Pathophys - Test 1 - EKG & Cardiac Arrythmias

How do you define different types of arryhthmias?
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How do you define different types of arryhthmias?
Arrhythmias are abnormal rhythms of the heart.
They are classified based on heart rate (brady or tachy)
Based on site of origin (supraventricular & ventricular)
Based on mechanism (automatic, triggered, re-entrant arrhythmias)
What is the clinical presentation of patients with arrhythmias?
Palpitations
Lightheadedness
Syncope (loss of consciousness - brief, fainting)
Nonspecific symptoms: fatigue, dyspnea, exertional intolerance
What are causes of bradyarrhythmias?
Sinus node disease, 2nd and 3rd degree heart block, bradycardia associated with pacemaker malfunction
What are the causes of tachyarrhythmias?
Ventricular tachycardia, torsades de pointes, ventricular fibrillation and supraventricular tachycardia
What symptoms tend to differentiate Bradyarrhythmias from Tachyarrhythmias?
Brady - decreased heart rate leads to syncope
Tachy - increased heart rate leads to palpitations
Both have a decrease in cardiac output
What are the conducting systems into the heart? What rates do they beat at?
SA node (70bpm)
AV node (40-60bpm)
Bundle of his (only connection b/t atrium and ventricle)
Bundle branches
Purkinje fibers
(last three at 30-40bpm)
What is the sequence of spread of cardiac action potentials?
AP originates at SA node (pacemaker)
--> AP conducts to AV node rapidly
--> AV delay occurs
--> At the same time spreads over atria slowly
--> Spread rapidly to the apex through bundle of His and bundle branches
--> Spreads rapidly over both the ventricles from apex to base through the Purkinje fibers
How do you diagnose cardiac arrhythmias?
12-lead electrocardiogram
Vagal maneuvers - carotid masage
Electrophysiological studies - the ability to trace specific pathways and map conduction
What are the standard bipolar limb leads?
Lead I, II and III
What are the augmented unipolar limb leads?
aVR, aVL and aVF
What are the unipolar chest leads?V1-6What is the P wave?Atrial depolarizationWhat is the QRS complex?Ventricular depolarization wave Set of three waves Due to changing direction of wave of depolarization in sequence (depolarization is from inside to out)What is the ST segment?Ventricles remain in depolarized state for sometime before they get repolarized (refractory state) Corresponds to plateau phase of ventricular APWhat is the T wave?Ventricular repolarization wave Repolarizes from the outside to the insideHow long is one box/1mm on ECG tracing?0.04secWhat does the PR interval indicate?Indicates AV delayWhat does the QT interval indicate?Depolarize and repolarize of the ventriclesWhat is the normal axis range for the angle of the heart? Left axis deviation? Right axis deviation?Normal: -30 and +110 degrees Left axis: less than -30 degrees Right axis: greater than +110 degrees Deviation is seen in hypertrophyWhat does the R-R interval indicate?One cardiac cycle length Gives you the heart rate Varies inversely with heart rateWhat is the quick way for estimating HR on an ECG?Starting with first solid line after the R peak 300 - 150 - 100 - 75 - 60What are the characteristics of a normal sinus rhythm?Rhythm - regular Rate - 60-100bpm QRS duration - normal (w/in 3 small boxes) P wave - 1:1 before QRS complex P-R interval - normal (less than 5 small squares) Indicates that the electrical signal is generated by the sinus node and travelling in a normal fashion to the heart.What are the two basic mechanisms for bradyarrhythmias?Reduced activity of the pacemaker Conduction blockExplain the action potential of the SA node (pacemaker)Phase 4 - unstable resting phase (If channels activate Na+ channels) Phase 0 - Upstroke - Infux of Ca2+ (Ca2+ channels open due to Na+ influx) Phase 3 - Repolarization - Outward K+ (inactivation of Ca2+ channels and increased activation of K+ channels)What is mechanism of bardyarrhythmias in reduced automaticity of sinus node?Results in a slow heart rate or pauses. If SA node activity stops - heart will be activated at a slower rate (usually AV node). Reduced sinus node automaticity can occur during periods of increased vagal tone (sleep, carotid sinus massage), increased age and secondary to drugs (beta-blockers, calcium channel blockers). Can be due to ischemia of SA node fibers.What is the effect of stimulation of Vagus (PSNS) nerve on heart?On SA node: decreases heart rate Known as negative chronotropic effect Mechanism: ACh binds with M2 receptors in SA node - causes a decrease in rate of rise of phase 4 and hyperpolarization of resting membrane potential, leading to a slower heart rateWhat is the mechanism of bradyarrhythmias