ECG Rhythm Recognition, ACS Basics, and Acute Management

Rhythm recognition basics (overview)

• Winky box mnemonic: progressively longer intervals (PR) between P and QRS until a QRS is dropped; used to identify first-degree and Wenckebach-type patterns. The idea is that PQRS becomes increasingly spaced, then a QRS drops, and the pattern repeats.
• First-degree AV block and Winky box are the easiest blocks to identify by rhythm strip.
• Second-degree AV block has two subtypes:
  • Type I (Wenckebach): progressively longer PR intervals until a QRS is dropped. Pattern shows a gradually lengthening PR, then a dropped QRS, then repeats.
  • Type II: intermittent dropped QRS with a relatively constant PR interval; there is usually a P wave before every QRS when a QRS is present, but some QRS complexes are missing.
• Third-degree (complete) AV block: no fixed relationship between P waves and QRS complexes; atria and ventricles beat independently; typically very slow ventricular rate (e.g., around $30$ bpm is common) and patients may require pacing.
• Distinguishing blocks is important for management decisions (pace vs continue monitoring).

Atrioventricular blocks in detail

• First-degree AV block
  • Definition: delayed conduction from SA node to AV node; PR interval prolonged but constant; one-to-one atrial-to-ventricular conduction always present.
  • How it looks: all PR intervals are longer than normal, but each P is followed by a QRS in the same pattern.
• Second-degree AV block Type I (Wenckebach)
  • Progressive lengthening of PR interval with each beat until a QRS is dropped.
  • Pattern repeats (cycle length varies).
• Second-degree AV block Type II
  • PR interval remains constant; intermittent dropped QRS complexes.
  • There is a P wave before every QRS when QRS is present, but some QRS complexes are missing.
• Third-degree AV block (complete block)
  • No relationship between P waves and QRS; atrial rhythm independent of ventricular rhythm.
  • Often requires permanent pacemaker; can cause syncope or hemodynamic instability.

Practical notes on rhythm pattern recognition

• When reviewing a strip, ask:
  • Is there a P wave before every QRS? If yes, rhythm may be supraventricular; if not, may be heart block or other rhythm.
  • Are the PR intervals constant or progressively lengthening?
  • Is a QRS dropped at regular intervals (second-degree type I or II) or is there complete dissociation (third-degree)?
• Remember the clinical clues: third-degree blocks often present with fatigue, dizziness, or syncope due to very slow rate; pacing is usually required.

Atrial arrhythmias: AFib vs AFlutter

• Atrial fibrillation (AFib)
  • Multiple, irregularly oriented atrial impulses produce rapid, chaotic atrial activity.
  • Rhythm: irregularly irregular; QRS intervals vary; P waves are replaced by fibrillatory (f) waves, often described as tiny, irregular undulations.
  • Clinical significance: high risk of atrial thrombi and embolic stroke; risk of systemic embolization if not anticoagulated.
  • Management: rate control, rhythm control, and often anticoagulation; if new-onset AFib with rapid ventricular response (RVR), electrical cardioversion may be considered after anticoagulation when appropriate.
• Atrial flutter (AFlutter)
  • Sawtooth saw pattern in the atrial activity (f waves) with a more regular ventricular response depending on AV conduction.
  • Typically caused by a single reentrant circuit in the atria; P waves aren’t seen as discrete P waves but as flutter waves.
  • Rate control and anticoagulation are used; rhythm control may be pursued depending on stability and duration.

EKG leads, placement, and what they show

• 12-lead EKG basics
  • 6 precordial leads: V1, V2, V3, V4, V5, V6 placed across the chest (anterior/septal to lateral regions).
  • 4 limb leads: I, II, III, aVR, aVL, aVF (often shown in standard limb lead format).
  • A standard 12-lead EKG provides 12 views of the heart’s electrical activity from different angles; there are 10 physical leads placed on the patient, yielding 12 views.
  • Higher-density configurations (e.g., 18-lead) exist but are not standard in all settings.
• Localizing myocardial infarction by leads
  • Septal MI: ST elevation in V1–V2; sometimes V3.
  • Anterior MI: ST elevation in V3–V4.
  • Lateral MI: ST elevation in I, aVL, V5–V6.
  • Inferior MI: ST elevation in II, III, aVF.
• “Sally” mnemonic (as discussed in lecture) for locating ST elevations by leads; normal clinical practice uses the standard anatomical mapping above plus correlating leads to regions.
• Interpreting ST changes
  • ST elevation in corresponding leads suggests acute myocardial injury in that region (STEMI).
  • ST elevation is a time-critical finding requiring rapid intervention (cath lab; door-to-balloon goal of $ext{within } 90 ext{ minutes}$ when possible).
  • ST depression can indicate ischemia or reciprocal changes.
  • Tall peaked T waves can indicate hyperkalemia, which may alter the appearance of the strip and mimic other changes; electrolyte abnormalities can cause dysrhythmias.

