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Arrhythmias: S-A Nodal and Atrial - PowerPoint PPT Presentation

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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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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

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

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

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

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”

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.

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)

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

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


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

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

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.

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

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

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

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