in conduction blocks?The AV node and bundle of His are the most vulnerable sites for blocked conduction b/t atria and ventricles AV block can occur with: - Increased age - Increased vagal input - Congenital disorders (i.e. muscular dystrophy, tuberous sclerosis) - Acquired disorders (i.e. sarcoidosis, gout, lyme disease, SLE, ankylosing spndylitis, coronary artery disease) - Septal damage (abscesses)What are common bradyarrhythmias?Sinus bradycardia (problems w/in SA node) First-degree heart (AV) block Second-degree heart (AV) block Third-degree heart (complete AV) block (last three are conduction problems)What are the characteristics of sinus bradycardia?Rhythm - regular Rate - LESS THAN 60 BPM (Long RR interval) QRS duration- normal P wave - 1:1 ratio with QRS complex P-R interval - normalWhat are examples of sinus bradycardia?Athletic person Increased vagal tone Inferior wall MI Hypothyroidism Patient with brain injury w/ increased ICP Drug toxicity (digitalis, beta-blockers, Ca2+ channel blockers)What are the characteristics of a 1st Degree AV block?Rhythm - regular Rate - normal QRS duration - normal P wave - ratio 1:1 P wave rate - normal P-R interval - PROLONGED (> 5 small squares)What is the mechanism of a 1st degree AV block?A conduction delay through the AV node - but all electrical signals reach the ventricles. This rarely causes any problems by itself. Seen in trained athletes.What are the characteristics of a 2nd degree - Mobitz type 1AKA Wenckebach Rhythm - REGULARLY IRREGULAR Rate - normal or slow QRS duration - normal P:QRS ratio - 1:1 for 2-4 cycle, than 1:0 P-R interval - Progressively lengthening of P-R interval until a QRS complex is droppedWhat is the mechanism of a Mobitz Type 1 AV block?Conduction block of some, but not all atrial beats from getting through to the ventricles at the AV nodeWhat are the characteristics of a 2nd degree - Mobitz Type 2 block?Rhythm - regular between conducted beats Rate - normal or slow QRS duration - may be prolonged (infranodal block) P:QRS ratio - 2:1, 3:1 P wave rate - nromal but faster than QRS rate P-R interval - normal or prolonged BUT CONSTANTWhat is the mechanism of a Mobitz Type 2 AV block?Electrical excitation sometimes fails to pass through the AV node or bundle of His downwards. Electrical conduction of the conducted beast is the same always (hence they have a constant P-R interval).What is the characteristics of a 3rd degree block: Complete AV block?Rhythm - regular Rate - slow QRS duration - prolonged P wave - UNRELATED TO QRS (AV dissociation) P wave rate - normal but faster than QRS rate P-R interval - variationWhat is the mechanism of a complete AV block?No atrial impulses pass through the AV node. Ventricles generate their own impulse through an 'escape mechanism' from a focus somewhere within the ventricle at a regular, slow rate.What are the basic mechanisms for tachyarrythmias?Increased automaticity of pacemaker Spontaneous depolarizations (secondary to irritation) Re-entrant circuit - most commonWhat is the mechanism of tachyarrhythmias in increased automaticity of the pacemaker?More rapid phase 4 depolarization of the action potential of SA node leads to a faster heart rate.What are potential cause of tachyarrhythmias?Hyperthryoidism Anxiety/fright Pheochromocytoma Pulmonary embolus Exercise Stress FeverWhat are the characteristics of sinus tachycardia?Rhythm - regular Rate - MORE THAN 100 BPM QRS Duration - normal P wave - 1:1 QRS P-R interval - normalWhat is the mechanism of sinus tachycardia?The impulse generating the heart beats are normal, but they are occurring at a faster pace than normal.What is the mechanism of tachyarrhythmias in sponatenous depolarizations?If repolarization is delayed (longer plateau period), spontaneous depolarizations (EAD/DAD) can occur in phase 3 or 4 of the ventricular/atrial action potential. These depolarizations can repetitively reach threshold and cause tachycardia.Summarize the ionic basis of phases of AP from ventricular muscle fibersPhase 0 - upstroke of AP (transient increase in I(Na) channels) Phase 1 - brief period of initial repolarization (negative outward current) Phase 2 - plateau phase (inward Ca2+ flux) Phase 3 - repolarization (outward K+ flux) Phase 4 - resting membrane potentialWhat are examples of tachyarrhythmias from spontaneous depolarizations?Long QT syndrome (due to several specific ion channel defects) Torsades de pointes Class III antiarrhythic drugs block K+ channels and at toxic doses may produce tachyarrhythmiasDefine Long QT syndromeReduced function of potassium channels leads to a prolonged plateau period, leading to a prolonged QT interval (can be congenital or induced (i.e. electrolyte imbalance)) Prone to