ECG: Tachycardia Flashcards
A patient has tachycardia with a narrow QRS complex. Rhythm is irregular. What are your differentials?
- Atrial fibrillation,
- multifocal atrial tachycardia
- atrial flutter with variable conduction
A patient has tachycardia with a narrow QRS complex. Rhythm is regular. What are your differentials?
- atrial flutter,
- sinus tachycardia,
- AVNRT, AVRT
- atrial tachycardia
A patient has tachycardia with a broad QRS complex. Rhythm is regular. What are your differentials?
- Ventricular tachycardia
- Supraventricular tachycardia with abberancy e.g. WPW or BBB
- SVT with pre-excitation
- antidromic avrt
- pre excited SVT
A patient has tachycardia with a broad QRS complex. Rhythm is irregular. What are your differentials?
- atrial fibrillation with abberancy
- pre- excited AF
- atrial flutter with aberrancy and variable conduction
- polymorphic vt
What are pathological causes of sinus tachycardia?
Pathological causes: congestive cardiac failure, severe lung disease, sepsis, hyperthyroidism, pulmonary embolism
How does junctional escape rhythm present?
- When AV Node becomes the pacemaker! W/ regular rate of 40-60bpm
- Narrow QRS complexes
- No relationship between the QRS complexes and any preceding atrial activity (e.g. P-waves, flutter waves, fibrillatory waves)
P waves may be present / absent; if present:
- Can appear before, during, or after QRS
- Are usually inverted (retrograde) in inferior leads, and +ve in aVR, V1
How does premature atrial contraction (PAC) present?
P wave of premature beat is different from sinus P in Morphology & axis
- The abnormal P wave may be hidden in the preceding T wave 🡪 “peaked” or “camel hump” appearance
- PACS arising close to the AV node activate the atria retrogradely, producing an inverted P wave with a relatively short PR interval ≥ 120 ms
Regular rhythm
Timing – P wave comes too early
A non (fully) compensatory pause
What is the morphology of premature junctional contraction?
- Originates near AV node hence absent or retrograde P wave
- A (fully) compensatory pause
What are the symptoms of paroxysmal supraventricular tachycardia?
palpitations, dyspnoea, dizziness, syncope
What are the triggers of paroxysmal supraventricular tachycardia?
A Fib, PAC
What are the relieving factors of paroxysmal supraventricular tachycardia?
increased vagal tone from Carotid Massage / Valsava helps ABORT
Management
What are the characteristics of AVNRT on ECG?
• Narrow QRS complex
• HR 130-250/min
• Wide QRS Complex AVNRT possible if there is a pre existing BBB / rate aberrant conduction
• Atrial conduction occurs retrogradely producing inverted P waves in inferior leads (II, III, aVF)
• Atrial and ventricular depolarisation occur simultaneously – P waves frequently buried in QRS complex
• P wave may ‘distort’ last part of QRS complex
- Pseudo S wave in inferior leads
•- Pseudo R wave in V1
• Can try vagal manoeuvres first, after which can try adenosine 6,12,12mg
What are the characteristics of pre-excitation AVRT on ECG?
- short PR interval
- PR segment cannot be seen in some cases
What are the characteristics of orthodromic AVRT on ECG?
Anterograde conduction through AV node
- Narrow complex QRS tachycardia due to fast conduction via bundle of His
- There is no more upstroke because the accessory bundle will always be in refractory
- Retrograde P waves after QRS
What are the characteristics of antidromic AVRT on ECG?
Retrograde conduction through AV node
- There is wide complex QRS tachycardia because the ventricles are depolarised via excitation that reaches via the accessory bundle
- P waves RARELY seen (because of widened QRS 🡪 P waves tend to be buried within T waves)
What is the morphology of WPW with A fib?
• Atrial fibrillation can occur in up to 20% of patients with WPW
• Accessory pathway allows for rapid conduction directly to ventricles bypassing the AV node
• Rapid ventricular rates may result in degeneration to VT or VF
• Rate > 200 bpm
• Irregular rhythm
• Wide QRS complexes due to abnormal ventricular depolarisation via
accessory pathway
• Axis remains stable unlike Polymorphic VT
What is the management of WPW with A fib?
- AV node is rate-limited, hence despite hundreds of bpm of atria in A Fib, ventricles depolarise at a max of 200bpm
- In pt w BOK & A Fib, direct depolarisation of ventricles in can lead to Ventricular Fibrillation -> SUDDEN CARDIAC DEATH!
