Cardiac Conduction Problems Part 1 Flashcards
Arrhythmias
- Disorders of Electrical impulses or conduction within the heart
- Can cause disturbances of the HR, heart rhythms or both
- Can cause changes in hemodynamics due to changes in pumping action
- Diagnosed by ECG
- Treatment is based on the frequency and severity of symptoms produced
- Named according to site of origin of the electrical impulse and mechanism of conduction involved.
- For example if impulse originates in SA (Sinoatrial node) node, and the rate is above 100 its Sinus Tachycardia
- Conduction should start in the SA node but heart blocks and arrythmias can interupt that
- If the conduction starts in SA node its sinus
Normal electrical flow through the heart
- SA
- AV
- Bundle of his
- Bundle branch
Main pacemaker of the heart
SA node,with a normal electrical stimulus of 60-100 impulses per min
Stimulation of the sympathetic nervous system results in
- Positive Chronotropy
- Positive dromotropy
- Positive inotropy
- Constriction of peripheral blood vessels which increase BP
Stimulation of the parasympathetic nervous system
- reduces HR, AV conduction, and force of atrial contraction
- Reduction of BP
Diagnostic workup of cardiac arrhythmias, to identify cause vs problems with the heart itself
- ECG and echo
- Labs with chemistries (K, Mg, Ca, Na) and BNP (HF), thyroid function test, CBC
- Dig levels if appropriate
- Cardiac enzymes if MI (Troponin)
- CT and MRI and D-dimer if PE suspected
- Chest X-ray
- Exercise testing; holter monitoring
- Electrophysiology studies
- Cardiac cath
Electrophysiology studies
Setting the pt into the rhythm to see how they act or see cause
Why echo for arrythmias
Echo can see EF and reduced EF can lead to arrhythmias
P wave
Atrial depolarization
PR interval
- Start of P wave (Atrial depolarization) to the start of ventricular depolarization (Start of Q wave)
- the PR segment is the end of the P wave to the start of the Q wave
Normal is 0.12-0.2 sec 3-5 boxes
Find a p wave that starts on a line
QRS complex
Ventricular depolarization
Normal is 0.8-0.12 seconds, 2-3 boxes
T wave
Ventricular relaxation (repolarization)
QT interval
- Start of Q wave to end of T wave
- Drugs can prolong this (antidepressants and such)
How long is one small box, ECG (1mm)
0.04 seconds
How long is a large box, ECG (5mm)
0.2 seconds
How do you calculate the HR using an ECG
- Count the QRS complex (Only regular rhythms)
- Most strips are a standard 6 seconds, so multiple the number by 10
- Easy but not accurate
Normal is 60-100
Calculating the rhythm
- Determine if it is regular or irregular
- Measure from R wave to R wave
- If irregular is there any pattern to irregularity
- Is there a P wave for each QRS (Very important for heart blocks and arrythmias)
- For heart blocks check the pr ratio
Calculating the rhythm: P wave
- There should be one P wave for each QRS (Is there more than one)
- Are the P waves rounded?, are they notched or peaked? (Each P wave should look the same)
- All P waves should look essentially the same in size shape and direction to be considered normal
Sinus bradycardia
- Same as normal sinus but HR is under 60 bpm
- Normal when sleeping or athletes
- Persistent brady can cause decreased CO
Causes of sinus brady
- Valsalva maneuver
- Vagal stimulation
- Sleep apnea
- Hyperkalemia
- Hypoglycemia
- Increased intracranial pressure
- Disease of SA node
- Admin of drugs (Dig, CCB, BB)
Treatment of sinus brady
- None
- If symptomatic however you give Atropine, temp or perm pacemaker, Treat the cause
Sinus Tachycardia
- Same as Normal sinus but over 100 bpm
- Normal after exercise
- Can lead to decreased CO and decreased BP due to there not being enough time for the heart to fill with blood
Causes of sinus tachy
- Fever
- Pain
- Hypoxia
- PE
- HF
- Hypovolemia/hypotension
- Stress
- Anxiety
- Drugs that increase sympathetic tone (Epi, NE, DA, Dobutamine, isoprotenrenol, nitroprusside
Treatment of sinus tachy
Treat the cause
Overview of sinus arrhythmias
- All are regular
- All have a P wave for a QRS complex
- QRS with is the same for all
- PR intervals are within normal limits
- Rates are the main thing differing
Sinus arrhythmias (normal one)
- Time between beats can be slightly shorter or longer depending on whether youre breathing in or out
- HR increases when breathing in
- HR slows when exhaling
Considered normal
How much does the Atria contribute to CO
25-30% with the atrial kick, with arrhythmias this will significantly decrease CO
Atrial arrhythmias
- Ectopic sites on the atrium, that generate an impulse, some are blocked at the AV node some are not
- A-fib, a-flutter, SVT
- SA to av node transmission is impaired
A-fib
- Irregular Heart rhythm originating from an ectopic site in the atria, usually rapid when it first occurs
- Atrium depolarizing at a rate greater than 400 bpm, with the majority of impulses being blocked at the AV node
