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55 Cards in this Set
- Front
- Back
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What is an arrhthmia?
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A disturbance in rate, rhythm, site of origin or conduction of electrical impulses
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What are two mechanisms of arrythmia formation?
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1) Impulse formation disorders: Abnormally fast or slow discharge of normal pacemaker or emergence of ectopic pacemaker that overrides SA node to gain control of atrial or ventricles. Can be due to depressed or enhanced normal automaticity, abnormal automaticity, or triggered activity.
2) Impulse conduction (either a block or a rerouting of electrical impulses, such as reentry) |
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What clinical sign is caused by depressed automaticity of the normal pacemakers? Enhanced automaticity?
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Depressed = bradycardia
Enhanced = tachycardia |
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What causes abnormal automaticity?
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Damaged cell membranes in myocardial cells --> automaticity in random cells. If rate of this depolarization is greater than the rate of the SA node, it manifests as ectopic tachycardia.
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What is triggered arrhythmia?
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Abnormal impulses that are proceded by normal cardiac depolarization. Caused by small amplitude afterdepolarizations occuring during or just after the cell has repolarized.
Early afterdepolarization (EADs) occur early in repolarization (phase 2 or 3). Delayed afterpolarizations (DADs) occur during phase 4 once repolarization is complete. |
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What clinical sign is caused by impulse conduction blockage?
Impulse conduction rerouting? |
Blockage: usually --> bradycardia
Rerouting: usually --> tachycardia |
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What is classic re-entry?
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Antegrade (forward) unidirectional block + slow conduction retrograde (backward) through the block + rapid repolarization (short refractory period)
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True or false:
ECG allows you to determine the cause of the abnormality that causes arrhythmia. |
False. ECG may not allow a determination of the abnormality mechanism.
Most important mechanism overall = macro or micro re-entry circuits |
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What is a premature beat?
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Ectopic beats that override the SA node and assume control of the heart rate for one or more beats.
R-R interval from the preceding normal beat to the ectopic beat is SHORTER than the prevailing R-R interval. These manifest as tachycardic arrythmias. |
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What is an escape beat?
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Ectopic beats that occur after a pause in the sequence of normal beats.
The R-R interval from the preceding normal beat to the ectopic beat is LONGER than the prevailing R-R interval. Occurs because the SA node fails to discharge or its impulse is improperly conducted. Don't treat these! They are keeping the patient alive! |
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What are some possible causes of sinus tachycardia?
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High sympathetic tone (excitement, fear, stress)
Fever Pain Hyperthyroidism Anemia Shock Heart failure Tx with bronchodilators or catecholamines (dopamine, dobutamine) |
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What are some possible causes of sinus bradycardia?
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Elevated vagal tone (athletic conditioning, increased IC pressure, severe GI or resp. dz)
Parasympathetomimetic drugs (digoxin) Sypatholytic drugs (atenolol) Use of sedatives Hypothermia Hyperkalemia Sick sinus syndrome Severe hypothyroidism Due to depressed normal automaticity of the SA node. |
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What causes sinus arrest?
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SA node fails to depolarize, leading to a pause in the heart rhythm. Longer periods of arrest may lead to weakness, syncope.
Due to: Excessive vagal tone Sick sinus syndrome Hyperkalemia |
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What is a junctional escape?
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The AV node is acting as the pacemaker.
Normal QRS-T, but might see an inverted or retrograde P wave before or after the QRS complex due to AV node impulse traveling backwards through the atria. |
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What is the treatment for junctional escape?
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Vagolytic agents (atropine) to increase sinus rate, possibly pacemakers for SSS or AV node block.
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What is a ventricular escape beat?
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The bundle branches or Purkinje fibers are acting as pacemakers.
Because beat originates midway along ventricular conduction system, sequence of depolarization is altered, resulting in QRS-T being, WIDE, BIZARRE, and TALL. |
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What causes supraventricular premature beats?
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An ectopic pacemaker in the atria or junction area.
The impulse travels from there through the AV node and through the normal ventricular conduction path. |
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What is the difference between an atrial premature beat and a junctional premature beat?
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The APC P wave will be altered, but not inverted.
A JPC will have an inverted P wave. |
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When should you treat supraventricular premature beats?
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If there are paroxysms of supraventricular tachycardia.
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What processes may result in supraventricular premature beats?
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Atrial myocardial disease (inflammatory/degenerative)
Stretching secondary to increased atrial pressure or volume (AV valvular insufficiency) |
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True or false:
After a supraventricular premature beat there will be a non-compensatory pause with resetting of normal SA node automaticity. |
True
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What is the physiologic cause of ventricular premature beats?
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They originate in the bundle of His or Purkinje fibers in damaged myocardium.
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What will an ECG show in a case of VPCs?
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Abnormal QRS-T without corresponding P.
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What diseases process can cause VPCs?
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Inflammation, structural, toxic, infiltrative, traumatic, or ischemic heart disease.
Also: GDV Splenic disease Hyperthyroidism Sepsis Anemia Hypoxia Coagulopathies Digoxin Anesthetics Catecholamines Excessive sympathetic tone |
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How can you tell if VPCs have a unifocal or multifocal origin?
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Unifocal = uniform morphology of premature beats
Multifocal = variable morphology of premature beats |
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What is a compensatory pause?
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The pause that occurs after a VPC before the subsequent sinus beat due to inability of ventricle to repolarize before the next normal sinus beat.
