Cardiac Rhythms Flashcards by Nina Roberts

Sinus node
1- where
2- rate of automaticity

1- upper right atrium

2- 60 to 100 beats/min

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AV node
1- where
2- rate of automaticity

1- low right atrium, near tricuspid valve

2- 40 to 60 beats/min

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AV node primary functions (3 total)

1- slows conduction of impulses from atria to ventricles to allow time for atria to empty/contract
2- acts as backup pacemaker if Sinus node fails
3- protects the ventricles by screening out dangerously rapid atrial impulses

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Bundle of His location

at the bottom of the AV node, leading to R/L bundle branches

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Bundle Branches

Right –> Right ventricle, Left –> Left ventricle (has two devisions: anterior and posterior fascicles)

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Purkinje fibers
1- location
2- rate of automaticity

1- spread out from the bundle branches along the ventricles

2- 20 to 40 beats/min

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P wave
1- what it represents on ECG
2- duration

1- atrial depolarization 2- less than 0.11 second

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QRS complex
1- what it represents on ECG
2- duration

1- ventricular depolarization

2- 0.04 to 0.10 seconds

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T wave 1- what it represents

1- ventricular repolarization

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PR interval 1- what it represents 2- duration

1- time required for the impulse to travel through the atria, AV junction, to the purkinje system
2- 0.12 to 0.20 seconds

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QT interval 1- what it represents 2- duration

1- duration of ventricular depolarization and repolarization
2- Men < 0.45 seconds Women < 0.46 seconds

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ECG graph paper seconds / mV
HORIZONTAL (seconds) 1- small box 2- large box
VERTICAL (millivolts, millimeter) 1-small box 2- large box

HORIZONTAL 1- small box = 0.04 sec 2- large box = 0.20 sec

VERTICAL 1- small box = 0.1 mV (1 mm) 2- large box = 5 mV (5 mm)

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Treatment(s) of SYMPTOMATIC bradycardia (HR<60)

Atropine 0.5mg IV, temporary or permanent pacing, DC potentially responsible medications, minimize vagal stimulation

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Treatment of sinus arrest
(sinus arrest is when more than one sinus impulse in a row fails to form [vs sinus pause- in which only one impulse fails to form])

DC potentially responsible medications, minimize vagal stimulation
IF periods of sinus arrest frequent & cause hemodynamic compromise- Atropine 0.5mg IV, temporary or permanent pacing

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Treatment of atrial tachycardia 
1- acute treatment
--Stable
--Unstable
2- ongoing management

Acute Treatment:
- IV beta-blocker, diltiazem or verapamil if hemodynamically stable
- synchronized cardioversion if hemodynamically unstable
- Adenosine to restore SR or Dx tachycardia
Ongoing Management:
- Catheter ablation
- oral BB’s, diltiazem, verapamil
- flecainide or propafenone
- sotalol or amiodarone

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Treatment of SVT of unknown mechanism

vagal maneuvers
adenosine (6mg rapid IVP, may repeat w/ 12mg if necessary)
synchronized cardioversion
IV verapamil or diltiazem (hemodynamically stable)
IV BB’s (hemodynamically stable)

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Acute Treatment of Atrial Flutter

pharmacological cardioversion w/ PO dofetilide or IV ibutilide
IV or PO BB’s, diltiazem, or verapamil (for rate control if hemodynamically stable)
synchronized cardioversion
IV amiodarone for rate control

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Classifications of A Fib

Paroxysmal: episodes that terminate spontaneously or w/ intervention within 7 days of onset
Persistent: episodes that last more than 7 days
Long-standing persistent: continuous AF lasting > 12 months
Permanent: >23 months & decision made to stop attempts to restore/maintain SR
Recurrent: 2+ more episodes

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CHA(2)DS(2)VASc score (0 - 10)

C = CHF
H = hypertension
A(2) = age> 75 years (2 pts) 
D = diabetes
S(2) = Hx stroke, TIA, thromboembolism (2 pts)
V = vascular disease (prior MI, PAD,  aortic plaque)
A = age 65-74
Sc = sex category female

What does the CHA-DS-VASc score used to assess?