- HOWEVER, in most of these pts majority of A Fib impulses travel thru AV node instead! Hence does not lead to Sudden Cardiac Death!
- However, we CANNOT give AV nodal blocking agent to treat A Fib in these pt -> will force signal down BOK -> V Fib -> death
- Hence, BB, CCB, Amiodarone and Digoxin are C/I
- Instead, we opt to use Procainamide which selectively blocks the accessory pathway conduction
What are the features of atrial flutter on ecg?
- Narrow complex tachycardia
- Regular atrial activity (≈300bpm)
- Loss of isoelectric baseline
- Flutter waves (saw-tooth pattern) best seen in leads II, III, AVF
- Saw-tooth waves have a fast upslope and slow downslope
- Fixed (e.g. 2:1, 3:1) or variable AV blocks
Variations
- May have variable block resulting in irregular rhythm mimicking AF
- 1:1 conduction may occur in sympathetic stimulation or in WPW
Most common: counter-clockwise –> Flutter waves negative in leads II, III, aVF and positive in V1
What is the management of atrial flutter?
Carotid massage may increase degree of block (e.g. 2:1 to 4:1), making it easier to visualize
Treatment
- Hemodynamically unstable – electrical cardioversion
- Rate control (beta blocker, CCB)
- Rhythm control (amiodarone)
- Anticoagulation
- Cavotricuspid isthmus ablation
What are the features of atrial fibrillation on ecg?
- Irregularly irregular rhythm
- Chronic, fibrillatory waves
- No P waves (atrial rate 350-500)
- Absence of an isoelectric baseline
- Variable ventricular rate
- Complications of AF include hemodynamic instability, cardiomyopathy, cardiac failure, and embolic events
What are the causes of atrial fibrillation?
Common
- cardiac: advanced age, hypertension (most common), ischaemic heart disease, valvular heart disease, heart failure
- non cardiac: thyrotoxicosis, sepsis/ acute stress, electrolyte disturbances
Less common
- cardiac: myocarditis/ pericarditis, post cardiac surgery
- non cardiac: obstructive sleep apnea COPD with cor pulmonale, drugs (theophylline/ illicit drugs, long term amiodarone)
What is the management of atrial fibrillation?
Investigate: 2D echocardiogram
Rate control – Target <110bpm
- Amiodarone: Mainly rhythm control; but also slows down rate. May be used in acute setting if you don’t know if there is structural heart disease or not
- Beta blocker 🡪 1st line (especially for patients with HF)
- Calcium channel blockers (non-dihydropyridines) if beta blockers contraindicated
- Digoxin (hardly used)
Rhythm control
- Management dependent on patient profile, symptoms
- Pharmacological: Class IC, III agents
- Electrical cardioversion
Anticoagulation
- CHADSVASC2 score ≥2 & HASBLED score
- Warfarin vs NOACs (Dabigatran, rivaroxaban, apixaban)
What is the ecg findings found in multifocal atrial tachycardia?
- Heart rate usually 100-150bpm
- Irregularly irregular rhythm with varying PP, PR and RR intervals
- At least 3 distinct P wave morphologies in same lead
- Isoelectric baseline between P waves (i.e. no flutter waves)
- Absence of single dominant pacemaker (i.e. not sinus rhythm with frequent PACs)
- Usually occurs in patients with underlying respiratory failure (e.g. COPD exacerbation, decompensated heart failure)
What is the ecg findings found in paroxysmal atrial tachycardia?
Single foci: either enhanced automaticity or re-entrant circuit
Regular, Rate 100-200 bpm
Each QRS preceded by abnormal P wave (upright in V1, negative in II, III, AVF)
May be difficult to differentiate from PSVT; but look for:
- Warm up (irregular period) & cool down (termination) period in automatic form
- Carotid massage no effect in PAT
What are the ecg features of torsades de pointes
- Specific form of polymorphic VT
- Characteristic morphology: QRS complexes “twist” around isoelectric line
- Occurs in context of QT prolongation
- Usually initiated by a VPB starting at the peak of a prolonged T-U wave (“R on T” phenomenon)
What are the features of WPW syndrome?
- PR interval <120ms
- Delta wave – slurring slow rise of initial portion of the QRS
- QRS prolongation >110ms
What are features suggestive of VT?
- AV dissociation
- Capture beats
- Fusion beats
- North-west axis
- Broad QRS complexes
- Negative concordance
What are the ecg features of AF with complete heart block?
- Fibrillatory baseline, absence of P waves
- Slow rate of 50
- R-R intervals regular
- QRS narrow suggestive of supra-Hisian escape rhythm
