Comprehensive Guide to Cardiac Dysrhythmias: Atrial, Junctional, AV Block, and Ventricular Rhythms

1. Atrial Dysrhythmias

• Premature Atrial Complexes (PACs)

  • Key Feature: Early beat originating outside the SA node in the atria.

  • P Wave: Upright preceding QRS, but morphology differs from normal sinus $P$ waves.

  • PR Interval (PRI): Normal $0.12\text{ to }0.20\,s$ ($120\text{ to }200\,ms$); may vary slightly.

  • QRS Duration: Narrow ($\le 0.11\,s$ / $110\,ms$).

  • Rhythm & Rate: Underlying rhythm rate; PACs make overall rhythm irregular.

  • Causes: Stress, caffeine, heart failure, electrolyte imbalance.

  • Management: Infrequent requires no treatment; frequent requires treating the underlying cause.

• Atrial Flutter

  • Key Feature: Rapid atrial focus firing faster than ventricles can follow.

  • P Wave: Classic $P$ waves absent; replaced by sawtooth / picket-fence flutter ($F$) waves.

  • Rates: Atrial rate $240\text{ to }320\,\text{beats/min}$; Ventricular rate $60\text{ to }160\,\text{beats/min}$.

  • Rhythm: Usually regular with constant conduction ratio (e.g., $2:1$ conduction).

  • PRI: $0.12\text{ to }0.20\,s$ ($120\text{ to }200\,ms$) for conducted beats; QRS $\le 0.11\,s$ ($110\,ms$).

  • Management: Cardioversion or rate-control drugs; prehospital care is usually limited unless critical.

• Atrial Fibrillation (A-Fib)

  • Key Feature: Chaotic atrial baseline quivering without organized atrial contraction.

  • ECG Hallmark: Irregularly irregular rhythm with no visible $P$ waves or measurable PRI.

  • QRS Duration: Narrow ($\le 0.11\,s$ / $110\,ms$).

  • Complication: Blood stasis in non-contracting atria leads to clot formation and stroke risk.

  • Medications: Anticoagulants + rate-control drugs (beta-blockers, calcium channel blockers).

• Multifocal Atrial Tachycardia (MAT)

  • Key Feature: Tachycardic wandering atrial pacemaker with $\ge 3$ distinct $P$ wave shapes.

  • Rate & Rhythm: Rate $> 100\,\text{beats/min}$; irregularly irregular rhythm.

  • PRI & QRS: PRI $0.12\text{ to }0.20\,s$ ($120\text{ to }200\,ms$); QRS $\le 0.11\,s$ ($110\,ms$).

  • Associated Conditions: Severe COPD/lung disease, pulmonary hypertension, hypomagnesemia, theophylline use.

  • Management: Standard SVT treatments fail; deferred to emergency department.

• Supraventricular Tachycardia (SVT)

  • Key Feature: Rapid regular rhythm originating above ventricles at rate $> 100\,\text{beats/min}$ (often $> 150\,\text{beats/min}$ at rest).

  • Hemodynamic Effect: Rates $> 150\,\text{beats/min}$ reduce ventricular filling time and severely drop stroke volume.

  • ECG: Regular R-R intervals; $P$ waves often buried in preceding $T$ waves; narrow QRS ($\le 0.11\,s$ / $110\,ms$).

  • Reentrant Types:

  • AVNRT: Reentry circuit within/near the AV node (most common PSVT).

  • AVRT: Accessory pathway bridging atria and ventricles (e.g., WPW syndrome).

2. Junctional Rhythms and Conduction Abnormalities

• Physiology of the AV Junction

  • Secondary Pacemaker Rate: $40\text{ to }60\,\text{beats/min}$.

  • Retrograde P Wave Patterns:

  1. Inverted P before QRS: Atrial conduction before ventricular depolarization (PRI $< 0.12\,s$ / $120\,ms$).

  2. Hidden P Wave: Simultaneous depolarization obscures $P$ wave inside QRS (flat baseline).

  3. Inverted P after QRS: Atrial depolarization delayed relative to ventricles.

• Junctional Spectrum Comparison (Quick Memory Chart)

  • Junctional Escape Rhythm: Rate $40\text{ to }60\,\text{beats/min}$ | Regular | Treated with Atropine or TCP if symptomatic.

  • Accelerated Junctional Rhythm: Rate $60\text{ to }100\,\text{beats/min}$ | Regular | Usually asymptomatic.

  • Junctional Tachycardia: Rate $> 100\,\text{beats/min}$ | Regular | If rate $> 150\,\text{beats/min}$, managed as SVT.

  • Premature Junctional Complex (PJC): Early ectopic beat | Irregular overall rhythm | Precursor to complex dysrhythmias.

3. Atrioventricular (AV) Blocks

• First-Degree AV Block

  • Rule: "If the R is far from P, then you have a First Degree."

  • ECG: Regular; upright $1:1$ $P$ waves; prolonged constant PRI ($> 0.20\,s$ / $200\,ms$); narrow QRS ($\le 0.11\,s$).

• Second-Degree AV Block: Mobitz Type I (Wenckebach)

  • Rule: "Longer, longer, longer, drop! Then you have a Wenckebach."

  • ECG: Irregular; progressive lengthening of PRI until a $P$ wave is dropped without a QRS.

• Second-Degree AV Block: Mobitz Type II (Classical)

  • Rule: "If some Ps don't get through, then you have a Mobitz II."

  • ECG: Regular or irregular; constant PRI on conducted beats with intermittent nonconducted $P$ waves.

  • Risk: High risk of progressing to complete heart block; often requires Transcutaneous Pacing (TCP).

• Third-Degree AV Block (Complete Heart Block)

  • Rule: "If Ps and Qs don't agree, then you have a Type III."

  • ECG: Complete AV dissociation. Regular P-P intervals and regular R-R intervals, but completely independent. No relationship between $P$ waves and QRS.

  • QRS & Treatment: Narrow QRS = high junctional origin (may respond to atropine); Wide QRS = ventricular escape (requires immediate TCP).

4. Ventricular Dysrhythmias

• General Rules: Conduction via slow cell-to-cell spread creates wide QRS complexes ($\ge 0.12\,s$ / $120\,ms$). Intrinsic ventricular rate is $20\text{ to }40\,\text{beats/min}$.

• Idioventricular Rhythm

  • Rate: $20\text{ to }40\,\text{beats/min}$.

  • ECG: Regular, no $P$ waves, wide QRS ($\ge 0.12\,s$).

  • Clinical State: Severe hemodynamic compromise.

• Accelerated Idioventricular Rhythm (AIVR)

  • Rate: $40\text{ to }100\,\text{beats/min}$.

  • ECG: Regular, no $P$ waves, wide QRS ($\ge 0.12\,s$).

  • Significance: Classically seen after successful reperfusion therapy for acute myocardial infarction (AMI); benign and self-limiting.

• Ventricular Tachycardia (VT)

  • Definition: $\ge 3$ consecutive ventricular beats at rate $> 100\,\text{beats/min}$ with wide QRS ($\ge 0.12\,s$).

  • Morphologies:

  • Monomorphic VT: Uniform QRS shape across the lead.

  • Polymorphic VT / Torsades de Pointes: QRS continuously varies in shape, twisting around baseline. Torsades occurs primarily with prolonged QT intervals.

  • Emergency Interventions:

  • Pulseless VT: CPR + immediate unsynchronized defibrillation.

  • Unstable VT (hypotension, chest pain, pulmonary edema): Immediate synchronized cardioversion.