Arrhythmias: S-A Nodal and Atrial

1. Arrhythmias: S-A Nodal and Atrial

2. 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

3. 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

4. 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

5. 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

6. 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”

7. 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.

8. 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)

9. 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

10. 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

11. 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

12. 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

13. 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.

14. 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

15. 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

16. 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

17. 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