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What is the treatment for VPCs?
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IV lidocaine or procainamide or oral esmolol to rapidly suppress VPCs.
Oral maintenance therapy with procainamide, quinidine, mexiletine, atenolol, sotalol, or amiodarone |
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What is supraventricular tachycardia?
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3 or more supraventricular premature beats occurring in succession.
Rapid and regular P-QRS-T rhythms. Usually due to re-entry |
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What is the treatment for supraventricular tachycardia?
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Vagal maneuvers (carotid sinus massage, sharp blow to chest wall)
IV vasopressors (phenylephrine, methoxamine) IV boluses of digoxin, diltiazem, atenolol, esmolol, or procainamide. Can also try electrocardioversion under anesthesia. |
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True or false:
Atrial fibrillation is one of the most common abnormal rhythms. |
True
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What is atrial fibrillation?
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Chaotic and unorganized atrial depolarizations, caused by multiple re-entry circuits.
Inability to produce effective atrial contractions as a result = no P waves |
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3 hallmarks of atrial fibrillation?
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Absence of P waves
Normal QRS-T Irregularly irregular QRS-T complexes |
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What causes atrial fibrillation?
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Most often secondary to severe atrial enlargement and underlying heart disease.
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How do you treat atrial fibrillation?
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Digoxin, then go to oral diltiazem/atenolol
If primary AF, can use oral or IV quinidine or procainamide to convert to sinus rhythm. |
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What is ventricular tachycardia?
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3 or more VPC's occurring in succession.
Bad news! |
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What are fusion beats?
Capture beats? |
Fusion beats: SA + ectopic depolarization of ventricles simultaneously
Capture beats: Sinus impulse "captures" ventricles, interrupting ventricular tachycardia These can both exist if the AV nodal conduction is still intact. |
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What is the treatment for ventricular tachycardia?
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Can try IV lidocain, procainamide, or beta-blockers, after correcting electrolyte imbalances.
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What does atrial flutter look like on ECG?
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Prominent baseline undulations ("saw tooth" baseline)
QRS-T waves are normal in morphology when they do occur P waves are visible |
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What is accelerated idioventricular rhythm?
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A form of ventricular tachycardia that is not tachycardic.
Normal sinus beats and VPCs alternate. Seen with GDV, splenic disease, traumatic myocarditis, and neurologic disease. |
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What is the treatment of choice for ventricular fibrillation?
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Defibrillation!
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What is an AV block?
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A delay or blockage of impulse through the AV node or the bundle of His.
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What is first degree AV block?
What causes it? |
A delay in transmission of supraventricular impulses, but all are eventually conducted.
Due to high vagal tone, digoxin toxicity, Ca cannel blockers or beta blockers, or electrolyte abnormalities. |
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What is second degree AV block?
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Some supraventricular are not conducted to ventricles.
Similar causes as first degree AV block. P waves without corresponding QRS complexes. |
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When should you treat second degree AV block? What is the treatment?
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Treat when the AV block is high grade and there is weakness or syncope.
Treat with oral sympathomimetics Most of these symtomatic patients eventually require a pacemaker. |
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What is third degree AV block?
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None of the supraventricular impulses are reaching ventricles.
Ventricles rely on ectopic ventricular pacemaker. P waves and QRS complexes are not associated. QRS-T with abnormal morphology but regular rhythm. |
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What is the treatment for third degree AV block?
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IV isoproterenol for emergency tx
Usually need an artificial pacemaker. DO NOT use drugs that suppress ventricular escape beats (procainamide, lidocaine, atenolol, quinidine) |
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What will you see on ECG in a case of right bundle branch block?
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P and PR intervals usually normal
QRS > 0.08 seconds Right axis deviation > +150 Broad, deep, slurred, notched S waves |
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What is right bundle branch block? What treatment does it need?
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The right ventricle is depolarized by the slow transmission of impulses from the left ventricle and left bundle branch.
Treatment is not required since cardiac function is not compromised. |
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What will you see on ECG in a case of right bundle branch block?
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P wave and PR intervals usually normal
QRS > 0.08 seconds MEA usually normal Broad, slurred, notched R waves |
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What ECG abnormalities can you see with sick sinus syndrome?
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Sinus arrest
Sinus bradycardia SA block Supraventricular tachycardia AV node block Abnormal conduction Abnormal automaticity |
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What causes atrial standstill?
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Caused by destruction of the atrial myocardium or severe hyperkalemia.
The atrial myocardium becomes unresponsive to sinus impulses and does not depolarize. Secondary pacemaker takes over |
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What does atrial standstill look like on ECG?
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Absence of P waves, slow regular junctional/ventricular rhythm
If due to hyperkalemia, may have tall, tented T waves and/or prolonged QRS |
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What is the treatment for atrial standstill?
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Correct electrolyte abnormality
Artificial pacing needed for idiopathic dz |
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What are some mechanisms that suppress abnormal automaticity?
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Lower the RMP
Decreasing the slope of phase 4 in diseased cells, lower the rate that action potentials occur. Raise the threshold potential. |
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What are the mechanisms that can be utilized to interrupt reentry circuits?
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-Get rid of the unidirectional block
-Turning the unidirectional block into a bi-directional block -Altering the conduction velocity around the circuit and within the damaged tissues -Altering the time the surrounding normal cardiac tissues take to repolarize |