Stroke risk in AF patients; can be used to assess type of anti-thrombotic therapy

Idioventricular rhythm

where it originates
rate
why it may occur

originates- ectopic focus in the ventricles
rate- < 50 beats/min
occurs when the sinus node and junctional tissue fail to fire or fail to conduct impulses to the ventricle

Ventricular tachycardia (VT) classification

duration
morphology

duration
- nonsustained = lasts < 30 seconds
- sustained = lasts > 40 seconds
- incessant = present most of the time
morphology
- monomorphic = QRS have same shape
- polymorphic = QRS have varying shapes
- bidirectional = alternating upright & negative QRS complexes

What is Torsades de pointes (“Twisting of the points”)

polymorphic VT that occurs in the presents of a long QT interval

Treatment of VT (w or w/out a pulse)

Pulse Present:
- Stable: first choice is amiodarone (then, lidocaine or procainamide)
- Unstable: synchronized cardioversion
No Pulse: immediate defibrillation

Second Degree AV Block: Type I ("Wenckebach")

"longer long longer drop" - occurs in the AV node - progressive increase in conduction times until one impulse fails to conduct ("dropped") = PR intervals gradually lengthen until one P wave fails to conduct and is not followed by a QRS, then cycle repeats

Second Degree AV Block: Type II

- occurs below the AV node in the bundle of His or bundle branch system - sudden failure of the conduction of an atrial impulse to the ventricles without progressive increases in conduction time of consecutive P waves - irregular rhythm d/t blocked beats - periodically, a p wave is not followed by a QRS - QRS almost always wide (d/t associated BBB) - more serious than Type I (d/t higher incidence of associated sx's & progression to complete AVB)

Types of temporary pacing

1. Transvenous 2. Epicardial 3. External (Transcutaneous)

How is transvenous pacing done?

by percutaneous puncture of a large vein (IJ, subclavian, AC or femoral) and advancing a pacing lead into the apex of the right ventricle, the lead is attached to an external pulse generator kept on the patient or at bedside

How is epicardial pacing done?

electrodes are placed on the atria or ventricles during cardiac surgery

What are the two components of a cardiac pacing system?

1- pulse generator | 2- pacing leads

What are the two main functions of a pacing system?

capture and sensing

What does capture mean (re: pacing systems)?

capture means that a pacing stimulus results in depolarization of the chamber being paced

What are some possible reasons that capture would NOT occur?

if the distal tip of the pacing lead is not in contact with healthy myocardium capable of responding to the stimulus; pacing in infarcted tissue usually prevents capture; or if the catheter is not in direct contact with myocardium

What does sensing mean (re: pacing systems)?

sensing means that the pacemaker is able to detect the presence of intrinsic cardiac activity

What is asynchronous (fixed-rate) pacing and why can it be dangerous?

when the pacemaker paces at the programmed rate regardless of intrinsic cardiac activity it can result in competition between the pacemaker & the hearts own electrical activity asynchonous pacing in the ventricle is unsafe b/c of the potential for pacing stimuli to fall during repolarization & cause VF

What does demand mean (re: pacing systems)?

Demand means that the pacemaker paces only when the heart fails to depolarize on it own In demand mode, the pacemaker's sensing circuit is capable of sensing intrinsic cardiac activity & inhibiting pacer output when intrinsic activity is present

How do you confirm capture with external (transcutaneous) pacing?

the presence of a pulse with every pacing spike confirms ventricular capture

How does one measure the QTc?

- using the Bazett formula | - measured QT interval DIVIDED BY the sqaure root of the R-R interval

Best leads for monitoring wide QRS rhythms?

V1 and V6 (or their bipolar substitutes- MCL1 and MCL6)

PAC (premature atrial contraction) defining features:

- narrow QRS - upright P wave - different morphology?

PJC (premature junction contraction) defining features:

- narrow QRS | - absent/inverted P wave

PVC (premature ventricular contraction) defining features:

- wide QRS - absent P wave - T wave opposite R wave

SVT (supraventricular tachycardia) defining features:

- HR > 150 - narrow QRS - indistinguishable P wave (P or T wave?) - regular rhythm

Junctional Rhythm defining features:

- HR 40-60 - narrow QRS - absent/inverted P wave

Bundle Branch Blocks R BBB V1 QRS Morphology characteristic? L BBB V1 QRS Morphology characteristic?

R BBB: "rabbit ears" or "M" pattern; QRS points up (like a R turn signal) L BBB: deep wife WRS "W" pattern; QRS points down (like a L turn signal)

What is the importance of axis deviation? | What is the normal degrees of axis deviation?

wave of depolarization shifts AWAY from infarct and TOWARD area of hypertrophy -30 to +90

Normal Axis Deviation QRS: Lead 1 (+) AVF (+) Look at lead 1 and AVF (is the QRS positive or negative) R axis deviation 1: __ AVF: __ L axis deviation 1: __ AVF: __

R axis deviation 1: (-) AVF: (+) | L axis deviation: 1: (+) AVF: (-)