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
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)
1. 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)
1. Junctional (idiojunctional) or ventricular (idioventricular) rhythm
2. 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
1. Ectopic beats are those that arise outside the sinus node.
2. Extrasystole is an ectopic beat that is both premature and constantly related to
the previous beat.
3. Couplet - the extrasystole together with its preceding parent beat.
4. Coupling interval - the interval between the extrasystole and its parent beat.
(Varies => suggests enhanced automaticity)
5. Fixed coupling - a condition in which the coupling interval is constant for each
successive couplet. (Suggests reentry)
6. Contraction - the mechanical event of myocardial contraction associated with
the heart beat; e.g., PAC & PVC.
7. Beat* - refers to the electrical and mechanical events associated with the
heart beat; e.g., APB & VPB.
8. 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
Atrial Escape Beat
QRS is slightly different but still narrow,
indicating that conduction through the
ventricle is relatively normal
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
PAC
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++ channel blockers, 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++ channel blockers 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
P-R:
QRS:
conduction
ST:
abnormal; recognition may be difficult
Usually not measurable; may be prolonged
Usually normal and married to P ; widened if aberrant
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
Rhythm usually begins
with PAC
Note REGULAR rhythm
in the tachycardia