- AV node conducts impulses irregularly and randomly leading to an irregular ventricular rhythm
- As a result of 400 bpm the atria does not beat but quivers like a. bag of worms
- Very common
- causes loss of atrial kick, decreasing CO
- Blood clots are super common due to pooling of the blood in the atria
Causes of A-fib
- Strongly associated with diseases (HF, CAD, Valve disease, pulmonary disease, DM, HTN) Common after cardiac surgery as well
- Sometimes previpitated by exertion, sleep, caffine and alc
Rapid ventricular rate A-fib
- HR exceeding 100 in a-fib
- Increases myocardial oxygen demands, increases cardiac workload, decreases cardiac output
Treatment of afib: Control of clots
- Anticoagulants: Prevent clot formation due to high risk of stroke with A-fib
- Dabigatran, Ravaroxaban Apixaban warfarin
- Lovenox and heparin
- Stroke risk assessment (CHA2DS2-VASc score)
Super duper important
Treatment of afib: Control of rate
- Beta blockers
- Calcium channel blockers diltiazem (Cardizem)
- Dig
Rapid afib is dangerous
Treatment of afib: Tachybrady syndrome
- HR flips between Tachycardia and bradycardia, so if you give a BB for example it might crash their HR
- Needs a pacemaker to place a perm rhythm that prevents brady
Treatment of afib: Rhythm control
- Cardioversion (Electrical shock and conversion to sinus)
- Meds (Flecainide, Propafenone, Dofetilide, Sotalol (First line agents)) Amiodarone
- Ablation: Radiofrequency cath based, MAZE procedure during CABG
Ablation for A-fib
- Cath is inserted into the heart from femoral area, up onto where the arrhythmia is coming from,
- Area of concern is identified and is burnt or frozen to damage the affected area
- Once completed the cath is removed and incision is closed
- Takes 4 hours
A-Fib and stroke
- Huge risk for a-fib, due to pooling of blood in the aria, left atrial appendage
A-fib on ECG
- Irregularly irregular
- Atrial rate of 400-600, not measurable
- PR, not able to determine (No P wave)
- No P wave only fibrillary waves
- QRS is normal (Its above the bundle of HIS)
- Ventricular rate is normal or fast
Atrial flutter
- Similar to a fib, except its a sawtooth pattern except fib
- A flutter originates in an ectopic site in the atria
- Atrium depolarizes at a rate of 250-400 bpm
- AV node blocks at least half the impulses to the ventricles
More of an electrical issue than a cardiac issue, unlike a-fib
A flutter: Conduction ratio stays the same
ventricular Rhythm will be regular
A flutter: conduction ratio varies
Ventricular rate will be irregular
T/F A flutter is a chronic condition
False, it is uncommon for it to be chronic but not impossible. Usually it converts to A fib or sinus (Spontaneously or following treatment)
Atrial flutter on ECG
- Atrial rate of 250-400 (can count if slow)
- Abnormal P waves (Sawtooth/flutter waves)
- PR unable to determine (Too many P waves)
- Rhythm may be regular or irregular
- Varying degree of flutter waves can be measured per QRS complex (2:1, 3:1 …)
- Treatment is the same as A-fib
How does A-fib differ from A-flutter: Cause
A-fib is caused more often from cardiovascular issues such as IHD, HTN, high cholesterol , nicotine, DM
A flutter is less common and usually due secondary to an abhorrent electrical pathway in the atria
Paroxysmal A-fib
- A-fib that occurs intermittently and stops spontaneously within 7 days
- Dangerous because of risk of shooting a clot to the brain when it resolves
Persistent A-fib
- Last longer than 7 days
- May require cardioversion to restore sinus rhythm
Long standing A-fib
- Similar to persistent but last longer than a year
Paroxysmal or Supraventricular Tachycardia (PAT/SVT)
- Originates due to an ectopic pacemaker site in the atria
- Atrial rate of 140-150
- May start and stop abruptly
- Continuous rhythm or short burst of SVT
- Rapid ventricular rate, decreased ventricular filling
Is SVT a ventricular or atrial arrythmia
Atrial
Clinical manifestations of SVT
- Palpitations
- Fatigue
- Exercise intolerance
- mild dyspnea
Causes of SVT
- CAD or mitral valve disease
- Nicotine
- Stress/anxiety
- Caffeine/alc
- Fatigue
- Lung disease (COPD)
- Hyperthyroidism
- Dig tox
- More common in women
Mgmt of SVT
- Vagal maneuvers: (try and poop your pants), coughing, holding breath, carotid massage (not really)
- Adenosine IV (Drug of choice)
- Calcium channel blockers (Cardizem), BB
- Pacemaker
- Cardioversion
- Ablation
SVT on an ECG
- HR is 150-250 bpm
- Rhythm is usually regular
- P waves are hidden in T waves, the TP wave is distinguishing feature of this rhythm
- PR is non existent
- QRS is narrow (fast)
Adenosine
- Given IV
- 6mg dose followed by 20 mg saline slammed
- Stops heart temp but it should start back up
Prolonged QT interval
- Delayed repolarization of the myocardium
- Normal QT interval is <440 msec
- Can progress to ventricular arrhythmias, (Torsades de pointes)
- mgmt is Mg
Causes of prolonged QT interval
- Lots o drugs
- Hypokalemia
- Hypomag
- Certain arrhythmias
- Stroke
- HF
