Rapid Review·Cardiovascular
Select any text to highlight it or add a note.
PATHOLOGY
T1Must knowNarrow Complex Tachycardias
P310
Videos
4 to play here
Play 4 here
Focus on
Rhythms from at or above the AV node, and the one accessory pathway that inverts all the usual drug rules.
Key takeaways
Why narrow means supraventricular
Narrow QRS under 120 msec
the ventricles were activated rapidly through the normal conduction system, so the tachycardia originates within or above the AV node, i.e. it is supraventricular. WPW is the exception, since its QRS is widened.Atrial fibrillation
ECG
irregularly irregular rate and rhythm with NO discrete P waves, as on the atrial fibrillation tracing. It is often paroxysmal, so continuous monitoring may be needed to catch it. Patients may be asymptomatic, or notice palpitations, dyspnea, and fatigue.Where it comes from
arrhythmogenic foci usually sit near the pulmonary vein ostia in the left atrium, which is precisely what pulmonary vein ablation targets. The catheter enters the right heart through the SVC or IVC and crosses the interatrial septum at the foramen ovale to reach them. Alcohol and a high sympathetic drive can set the foci off.Risk factors
anything that remodels the atria: age-related myocardial change (the strongest), atrial enlargement from heart disease (hypertension, mitral stenosis), coronary artery disease. AF begets AF: each episode shortens the atrial refractory period and slows conduction, so ectopic foci and reentry persist and later episodes come more easily.Complication
thromboembolism from left atrial stasis, and the LA appendage is the commonest thrombus site.Management, by "ABCD"
Anticoagulation, Beta-blockers, Calcium channel blockers, Digoxin, plus cardioversion or ablation.| Rhythm control | Rate control |
|---|---|
| Electrical cardioversion | AV node blockade: beta-blockers, non-dihydropyridine CCBs, digoxin (which raises parasympathetic tone) |
| Antiarrhythmics: flecainide, amiodarone | |
| Radiofrequency ablation of the pulmonary vein ostia (definitive) | |
| Anticoagulation often indicated | Anticoagulation usually indicated |
The other supraventricular rhythms
Multifocal atrial tachycardia
irregularly irregular with 3 or more distinct P wave morphologies, from multiple ectopic atrial foci, as on the MAT tracing. Associated with COPD, pneumonia, and heart failure.Atrial flutter
rapid identical consecutive atrial depolarizations giving "sawtooth" P waves with a regular RR interval, as on the atrial flutter tracing. The reentry circuit runs around the tricuspid annulus through the cavotricuspid isthmus, as drawn on the flutter reentry circuit, and that isthmus is the ablation target. Otherwise treat as for AF.Paroxysmal SVT
any narrow-complex SVT with an abrupt onset (and termination), lasting seconds to days. Most often a reentrant tract, usually within the AV node. Sudden-onset palpitations, lightheadedness, diaphoresis; the ECG on the paroxysmal SVT tracing is regular with the retrograde P waves buried. Terminate by slowing AV nodal conduction with vagal maneuvers (carotid sinus massage, Valsalva, cold water immersion) or adenosine; cardiovert if unstable; definitive treatment is catheter ablation.Wolff-Parkinson-White
What it is
the commonest ventricular pre-excitation syndrome. All three of its states are on the WPW diagram.The pathway
an abnormally fast accessory pathway, the bundle of Kent, bypasses the rate-slowing AV node, so the ventricles partially depolarize early. That gives a delta wave, widened QRS, and shortened PR interval. The pathway can complete a reentry circuit, producing SVT.Treatment
procainamide or ibutilide. AVOID all AV nodal blockers (adenosine, calcium channel blockers, beta-blockers), because blocking the node forces conduction down the accessory pathway and can precipitate ventricular fibrillation.| Feature | Normal SVT | WPW |
|---|---|---|
| Terminate with | Adenosine, CCBs, beta-blockers | Procainamide, ibutilide |
| AV nodal blockers | Are the treatment | CONTRAINDICATED, they force conduction down the accessory pathway |
| ECG | Narrow QRS | Delta wave, wide QRS, short PR |
Side by side
| Arrhythmia | Rhythm | P waves | Key association |
|---|---|---|---|
| Atrial fibrillation | Irregularly irregular | Absent | Pulmonary vein ostia; LA appendage thrombus |
| Multifocal atrial tachycardia | Irregularly irregular | 3 or more morphologies | COPD |
| Atrial flutter | Regular, often 4:1 | "Sawtooth" | Reentry around the tricuspid annulus |
| Paroxysmal SVT | Regular, sudden onset | Often buried in the T wave | AV nodal reentry; terminate with adenosine |
| Feature | Atrial fibrillation | MAT |
|---|---|---|
| Rhythm | Irregularly irregular | Irregularly irregular |
| P waves | None | 3 or more morphologies |
| Setting | Hypertension, CAD, age, atrial dilation | COPD |
A regular tachycardia with a delta wave. Why is adenosine the wrong answer, and what do you give instead?
Blocking the AV node forces every impulse down the bundle of Kent, which can degenerate into ventricular fibrillation. Give procainamide (or ibutilide).
How it's tested
In Wolff-Parkinson-White the usual AV nodal blockers are contraindicated, because blocking the node forces conduction down the accessory pathway and can precipitate ventricular fibrillation, so the answer is procainamide. That single inversion is the most reliable question on this page. Mehlman's atrial fibrillation vignette is worth recognising on sight: an elderly patient with a stroke and a normal blood pressure, where the normal pressure is the clue that the embolus came from the atrium rather than from a carotid plaque, and the next step is a Holter monitor because the AF is paroxysmal.
Go deeper
First Aid 2026 — CV/Pathology (p.310) · B&B — Narrow-complex tachycardias · Mehlman — HY Cardio (AF in the elderly, embolic destinations, CHADS2, WPW)
High-yield images8
Flashcards for this page
Card 1 of 5 · try-out only, nothing is saved
Where are ablations commonly performed in the treatment of atrial fibrillation and in the treatment of atrial flutter?
Atrial fibrillation → (...) and (...)
Atrial flutter → Region between the (...) and the (...)
Atrial fibrillation → (...) and (...)
Atrial flutter → Region between the (...) and the (...)
You just read one page of 944
The rest of Step 1, written exactly like this.
Rapid Review is the reading layer of a full Step 1 platform: a schedule fitted to your exam date, flashcards for every page, and a mentor a message away.
Every Step 1 system
Written the same way: what to know, how it’s tested, where to go deeper.
A plan built to your exam date
Tell us when you sit, and the schedule fits the whole library and your question bank to it.
Flashcards for every page
Ready-made spaced-repetition decks linked to each topic, so nothing you read gets forgotten.
Start 14 days free
No card needed.·See pricing
