Atrial Rhythms and SVT

Narrow-complex tachycardias that start above the ventricles

Cardiac & EKG

Atrial fibrillation (A-fib)

Irregularly irregular, no P waves

RateAtrial 350–600 (chaotic); ventricular varies (RVR >100)

RhythmIrregularly irregular

P waveNone: wavy fibrillatory baseline

PRNone (cannot measure)

QRSUsually <0.12 s

Main danger: stroke. Blood pools in the left atrial appendage → clot → embolic stroke. Loss of "atrial kick" also ↓ cardiac output.
Causes: HTN, CAD, HF, valve disease, age, hyperthyroidism, alcohol, sleep apnea, obesity, after heart surgery.
Assess: apical pulse for a full minute (pulse deficit), palpitations, fatigue, dyspnea, dizziness.

Treatment:

Unstable → synchronized cardioversion.
Rate control: beta blocker (metoprolol), diltiazem (not in HFrEF), digoxin.
Rhythm control: cardioversion, amiodarone and others, catheter ablation.
A-fib ≥48 h or unknown: anticoagulate ≥3 weeks or TEE before elective cardioversion, and ≥4 weeks after.
Anticoagulation by CHA₂DS₂-VASc score: DOACs preferred over warfarin, except mechanical valve or moderate–severe mitral stenosis (warfarin). Updated

Atrial flutter

Sawtooth waves

Atrial rate250–350

VentricularDepends on ratio: 2:1 ≈150, 4:1 ≈75

RhythmUsually regular

P waves replaced by sawtooth flutter waves (best in II, III, aVF); PR not measurable; QRS narrow. A regular narrow rhythm at exactly ~150 → think flutter with 2:1 block.
Treatment: same rules as A-fib (rate control, cardioversion, anticoagulation). Catheter ablation is often curative.

SVT

Sudden start, sudden stop

Rate150–250

RhythmRegular

P / QRSP hidden; QRS narrow

Stable: vagal maneuvers (modified Valsalva), then adenosine 6 mg rapid IV push into a proximal IV followed immediately by a 20 mL saline flush; if needed 12 mg. Warn: brief chest pressure, flushing, and a few seconds of asystole on the monitor are expected. Run a strip.
Unstable: synchronized cardioversion.

CHA₂DS₂-VASc (stroke risk in A-fib)

C CHF	1	H Hypertension	1
A₂ Age ≥75	2	D Diabetes	1
S₂ Stroke/TIA/thromboembolism	2	V Vascular disease (MI, PAD)	1
A Age 65–74	1	Sc Sex category (female)	1

Anticoagulation recommended at ≥2 (men) or ≥3 (women); considered at 1 (men) or 2 (women).

Priority Unstable = hypotension, acutely altered mental status, signs of shock, ischemic chest pain, or acute heart failure. Any unstable tachycardia with a pulse → synchronized cardioversion.

Adenosine and diltiazem are avoided in A-fib with a wide, very fast, irregular QRS (possible WPW): they can trigger VF.