Cardiac Arrhythmias & Conduction Blocks – Vocabulary Review

Clinical Flags & Navigation Hints

• Slides marked with red bars on the side ➜ “notify doctor”. These slides identify rhythms that demand immediate clinical escalation.
• Presenter: Justin Cleveland, MD, MS | Course: Allen School of Health Sciences.

Sinus Rhythms

• Definition & Identification
  • Normal pacemaker: SA node.
  • Sequence: P ➜ QRS ➜ T repeating at a steady cadence.
  • Rate clue: Normal, "normocardic" rhythm when RR interval ≈ 3-5 small boxes on standard 25\,\text{mm/s} paper.
  • Visual trick: "Train your eyes to see the coupled T and P waves between each QRS."
  • Practical tip: Always scan multiple leads; pick the one with clearest waveforms. In the example, lead aVR is reversed—this is normal and need not be mistaken for pathology.
• Clinical relevance
  • A true, clean sinus rhythm is the reference frame for spotting pathology.
  • Establishes baseline PR, QRS, QT intervals for the patient.

Premature Complexes

Premature Atrial Complexes (PACs)

• Hallmark: Early ectopic P′ wave (different morphology) followed by usually normal QRS.
• In the strip: 2nd & 5th P waves arrive early → shortened abnormal RR (red) vs baseline RR (green).
• Why it matters
  • May precede atrial tachyarrhythmias (flutter/fibrillation).
  • Often benign but can trigger palpitations; frequency guides work-up.

Premature Ventricular Complexes (PVCs)

• Identification
  • Wide, bizarre QRS not preceded by P; generally followed by compensatory pause.
  • Example strip shows bigeminy: pattern of normal beat + PVC repeating.
• Lead labeling reminder: Strip displayed several chest & limb leads (aVR, V4–V6…).
• Clinical note
  • In isolation often benign; runs (≥ 3) can become VT.
  • Electrolyte imbalance, hypoxia, or drug effects are common reversible causes.

Atrial Arrhythmias

Atrial Flutter

• Sawtooth F-waves best in inferior leads.
• Key differentiators
  1. Rule-out sinus tachycardia: P/T waves not rounded.
  2. Rule-out AFib: Flutter is classically regular (e.g., 2{:}1 or 4{:}1 conduction).
• Clinical significance
  • High stroke risk → anticoagulation.
  • May respond to rate control or ablation.

Atrial Fibrillation

• No discernible P waves; baseline fibrillatory oscillations.
• Irregularly irregular RR—best appreciated on long lead II strip.
• Diagnostic pearl: Even if V1 mimics a sawtooth, the rhythm irregularity eliminates flutter.
• Pattern-recognition tip
  • First, spot the narrowest RR intervals; then compare to the widest to confirm variability.
• Clinical stakes: Anticoagulation guided by CHA2DS2-VASc, rate vs rhythm control debates, cardioversion timing (\< 48 h or TEE guided).

Atrioventricular (Heart) Blocks

First-Degree AV Block

• Regular rhythm, PR > 1 big box (>{200}\,\text{ms}).
• Benign in many; can hint at drug effect (beta-blockers, digoxin) or ischemia.

Second-Degree AV Block

1. Mobitz Type I (Wenckebach)
   • Mnemonic: “Going … going … going … DROP.”
   • Progressive PR prolongation (orange) until a non-conducted P (red).
   • Usually nodal; often transient, vagally mediated.
2. Mobitz Type II
   • Fixed PR with intermittent dropped QRS.
   • Intrahisian/infra-His → high risk for progression to complete block ⇒ pacing considered.

Third-Degree (Complete) AV Block

• Total dissociation: P rate independent of QRS rate.
• Example: Red arrows mark P waves; T waves follow QRS.
• One P hidden inside a QRS.
• Clinical urgency: Usually symptomatic (syncope, dizziness); requires pacing.

ST-Elevation Myocardial Infarction (STEMI) Recognition

• Criteria on example: QRS blends into ST/T segment.
• Precordial polarity
  • Leads V1–V3: inverted QRS.
  • V4–V6: upright but subtle STE (V5 subtle, V6 very subtle).
• Importance: Early cath lab activation saves myocardium ("time = muscle").

Ventricular Arrhythmias

Ventricular Tachycardia (VT)

• Regular wide-complex tachycardia. Regularity rules out VF.
• Subtypes: monomorphic vs polymorphic (e.g., Torsades).
• Unstable VT ⇒ synchronized cardioversion.

Ventricular Fibrillation (VF)

• Chaotic, irregular baseline, no discernible QRS.
• "Train your eyes": absence of repeating morphology.
• Requires immediate defibrillation.

Torsades de Pointes

• Polymorphic VT with waxing/waning QRS amplitude (“twisting of the points”).
• Slide looked atypical: calmer spikes bracketed by larger ones.
• Often due to prolonged QT (meds, electrolyte issues). Treat with Mg^{2+} & overdrive pacing.

Agonal Rhythm

• Extremely slow, wide, often irregular ventricular escape rhythm.
• Slide note: Frequency range 0.5{-}27\,\text{Hz} displayed.
• Represents near-terminal electrical activity; CPR & epinephrine indicated.

Asystole

• Flat-line (\le 1 mm variability) for \ge 6 s defines asystole on ACLS monitors.
• Case presented: 23-second run; patient symptom: “feeling disoriented.”
• Management per ACLS: CPR, epinephrine, identify reversible causes (H’s & T’s); here proceeded to permanent pacemaker.

Case Study Highlights (Slide 19)

• Hx: TIA, mitral valve replacement (2010), atrial flutter ablated (2018), paroxysmal atrial tachycardia, mild diastolic dysfunction, prior 500+ runs of PAT on Holter.
• Med timeline
  • Carvedilol & flecainide started, later stopped due to brady + junctional escape.
  • At presentation: only HCTZ; on hold for pacemaker ➜ aspirin & warfarin held.
• Symptoms: Weekly "closing in" episodes, dim vision, memory lapses, no palpitations, occasional extreme fatigue.
• In-hospital event: During EEG sleep phase, telemetry captured 23 s asystole ⇒ awakened disoriented.
• 12-lead: Mild 1st-degree AVB with PR =240\,\text{ms}; otherwise normal.
• Key learning
  • Long sinus pauses/asystole can masquerade as TIAs or syncope‐like spells.
  • Holter/implantable loop recorders invaluable for correlation.

Pattern-Recognition & Study Tips

• Start broad ➜ focus: Is rhythm regular? Narrow vs wide QRS? Presence of P?
• Lead choice matters: For P waves, inferior leads; for flutter, V1; for STE, leads over infarct territory.
• Box counting
  • 1 big box = 200\,\text{ms} (PR & QT landmarks).
  • 300/150/100/75/60/50 rule for quick rate from single lead.
• Mnemonic recap
  • Wenkebach: “Longer longer longer drop.”
  • VT vs VF: “Regular = Tachy, chaotic = Fib.”
• Ethical/clinical implication: Prompt recognition & escalation saves lives—especially blocks > Mobitz II, VT, VF, STEMI, and asystole.