CardiologyTier 1Disease (DEADMAN)

Cardiac arrhythmias - atrial flutter

Description

Macro-re-entrant atrial tachycardia with an organised atrial rate of ~300/min (250-350)
Ventricular rate = atrial rate / conduction ratio
- 2:1 -> 150 bpm (the commonest presentation; "regular narrow tachycardia at 150" = flutter until excluded)
- 3:1 -> 100, 4:1 -> 75; variable block -> irregular

Typical (cavotricuspid isthmus-dependent) - ~90%

Circuit in the right atrium around the tricuspid annulus, through the cavotricuspid isthmus (CTI)
Counterclockwise (typical, ~90%): negative sawtooth F waves in II, III, aVF, positive in V1
Clockwise (reverse typical): positive in inferior leads, negative in V1

Atypical (non-CTI-dependent)

Left atrial, peri-mitral, roof-dependent, or scar/incisional re-entry
Post AF ablation, post cardiac surgery, post Fontan/atriotomy, atrial cardiomyopathy
Variable morphology; ablation is harder and lower-yield

Requires an anatomical barrier (tricuspid annulus, crista terminalis, eustachian ridge, surgical scar) + an area of slow conduction (the CTI)
-> stable macro-re-entrant wavefront; AV node filters the rate

Substrate / precipitants

Atrial stretch: mitral or tricuspid valve disease, HF, HTN, congenital heart disease (ASD)
Pulmonary: COPD, PE, OSA, pneumonia (right atrial disease)
Post-operative: cardiac and thoracic surgery (peak day 2-4)
Thyrotoxicosis, alcohol, sepsis, electrolyte disturbance
Antiarrhythmic drugs: flecainide or propafenone given for AF can organise it into flutter with 1:1 conduction ("class IC flutter" - slows the atrial rate to ~200, which the AV node conducts 1:1 -> ~200 bpm wide complex. Always co-prescribe an AV nodal blocker)
Post AF ablation

ECG

Sawtooth flutter (F) waves with no isoelectric baseline in II, III, aVF; discrete upright waves often best seen in V1
Rate ~300 with fixed ratio -> rigidly regular ventricular rate
2:1 flutter hides alternate F waves inside the QRS/T - suspect any regular narrow tachycardia at ~150 bpm
Unmasking manoeuvres: vagal manoeuvre or IV adenosine -> transient AV block reveals the flutter waves
- Adenosine is diagnostic, not therapeutic, here
Lewis lead placement, or prolonged rhythm strip in V1

Distinguish from

	Feature
Sinus tachycardia	Rate varies with activity, P waves upright II
AVNRT/AVRT	Abrupt on/off, terminates with adenosine
AF	Irregularly irregular, no organised atrial activity
Atrial tachycardia	Rate 150-250, isoelectric baseline between P waves

Work-up

TTE - atrial size, valve disease, LV function, thrombus risk
TFT, UEC, FBE
Consider PE/OSA if context fits
Assess for tachycardia-mediated cardiomyopathy if rate has been uncontrolled: EF may recover fully after rhythm restoration

A. Haemodynamically unstable

Synchronised DC cardioversion - flutter cardioverts at low energy (50 J often sufficient)

B. Rate control - harder than in AF

Beta blocker (metoprolol) or non-dihydropyridine CCB (verapamil/diltiazem) IV then oral
Digoxin as an add-on, especially in HF
Flutter is characteristically resistant to rate control - drifting between 2:1 and 4:1 gives poor symptom control. This is why rhythm control is favoured earlier than in AF

C. Rhythm control

Electrical cardioversion - high success (>95%), low energy
Overdrive atrial pacing - via existing pacemaker leads or transoesophageal; useful post-cardiac surgery
Pharmacological conversion less effective than in AF; ibutilide is the best (QT prolongation, torsades - monitored setting)
Amiodarone for rate and rhythm in the critically ill

D. Catheter ablation - the definitive treatment

CTI ablation (bidirectional block) for typical flutter: success >95%, recurrence <5%
- Low complication rate; Class I as first-line therapy for symptomatic typical flutter, not just after drug failure
Atypical flutter: requires 3D mapping, lower success, often part of an AF ablation strategy
Warn the patient: ~30% develop AF within 5 years after successful flutter ablation - ablation cures the flutter, not the atrial substrate. Anticoagulation decisions continue

E. Anticoagulation - identical rules to AF

Thromboembolic risk is comparable to AF - the common error is assuming flutter is safer
CHA2DS2-VA score (the sex category has been removed from the contemporary ESC score)
- Anticoagulate if score >=2; consider if 1
DOAC preferred over warfarin unless mechanical valve or moderate-severe mitral stenosis
Peri-cardioversion: anticoagulate 3 weeks before and 4 weeks after, or TOE-guided if <48 h / urgent
- Continue for 4 weeks after cardioversion regardless of score - atrial stunning
Continue long-term based on stroke risk score, not on rhythm outcome

F. Treat the substrate

Atrial fibrillation - coexists or follows in the majority
ASD and congenital heart disease, especially post-Fontan/Mustard/Senning (intra-atrial re-entrant tachycardia)
COPD and cor pulmonale; OSA
Thyrotoxicosis
Post cardiac surgery (up to 30% of CABG patients get AF/flutter)
Flecainide/propafenone-induced 1:1 flutter
Rheumatic and degenerative mitral valve disease
Tachycardia-mediated cardiomyopathy

Rarely truly paroxysmal for long - tends to become persistent or degenerate into AF
Untreated, sustained rapid ventricular response -> tachycardia-mediated cardiomyopathy (potentially fully reversible)
Post CTI ablation: flutter recurrence <5%, but AF in ~30% at 5 years
Stroke risk equals AF; anticoagulation decisions are lifelong and independent of ablation success
1:1 conduction (300 bpm) is the catastrophic complication - occurs with sympathetic drive, class IC drugs, or an accessory pathway

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