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Arrhythmias: S-A Nodal and Atrial. Rhythms from the Sinus Node. Normal Sinus Rhythm (NSR). Sinus Tachycardia: HR > 100 bpm Causes: Withdrawal of vagul tone & Sympathetic stimulation ( exercise , fight or flight) Fever & inflammation

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Arrhythmias: S-A Nodal and Atrial

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Arrhythmias s a nodal and atrial

Arrhythmias:

S-A Nodal and Atrial


Arrhythmias s a nodal and atrial

Rhythms from the Sinus Node

Normal Sinus Rhythm (NSR)

  • Sinus Tachycardia: HR > 100 bpm

    • Causes:

      • Withdrawal of vagul tone & Sympathetic stimulation (exercise, fight or flight)

      • Fever & inflammation

      • Heart Failure or Cardiogenic Shock (both represent hypoperfusion states)

      • Heart Attack (myocardial infarction or extension of infarction)

      • Drugs (alcohol, nicotine, caffeine)

  • Sinus Bradycardia: HR < 60 bpm

    • Causes:

      • Increased vagal tone, decreased sympathetic output, (endurance training)

      • Hypothyroidism

      • Heart Attack (common in inferior wall infarction)

      • Vasovagul syncope (people passing out when they get their blood drawn)

      • Depression


Arrhythmias s a nodal and atrial

Rhythms from the Sinus Node

  • Sinus Arrhythmia: Variation in HR by more than .16 seconds

    • Mechanism:

      • Sinus node forms impulse irregularly

      • Most often: changes in vagal tone associated with respiratory reflexes

      • Benign variant

    • Causes

      • Most often: youth and endurance training


Arrhythmias s a nodal and atrial

Rhythms from the Sinus Node

  • SA Block or Sinus Exit Block (Huff, 4th ed., strip 6-6, 20, 27; Conover p 52)

  • Failure of sinus impulse to exit SA (conduction failure) or failure of impulse to activate atria (inadequate stimulus)

  • Characteristics- entire PQRST complex absent for one or more cycles - recognized by groups of sinus conducted beats followed by pauses without P's

  • Type I (Wenckebach); rate bradycardia due to pause, normal P-waves, group beating, shortening P-P intervals, and pauses < 2 times short cycle

  • Type II; dropped P-waves with fixed P-P intervals and pauses that are multiples of uninterrupted sinus cycles


Arrhythmias s a nodal and atrial

Rhythms from the Sinus Node

  • Sinus Arrest or Sinus Pause (Huff, 4th ed., strip 6-15, 24; Conover p 55)

  • failure of sinus node to form impulse

  • (1)problem with impulse formation (decreased automaticity)

  • (2)P-P interval disturbed, pause cycle no numeric relationship to basic cycle length

  • (3)may be atrial, junctional or ventricular escape

  • Other terminology: Partial (incomplete) - rhythm with long pause and occasional absence of PQRST. Complete (sinus arrest, sinus standstill, atrial paralysis, atrial standstill) (Huff, 3rd ed., strip 6-9, 24, 30)

  • Junctional (idiojunctional) or ventricular (idioventricular) rhythm

  • Asystole and death


Arrhythmias s a nodal and atrial

Rhythms from the Sinus Node

  • Sick Sinus Syndrome: Failure of the heart’s pacemaking capabilities

    • Causes:

      • Idiopathic (no cause can be found)

      • Cardiomyopathy (disease and malformation of the cardiac muscle)

    • Implications and Associations

      • Associated with Tachycardia / Bradycardia arrhythmias

      • Is often followed by an ectopic “escape beat” or an ectopic “rhythm”


Arrhythmias s a nodal and atrial

Atrial Rhythms Pacemaker NOT S-A, but R or L atrium

  • Definitions

  • Ectopic beats are those that arise outside the sinus node.

  • Extrasystole is an ectopic beat that is both premature and constantly related to the previous beat.

  • Couplet - the extrasystole together with its preceding parent beat.

  • Coupling interval - the interval between the extrasystole and its parent beat. (Varies => suggests enhanced automaticity)

  • Fixed coupling - a condition in which the coupling interval is constant for each successive couplet. (Suggests reentry)

  • Contraction - the mechanical event of myocardial contraction associated with the heart beat; e.g., PAC & PVC.

  • Beat* - refers to the electrical and mechanical events associated with the heart beat; e.g., APB & VPB.

  • Compensatory pause - refers to the cycle following the premature beat; pause 'compensates' for prematurity of extrasystole and sinus rhythm resumes on schedule.


Arrhythmias s a nodal and atrial

Atrial Rhythms

Definitions (continued)

Fully compensatory pause - the interval from the normal beat preceding the extrasystole to the normal beat following the extrasystole equals two normal sinus cycles. (Huff, 4th ed, pg 193, figure 9-5)

(a) Measurement of interval from R preceding to R following ectopic = 2 * R-R

Less than compensatory (noncompensatory) pause - measurement from R preceding to R following ectopic < 2 * R-R (Huff 4th ed, pg 96, fig 7-8)


Arrhythmias s a nodal and atrial

Atrial Rhythms

QRS is slightly different but still narrow,

indicating that conduction through the

ventricle is relatively normal

Atrial Escape Beat

normal ("sinus") beats

sinus node doesn't fire leading to a period of asystole (sick sinus syndrome)

p-wave has different shape indicating it did not originate in the sinus node, but somewhere in the atria. It is therefore called an "atrial" beat


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • Premature Atrial Contractions (PACs): (Huff, 4th ed., strip 7-3, 5, 7)

  • An ectopic focus in the atria discharges causing an early beat

  • The P-wave of the PAC will not look like a normal sinus P-wave (different morphology)

  • QRS is narrow and normal looking because ventricular depolarization is normal

  • PACs may not activate the myocardium if it is still refractory (non-conducted PACs – pause)

  • PACs may be benign: caused by stress, alcohol, caffeine, and tobacco

  • PACs may also be caused by ischemia, acute MI’s, d electrolytes, atrial hypertrophy

  • PACs may also precede PSVT

  • Post-extrasystolic interval usually less than compensatory; sinus node reset

Non conducted PAC

Non conducted PAC distorting a T-wave

PAC


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • PAC with Aberrant Ventricular Conduction): (Huff, pg 96, fig 7-7)

  • PAC finds one bundle branch refractory => wide beat with R or L bundle branch morphology

    • PAC or PVC??

