Electrocardiography and rhythm disorders Flashcards
What can an ECG be used for?
Can be used to detect:
- Conduction abnormalities
- Structural abnormalities
- Perfusion abnormalities
What are the advantages of an ECG?
Relatively cheap and easy to undertake
Reproducible between people & centres (procedure is internationally standardised irrespective of who conducts it- decreases subjectivity in diagnostics)
Quick turnaround on results/ report (no specialist interpretation is needed)
What are electrodes?
“sticky bits”
- The interface b/t the body and the electricity coursing through the sensor
What are cables/ wires?
Communicate from the electrodes to the device
What are the “leads”?
“lines on the paper”
there are 12 leads- views of the heart represented by those lines on the ECG
What is a vector?
Cardiac vectors are what we’re measuring on the ECG trace
A defibrillater is used if a patient is asystolic (“flat-lines”) and needs their electrical activity restored, true or false?
False: When a patient is asystolic- they have “non-shockable rhythm”
- There is no electrical activity
- So the defibrillator will not issue a shock
- Administer adrenaline instead
What is “sinus rhythm”?
Each P-wave is followed by a QRS wave (1:1)
Rate is regular (even R-R intervals) and normal (83 bpm) [gap between each complex is the same]
Otherwise unremarkable
What is “Sinus bradycardia”?
- Each P-wave is followed by a QRS wave (1:1) [so it is still a sinus rhythm- generated by the sinoatrial node]
- Rate is regular (even R-R intervals) and slow (56 bpm)
- distance between rhythm is prolonged
- Can be healthy, caused by medication or vagal stimulation; you need to understand the patient/ context
What is “sinus tachycardia”?
- Each P-wave is followed by a QRS wave (1:1)
- Rate is regular (even R-R intervals) and fast (107 bpm)
- distance between the rhythm is shortened
- Often a physiological response (i.e. secondary) e.g. excitation of the SNS or response to medication
What is “sinus arrhythmia”?
- Each P-wave is followed by a QRS wave; still sinus generated
- Rate is irregular (variable R-R intervals) and normal-ish (65-100 bpm)
- R-R interval varies with breathing cycle:
- Usually the SAN wants to depolarise at 110 bpm but now it is depolarising at 70 bpm
- The parasympathetic NS slows it down via the vagus nerve (the PNS can slow/ speed it up depending on what stage of breathing we’re at)
How do the waves change on an ECG between expiration and inspiration?
Expiration:
- lower HR
- longer R-R interval
- there is no innervation of the respiratory musculature; during this, the PNS slows down the SAN/ electrical conduction
Inspiration:
- Higher HR
- Shortened R-R interval
- During inspiration the PNS allows the SAN to send the signals (not slowed down)
How can you calculate Heart rate from an ECG?
300/ x
x= number of large squares on the ECG paper
What is “Atrial fibrillation”?
- Problems that originate above the AV node
- Oscillating baseline – atria contracting asynchronously
- Muscle is not really contracting; NO P WAVES
- but everything in the ventricles are working; QRS COMPLEX IS NORMAL
- Rhythm can be irregular and rate may be slow: AVN generates the rhythm; if AVN is lost, HR slows down= increased risk of clot formation
- Turbulent flow pattern increases clot risk
- Atria not essential for cardiac cycle: gravity (blood pressure) does the work of getting the blood to the ventricles (contractions are just more efficient)
What is “Atrial flutter”?
- Regular saw-tooth pattern in baseline (II, III, aVF):
- there are lots of P waves
- but not every P wave is followed by a QRS complex
- P waves are too fast (can not relax and depolarise again)
- Atrial to ventricular beats at a 2:1 ratio, 3:1 ratio or higher
- Saw-tooth not always visible in all leads
What is “First degree heart attack”?
- Prolonged PR segment/interval caused by slower AV conduction
- Regular rhythm: 1:1 ratio of P-waves to QRS complexes (every P results in a QRS complex)
- Most benign heart block, but a progressive disease of ageing
What is “second degree heart block (Mobitz I)”
- Gradual prolongation of the PR interval until beat skipped (beat skipped as there is no conduction through the AV node)
- Most P-waves followed by QRS; but some P-waves are not
- Regularly irregular: caused by a diseased AV node (where we have conduction= the R-R intervals are regular, where we don’t have conduction= extended period of time without an R wave)
- Also called Wenckebach
What is “second degree heart block (Mobitz II)?
- P-waves are regular, but only some are followed by QRS
- No P-R prolongation (The P-R interval, when you see it, is consistent/ normal length)
- Regularly irregular: successes to failures (e.g. 2:1) or random
- Can rapidly deteriorate into third degree heart block (absolutely no communication b/t P and R waves)
What is “Third degree (complete) heart block”?
- Complete dissociation b/t the P waves and the R waves
- P-waves are regular, QRS are regular, but no relationship (P-P waves are regularly spaced, R-R waves are regularly spaced, but they are not paced at the same rate)
- P waves can be hidden within bigger vectors
- A truly non-sinus rhythm (the rhythm of the ventricles pumping is caused by the ventricles themselves) – back-up pacemaker in action when the SAN/ AVN fail, the ventricles are able to create the electrical signal required for mechanical contraction
What is “ventricular tachycardia”?
- P-waves hidden (difficult to spot)– dissociated atrial rhythm: the rhythm the ventricles create is causing the P waves to be obscured by these much higher vectors; the P waves are atrial muscle, not very thick, but the QRS complex is ventricles, much thicker
- Rate is regular and fast (100-200 bpm)
- At high risk of deteriorating into fibrillation (cardiac arrest
- Shockable rhythm – defibrillators widely available
What is ventricular fibrillation?
- Heart rate irregular and 250 bpm and above
- Heart unable to generate an output: signals are irregular
- Shockable rhythm – defibrillators widely available
- NOTE: it is not about the ventricles ‘beating too fast’ but they’re not contracting in a coordinated manner
What is “ST elevation”?
- P waves visible and always followed by QRS (1:1)
- Rhythm is regular and rate is normal (85 bpm)
- ST-segment is elevated >2mm above the isoelectric line
- Caused by infarction (tissue death caused by hypoperfusion)
What is “ST depression”?
- P waves visible and always followed by QRS
- Rhythm is regular and rate is normal (95 bpm)
- ST-segment is depressed >2mm below the isoelectric line
- Caused by myocardial ischaemia, not caused by tissue damage (coronary insufficiency)
