no treatment; However, it may produce syncope during intense vagal activation as in fainting (‘Vaso-Vagal event’), for which atropine is effective. Treatment of sick sinus syndrome may require placement of an electronic pacemaker.

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First-degree AV block – ECG findings

PR interval prolonged (>0.2 s, or more than one large block) = increased junctional delay

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First-degree AV block – causes

Most commonly drug-induced (beta-blockers, some Ca2+ blockers [diltiazim, verapimil], digitalis. Also, conduction system disease

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First-degree AV block – severity of the problem

Benign condition, but can proceed to more serious type of block

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Second-degree AV block - causes

Some P waves conduct normally to the ventricles, but some do not (patterns vary…. Some P waves not followed by QRS; may or may be change in PR interval in normal P/QRS)….. May reflect conduction system disease, high vagal tone, or excessive effects of drugs

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Second-degree AV block – symptoms

If rate is too slow to support cardiac output adequately, syncope or confusion may occur, requiring a pacemaker

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Second-degree AV block - Mobitz type 1 vs. type 2

Mobitz 1 type: PR gets longer & longer until a P does not conduct (no QRS) = usually less severe….. Mobitz 2 type: no change in PR, just P waves sometimes not followed by a QRS (generally more sever & worry about transition to 3rd degree AV block)

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Third-degree AV block – causes

Due to AV node or “junctional” failure with aging, infarct, severe conduction system disorders or disruption during cardiac surgery; Rarely drug-induced

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Third-degree AV block – On ECG + symptoms/outcomes

Complete Heart Block…. Both Ps & QRSs show regular rhythm, but they are at different rates, with P rate > QRS rate…. No relationship between P and QRS waves (a pacemaker below the AV node has taken over)….. May cause syncope or sudden death

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Third-degree AV block – treatment

Pacemaker if ventricular rate or BP are to low (probably a permanent pacemaker)

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Premature atrial beat/contraction

Typically an abnormally-shaped P wave before a normal,narrow QRS, w/out widening of PR …. Usually benign

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Premature ventricular beat/contraction

Typically QRS widens substantially and has no P wave in front of it….. Ectopic Ventricular Focus – conducted by slow myocardium (no Purkinje)….. Short path length blocks Re-entry …..Usually benign

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Premature Atrial/Ventricular Contractions

Both are common in healthy persons and are experienced as single-beat palpitations….. Most commonly noticed at rest when low HR permit occurrence of premature ‘skipped beats’ and when distractions are reduced allowing awareness.

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Atrial flutter – findings

P waves (flutter waves) at a rate of 240-320 bpm….. Pulse may be regular (most commonly) or irregular….. sawtooth pattern ….. Ventricular rates vary widely, but are typically rapid if untreated

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Atrial flutter has some risk of...

Embolic stroke due to clot in left atrium (not as common an outcome as it is in atrial fibrillation)

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Atrial flutter – treatment

Anticoagulation for embolism risk; Rate control w/drugs (beta-blockers, Ca2+ channel blockers - not the-pines, rather verapamil & diltiazem); Cardioversion; Ablation of reentry site

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Atrial Tachycardia – symptoms/findings

Quite uncomfortable & disturbing….. Rapid HR: at Baseline = 70; during episode = 180….. Narrow QRS complexes with P waves present before but abnormal

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Atrial Tachycardia - Treatment

Easily terminated by adenosine infusion… But, recurrence common, which can be prevented by ablation of the reentry pathway…. Also, vagal maneuver (cold towel on face) to decrease HR; beta blocker; or verapamil/diltiaem

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Atrial fibrillation - findings

Irregularly irregular ventricular rhythm (completely irregular QRS)- typically fast if not on drugs….. NO P waves at all…. May be either a chaotic or create an undulating baseline

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Atrial fibrillation –causes

A ton of impulses hitting the AV node every minute; only some can be conducted, whenever AV node is able….NI subjects (“lone A fib”); Aging (common); Post-Op; Heart disease (common); Hyperthyroidism

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Atrial fibrillation – problems/symptoms caused

Rapid HR (---> syncope, ischemia, HF)….. Loss of Atrial Kick (---> HF)….. Atrial Thrombi (---> embolic stroke)

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Atrial fibrillation – treatments

Most patients are anticoagulated & given rate control drugs, b/c of high recurrence rate of A fib….. May also require cardioversion (electrical shock or drugs; must first be anticoagulated if there is a clot) or ablation (not as successful as in flutters)

34

Anticoagulation in Atrial fibrillation

Usually wararin is used, but aspirin may be used in low-risk cases…..nearly all pts are anticoagulated b/c of risk for embolic stroke

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Rate control drugs in Atrial fibrillation

Beta-blockers…..some Ca2+ channel blockers (diltiazem or verampamil)….. Digoxin …. Singly or in combo)

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Cardioversion in Atrial fibrillation

Conversion to sinus rhythm can be achieved w/electrical cardioversion drugs or w/drugs…… However, maintenance of sinus rhythm often requires drugs with high toxic potential ---> thus, generally reserved for pts in whom rate is poorly controlled, there are intolerable palpitations, or who need their “atrial kick” to maintain cardiac output…… Pts w/out underlying heart disease or patients who have minimal evidence of pathology may also be cardioverted for AF b/c of better results in maintaining sinus rhythm.

37

Reentry Arrhythmias

Abnormal reentry pathways may be present in the atria, ventricles, or the junctional tissue…. While arrhythmias may arise from a single ectopic pacemaker, most ectopic rhythms arise from reentry

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Mechanism of Reentry

In normal heart, arrhythmias are self-terminating b/c depolarization at a junction usually meets tissue which has already been depolarized & is therefore refractory to reentry…… BUT, if chamber dilation and/or islands of fibrosis create a long & circuitous path, depolarization can continue to find non-refractory myocardium and be sustained = reentry

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Junctional Rhythms – defn.

The region surrounding the AV node is often termed “the junction” and rhythms originating there are called “junctional rhythms”.

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Junctional Rhythm – findings

Regular rhythm which may be slow or fast….. Narrow (normal) QRS complex….. NO antecedent P waves (buried before/after the QRS); sometimes P wave seen after the QRS

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Ventricular Tachycardia (VT) – causes/mechanism

From fibrosis, infiltrate, or dilation…..Ectopic ventricular focus – conducted by slow myocardium (no Purkinje)…. Long pathway length permits re-entry

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Ventricular Tachycardia (VT) – findings

Repetitive, wide, and abnormally shaped QRS (a bunch of hills close together)….. NO P wave usually…. Termed “sustained” if QRS last most than 30s (often life-threatening)

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Treatment of ventricular tachycardia

Lidocaine, amiodarone, cardioversion

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Life-threatening tachycardias

“Sustained” ventricular tachycardia or VF require emergency defibrillation……There is typically ABNORMAL ventricular contraction in VT & there is NO contraction in VF….. In asystole, only a straight line is seen on the ECG and prognosis is dismal.

45

Ventricular defibrillation

No consistent QRS or coordinated conjunction (no pattern at all) – will die quick if don’t shock (defibrillate)

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