STEMI vs NSTEMI and emergent management

• STEMI = ST elevation myocardial infarction
  • Leads showing ST elevation guide the suspected infarct location and urgency for urgent reperfusion.
  • Protocol: activate cath lab; time-to-intervention goal commonly within $90$ minutes from first medical contact (door-to-balloon).
• NSTEMI = non-ST elevation myocardial infarction
  • No ST elevation on EKG; troponin elevation with chest pain or equivalent symptoms.
  • Management involves risk stratification, medical therapy, and possible coronary intervention but not immediate STEMI cath lab activation unless clinical trajectory worsens.
• Troponin and high-sensitivity assays
  • Troponin levels (cardiac enzymes) are elevated in MI; high-sensitivity troponin assays can detect lower levels earlier and may show values in the hundreds or thousands (e.g., $1{,}500$) rather than the old threshold of 0.04.
  • Serial testing and clinical correlation are essential.
• Door-to-balloon and core measures
  • Time-sensitive language emphasizes getting a patient with STEMI to PCI (percutaneous coronary intervention) within the target window to minimize tissue death.
  • If no PCI-capable facility, EMS transfer to the nearest facility with a cath lab is necessary; coordination with the receiving center is critical.

EKG patterns: tall T waves, QRS patterns, and localized changes

• Tall peak T waves can indicate hyperkalemia; the monitor may mis-count a tall T wave as a QRS complex, affecting HR calculation on the strip.
• QRS morphology in blocks and bundle branch blocks can mimic or mask other patterns; classic “rabbit ears” or “Himalayas” describe bifascicular/ventricular conduction abnormalities.
• If there is ST elevation in multiple leads (e.g., I, aVL, V5, V6), this supports a lateral MI; mapping leads to regions helps guide therapy.

Bundle branch blocks

• Manifestations: abnormal QRS morphology; can show characteristic notching or “rabbit ears” depending on the lead placement.
• Effect on interpretation: BBB can complicate the identification of ischemia due to altered QRS duration and T-wave relationships.

Pacemakers: rhythm with pacing and capture

• Temporary vs permanent pacing
  • Temporary pacemaker: used in acute settings (often within days) to stabilize rhythm until a permanent solution is placed.
  • Permanent pacemaker: implanted to provide ongoing rhythm support.
• Identifying paced rhythms
  • Pacemaker spikes (pacing stimuli) precede the QRS complex or P wave depending on the chamber paced.
  • Capture refers to the pacemaker spike reliably producing a corresponding cardiac complex (QRS or P wave).
  • Loss of capture means pacing stimulus occurs but does not trigger a cardiac complex; power may need adjustment per physician order.
• Types of pacing
  • Atrial pacing, ventricular pacing, or dual-chamber pacing (both atria and ventricle).
• Transvenous vs transcutaneous pacing
  • Transvenous: leads threaded via veins to the heart.
  • Transcutaneous: external pads deliver pacing; used as a temporary bridge in emergencies.

Premature ventricular contractions (PVCs)

• Unifocal PVCs: PVCs that arise from the same focus, all appear with the same morphology.
• Multifocal PVCs: PVCs arising from different foci, morphologies differ.
• Patterns
  • Bigeminy: every other beat is a PVC.
  • Trigeminy: every third beat is a PVC.
  • Quadrigeminy: every fourth beat is a PVC.
• Ventricular tachycardia (VT)
  • Defined as more than $3$ consecutive PVCs.
  • VT can be stable (patient has a pulse) or unstable (no pulse; requires immediate treatment).
  • VT can be narrow or wide QRS; stability guides treatment strategy.
• Ventricular fibrillation (VF)
  • Chaotic, irregular rhythm with no discernible QRS; pulseless; requires immediate CPR and defibrillation.
• Cardiac arrest management
  • For VT with pulse: synchronized cardioversion.
  • For VT without pulse or VF: unsynchronized defibrillation (shock) and CPR; AEDs can detect and deliver shocks for VT/VF but not for asystole.
  • Asystole: flatline with no electrical activity; not shockable; continue CPR and manage underlying causes.