      • P’ & less than compensatory pause favors PAC


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • Wandering Atrial Pacemaker: (Huff, pg 92, fig 7-3, strip 7-4)

  • Various foci in atrium - SA and ectopics

  • Summary

  • Rate:usually normal (60-100)

  • Rhythm:slightly irregular due to variation in pacemaker site

  • P wave:P or P varies in shape due to changing pacemaker site

  • P-R:varies depending on pacemaker site

  • QRS:usually normal


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • Atrial Fibrillation (A-Fib): (Handouts & Huff 4th ed, strip 7-1, 10)

  • Multiple ectopic reentrant focuses fire in the atria causing a chaotic baseline, rate 400 ± 50

  • The rhythm is irregular and rapid (approx. 140 – 150 beats per minute)

  • Q is usually d by 10% to 20% (no atrial “kick” to ventricular filling)

  • May be seen in CAD (especially following surgery), mitral valve stenosis, LV hypertrophy, CHF

  • Treatment: DC cardioversion & O2 if patient is unstable

    • drugs: (rate control) b & Ca++ channelblockers, digitalis, to d AV Conduction

    • amiodarone to d AV conduction + prolong myocardial AP (u refractoriness of myocardium)

  • The danger of thromboembolic events are enhanced due to d flow in left atrial appendage

    • Treatment: anticoagulant drugs (Warfarin / Coumadin)

      • International Normalized Ratio (INR – normalized PT time) should be between 2 and 3.


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • Atrial Flutter: (Handouts & Huff 4th ed, strip 7-8, 12)

  • A single ectopic macroreentrant focuses fire in the atria causing the “fluttering” baseline

  • AV node cannot transmit all impulses (atrial rate: 250 –350 per minute)

    • ventricular rhythm may be regular or irregular and range from 150 –170 beats / minute

  • Q may d, especially at high ventricular rates

  • A-fib and A-flutter rhythm may alternate – these rhythms may also alternate with SVT’s

  • May be seen in CAD (especially following surgery), VHD, history of hypertension, LVH, CHF

  • Treatment: DC cardioversion if patient is unstable

    • drugs: (goal: rate control) Ca++ channelblockers to d AV conduction

    • amiodarone to d AV conduction + prolong myocardial AP (u refractoriness of myocardium)

  • The danger of thromboembolic events is also high in A-flutter


Arrhythmias s a nodal and atrial

Atrial Rhythms

Atrial Tachycardia: subtype of Supraventricular Tachycardia

1.differentiated from sinus tach

2.Summary

Rate:Atrial: tachycardia 140-250 (200±50)

Ventricular: usually 1:1 conduction, slower with A-V block

Rhythm: Usually regular; may vary (e.g., paroxysmal)

P wave: P abnormal; recognition may be difficult

P-R:Usually not measurable; may be prolonged

QRS:Usually normal and married to P; widened if aberrant conduction

ST:Depression frequently seen

3. may occur with (CAD, mitral valve disease, WPW) and without HD

4.mechanisms (2 types)

a.ectopic focus in atrium

b.reentry at AV or HIS - major cause of PAT & SVT


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • Multifocal Atrial Tachycardia (MAT):

  • Multiple ectopic focuses fire in the atria, all of which are conducted normally to the ventricles

    • QRS complexes are almost identical to the sinus beats

  • Rate is usually between 100 and 200 beats per minute

  • The rhythm is always IRREGULAR

  • P-waves of different morphologies (shapes) may be seen if the rhythm is slow

    • If the rate < 100 bpm, the rhythm may be referred to as “wandering pacemaker”

  • Commonly seen in pulmonary disease, acute cardiorespiratory problems, and CHF

  • Treatments: Ca++ channel blockers, b blockers, potassium, magnesium, supportive therapy for underlying causes mentioned above (antiarrhythmic drugs are often ineffective)

Note different P-wave morphologies when the tachycardia begins

Note IRREGULAR rhythm in the tachycardia


Arrhythmias s a nodal and atrial

Atrial Rhythms

  • Paroxysmal Supraventricular Tachycardia (PSVT): (Huff 4th ed, strip 7-2, 15)

  • A single reentrant ectopic focuses fires in and around the AV node, all of which are conducted normally to the ventricles (usually initiated by a PAC)

    • QRS complexes are almost identical to the sinus beats

  • Rate is usually between 150 and 250 beats per minute

  • The rhythm is always REGULAR

  • Possible symptoms: palpitations, angina, anxiety, polyuruia, syncope (d Q)

  • Prolonged runs of PSVT may result in atrial fibrillation or atrial flutter

  • May be terminated by carotid massage

    • u carotid pressure r u baroreceptor firing rate r u vagal tone r d AV conduction

  • Treatment: ablation of focus, Adenosine (d AV conduction), Ca++ Channel blockers

Note REGULAR rhythm in the tachycardia

Rhythm usually begins with PAC


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