triggered activity because of reactivation of sodium and calcium channels (early afterdepolarizations (EAD)) Triggered activity in the ventricles can lead to life-threatening ventricular arrhythmiasDefine Torsades de pointesA "twisting," polymorphic ventricular tachycardia A specific type of triggered arrhythmia that is observed in situations where QT interval has been prolonged The cardiac arrhythmia may cause blackouts or sudden deathWhat is the mechanism of tachyarrhythmias seen in Re-entrant circuit?Re-entry requires an area of slow conduction, unidirectional block and two pathways: - Block at slow tract and fast moves down - Slow moves retrograde in fast tract and blocks the incoming next fast - Retrograde fast re-enters in the slow tract - Produces an extra APWhat are examples of re-entrant arrhythmias?Atrial tachycardia, atrial flutter or atrial fibrillation Supra ventricular re-entrant tachycardia (as in Wolff-Parkinson-White syndrome) Ventricular tachycardia (most common)What is the definition of Wolff-Parkinson-White syndrome?Supra ventricular re-entrant tachycardia due to an accessory AV connection/bypass tract (Bundle of Kent)What is the mechanism of Wolff-Parkinson-White syndrome?The accessory AV connection "pre-excites" the ventricle, causing a short PR interval and a relatively wide QRS with a slurred upstroke, termed a DELTA WAVE. If enough times has elapsed, the cardiac impulse can travel retrograde to the atria and initiate a re-entrant supraventricular tachycardia.Identify the difference between WPW-block and Long QT-syndromeHow do you differentiate between a supraventricular tachycardia (SVT) and a ventricular tachycardia (VT)?Look at the QRS complex: - If the QRS is narrow - SVT (w/in 3 boxes) - If the QRS s wide - VTWhat does a narrow QRS complex indicate?Depolarization of the ventricles must be occurring normally, over the specialized conduction tissues and the arrhythmia must be originating at or above the AV node. Seen in Supraventricular Tachycardia.What does a wide QRS complex indicate?Indicates that ventricular depolarization is NOT occurring normally over the specialized conduction tissues. Seen in Ventricular Tachycardia.What are the characteristics of Supraventricular tachycardia?Rhythm - regular Rate - 140-220 bpm QRS duration - normal (narrow) P wave - often buried in preceding T wave P-R interval - depends on site of supraventricular pacemakerWhat is the mechanism of supraventricular tachycardia (SVT)?Impulses stimulating the heart are not being generated by the sinus node, but instead are coming from a collection of tissue around and involving the atrioventricular node.What are some commonly occurring SVTs?Atrial tachycardia (atrial rate: 150-250/min) Atrial flutter (atrial rate: 250-350/min) Atrial fibrillation (atrial rate: > 350/min and multifocal) AV nodal re-entrant tachycardia Atrioventricular re-entrant tachycardiaWhat are the characteristics of Atrial flutter?Rhythm - regular Rate - around 110bpm QRS duration - usually normal P wave - replaced with multiple F waves (flutter waves), at a rate of 2:1 or 3:1 P-R interval - not measurableWhat is the mechanism of an Atrial flutter?As with SVT, the abnormal tissue generating the rapid heart rate is in the atria; the AV node is NOT involved in this case.What is the most common complication of atrial fibrillation?Systemic thromboembolismWhat are the characteristics of Atrial Fibrillation?Rhythm - Irregularly irregular Rate - usually 100-160 bpm, but slower if on medication QRS duration - usually normal P wave - Not distinguishable as the atria are firing off all over P-R interval - not measurableWhat is the mechanism of Atrial fibrillation?Many sites within the atria are generating their own electrical impulses, leading to irregular conduction of impulse to the ventricles that generate the irregular pulse.What are the characteristics of Ventricular Tachycardia (VT)?Rhythm - regular Rate - 180-190bpm QRS duration - prolonged ("wide QRS" - >3 boxes) P wave - not seenWhat is the mechanism of ventricular tachycardia (VT)?Abnormal tissues in the ventricles generating a rapid and irregular heart rhythm. Associated with a poor cardiac output.What are the characteristics of Ventricular Fibrillation (VF)?Rhythm - Irregular Rate - 300+, disorganized QRS duration - not recognizable P wave - not seenWhat is the mechanism of ventricular fibrillation?Disorganized electrical signals cause the ventricles to quiver instead of contract in a rhythmic fashion. Patient become unconscious as there is NO cardiac output. Condition may occur during or after an MI. This is a medical emergency - patient needs to be defibrillated, quickly!What do you look at when assessing an arrhythmia?