AEDs and cardioverting strategies

• Automated external defibrillators (AEDs)
  • AEDs can identify VT, VF, and sometimes advise shocks; they do not shock asystole.
  • Stand clear protocol: ensure everyone is clear of the patient before delivering a shock.
• Electrical cardioversion
  • Used for unstable rhythms (e.g., AFib with RVR, VT with pulse) where a synchronized shock is delivered to terminate a tachyarrhythmia while avoiding shock on the R wave.
  • Synchronized mode shows a spike on the monitor to time the shock with a safe moment in the QRS complex.

Angina and acute management considerations

• Stable vs unstable angina
  • Stable angina: chest pain with exertion that resolves with rest or nitro; relief with nitroglycerin typically expected.
  • Unstable angina: chest pain at rest or increasing in frequency/severity; time-critical evaluation and escalation.
• Nitroglycerin use
  • Sublingual nitro can relieve angina; repeated dosing up to three times may be used.
  • If chest pain persists after nitro, seek emergency care immediately; delays can worsen myocardial injury and cath lab timing.
• Acute coronary syndrome (ACS) workflow
  • For suspected MI, rapid assessment, stat ECG, and troponin draw.
  • If STEMI is identified, call for rapid cath lab activation and transport to PCI-capable facility.
• Symptoms differences in women
  • Women may present with more generalized symptoms (fatigue, dyspnea, or atypical chest discomfort) rather than classic heavy chest pain.
• High-risk populations
  • Diabetic patients are at higher risk for heart disease and may present atypically; vigilance in assessment is crucial.

Diet, lifestyle, and risk factors for heart disease

• Heart-healthy diet principles
  • Low sodium intake; emphasis on fish (omega-3 fatty acids) and reduced red meat consumption; avoid fried foods and excessive refined carbs.
• Lifestyle and risk factors
  • Diabetes elevates risk; obesity, hypertension, smoking, and sedentary lifestyle contribute to MI risk.
• Practical patient education points
  • Teach patients about nitro use, recognizing symptoms, and when to seek emergency care.
  • Encourage adherence to prescribed antithrombotic therapy for chronic AFib when applicable.

Evaluation and clinical reasoning tips for exam questions

• Always start with an initial assessment and obtain vital signs to evaluate any intervention’s effectiveness.
• If a question asks how to evaluate an intervention, it typically requires a before-and-after comparison (vital signs, symptoms, objective data).
• In rhythm interpretation questions, assess P waves, PR interval behavior, and relationship between P waves and QRS complexes; use that to distinguish first-degree block, second-degree Type I/II, and third-degree block.
• For chest pain questions, differentiate stable versus unstable angina; consider nitro use and EMS activation timing; recognize door-to-balloon timing targets for STEMI.
• Recognize that hyperkalemia can alter T waves and other ECG features; check electrolytes when discrepancies arise.
• In AED/CPR scenarios, emphasize rapid response: call 911, retrieve AED, and perform CPR until defibrillation or advanced care arrives.
• When discussing pacemakers, know how to identify capture on the rhythm strip and the meaning of pacer spikes in relation to P waves or QRS complexes.
• Be aware of the clinical implications of rhythm patterns: pacing for complete AV block, anticoagulation considerations in AFib, and the urgency of reperfusion in STEMI.

Quick reference recap (key takeaways)

• AV blocks: First-degree (prolonged but consistent PR), Second-degree Type I (Wenckebach: progressive PR lengthening, dropped QRS), Second-degree Type II (constant PR with dropped QRS), Third-degree (complete dissociation, may require pacing).
• Atrial arrhythmias: AFib (irregularly irregular, risk of clots) vs AFlutter (sawtooth pattern).
• ECG leads: 12-lead EKG provides regional localization (septal/anterior/lateral/inferior) via leads V1–V6 and I, II, III, aVR, aVL, aVF.
• STEMI vs NSTEMI: ST elevation with immediate cath lab; NSTEMI with troponin elevation but no ST elevation.
• VT/VF/AED: VT with or without pulse; VF pulseless; use synchronized cardioversion for VT with pulse, defibrillation for VT without pulse or VF; CPR and AED in both.
• Pacemakers: spikes indicate pacing; capture is essential; loss of capture requires adjustment per physician order.
• Angina management: nitro, rapid assessment, EMS if not relieved; distinguish stable vs unstable.
• Lifestyle: diet changes, weight, diabetes management, blood pressure control, smoking cessation.