Cardio King Lecture / Reimert Tips

Layers of the Heart

• Epicardium: outer layer of the heart.

• Myocardium: middle muscular layer vital for contraction.

• Endocardium: inner lining of the heart.

Blood Flow Through the Heart

1. Blood enters through the superior/inferior vena cava into the right atrium.

2. Flows to the right ventricle via the tricuspid valve.

3. From the right ventricle, blood is pumped through the pulmonary valve to the pulmonary artery and travels to the lungs for oxygenation.

4. Oxygen-rich blood returns to the left atrium via the pulmonary veins.

5. Blood moves to the left ventricle through the mitral valve.

6. The aortic valve delivers oxygen-rich blood from the left ventricle into the aorta, branching into smaller arteries and capillaries, and eventually returns to the heart.

Heart Sounds

• S1 (Lub): Closure of mitral and tricuspid valves.

• S2 (Dub): Closure of aortic and pulmonary valves.

Cardiac Action Potential Phases

1. Resting Membrane Potential: Approximately -85 mV, mainly potassium channels.

2. Depolarization: Rapid influx of sodium ions, causing a spike to +20 mV.

3. Plateau Phase: Calcium channels open, sustaining contraction.

4. Repolarization: Potassium exits the cell, returning to resting state.

Conduction System of the Heart

1. SA Node: Primary pacemaker (60-100 bpm)

2. AV Node: Secondary pacemaker (40-60 bpm)

3. Bundle of His: Sends signals to ventricles.

   • Divides into the right and left bundle branches.

4. Purkinje Fibers: Distributes electrical impulses to ventricles.

ECG Basics

• P Wave: Atrial depolarization, should be smooth and symmetrical.

• QRS Complex: Ventricular depolarization, duration indicates electrical activity status.

• T Wave: Ventricular repolarization, should be upright in most leads.

• QT Interval: Time taken for ventricular depolarization and repolarization, should be <440 ms (men) and <460 ms (women).

EKG Interpretation Steps

1. Assess rhythm - calculate heart rate using boxes method.

2. Examine P Waves, QRS complexes, and T Waves.

3. Determine intervals: PR, QRS, QT.

4. Identify abnormalities based on amplitudes and intervals.

Reimert’s Rhythm Breakdown:

The Three Functions of the Heart

• The heart has three main functions: volume (fluid), pump (physical motor), and electrical conduction system. These work together to maintain circulation.

• A single drop of blood completes the entire cardiac cycle (oxygenated to deoxygenated and back) in one minute.

• The ECG \text{ tracing} reflects two or three of these functions playing out electrically.

The Electrical Conduction System

• Normal sinus rhythm occurs when the electrical system functions perfectly, originating from the sinoatrial (SA) node.

• The SA node is the heart's pacemaker, with an intrinsic rate of 60-100 beats per minute.

  • >100 bpm indicates sinus tachycardia.

  • <60 bpm indicates sinus bradycardia.

• The atrioventricular (AV) node acts as a gatekeeper, pausing the electrical signal to allow for atrial and ventricular expansion and filling.

• The PR interval represents the time for expansion in the atria and ventricle, facilitating filling.

• The left ventricle has more Purkinje fibers due to its larger workload of pushing blood out through the aorta for systemic circulation.

Cardiac Cycle

• The cardiac cycle explained:

  • SA node fires.

  • PR interval: atria expand.

  • QRS complex: ventricles contract.

  • T wave: repolarization.

• Systole is the contraction phase; diastole is the expansion and filling phase.

• Blood pressure readings are inverted: 120/80 means 120 measures the squeeze (systole), and 80 measures the expansion/filling (diastole).

Heart Structure

• The heart has three layers: endocardium (the layer you're seeing on the ECG), pericardium (sac around the heart), and myocardium (muscle).

• The myocardium requires oxygenated blood supplied by the coronary arteries to function properly.

• Coronary artery blockages (often due to buildup from fatty foods) lead to myocardial ischemia and heart attacks (STEMI).

• STEMI is indicated by changes in the ST segment on the ECG.

Role of Electrolytes

• Electrolytes (sodium, magnesium, calcium) are essential for repolarization.

• Abnormalities in electrolyte levels can cause T wave changes (e.g., peaked T waves in hyperkalemia, inverted or flattened T waves).

Understanding ECG Components

• The relationship between ECG components and heart function: "Fire. Expand. Squeeze. Repolarize."

• Conduction Pathway of the heart consists of SA node -> AV node -> Bundle of His -> Purkinje Fibers.

• A first-degree heart block occurs when conduction from the SA to AV node is slowed, prolonging the PR interval.

Narrow vs. Wide QRS Complexes

• The width of the QRS complex indicates the origin of the electrical signal. You must only look at that space and not the entire complex.

  • Narrow QRS: signal originated in the atria (above the ventricles).

  • Wide QRS: signal originated in the ventricles or traveled through an abnormal pathway.

• Premature atrial contractions (PACs) are early beats that originate in the atria but may not perfuse (squeeze the ventricles).

• Premature ventricular contractions (PVCs) are early beats that originate in the ventricles and are wide and bizarre in appearance.

  • PAC: P wave fires, but ventricles don't squeeze; upright P wave.

  • PVC: Fired, didn't actually squeeze; wide and bizarre.

• The junction is near the Av node.

• Left and right bundle branch blocks affect the electrical pathway and result in wider QRS complexes.

  • These are electricity traveling down those paths

• For a rhythm to be considered sinus, it must have a P wave that is rounded and upright, and it must be regular.

Simplified Approach to Rhythm Interpretation

• Simplify rhythm analysis by categorizing rhythms based on QRS width and heart rate:

  • Wide and fast: ventricular tachycardia (V-tach) or Torsades de pointes; deadly rhythms.

  • Narrow and fast: supraventricular tachycardia (SVT), atrial flutter, atrial fibrillation with rapid ventricular response (RVR), junctional tachycardia, sinus tachycardia.

  • Slow rhythms: sinus bradycardia, idioventricular rhythm, junctional rhythm.

Rhythm Categories

• The table below summarizes the categorization of heart rhythms:

Tips for Identifying P Waves

• During rapid heart rates, it can be challenging to differentiate P waves from T waves.

• Start with the R wave and trace backward to identify the P wave; this can help distinguish it from the T wave.

• Tracing it backwards is a huge help!

Distinguishing A-Fib from SVT

• Varying heights (amplitudes) of the R waves suggest atrial fibrillation (irregular atrial activity).

• Clean, uniform R waves are more indicative of SVT (organized, regular rhythm).

• Use the approach of starting with 5 options and ruling out, rather than starting the differentials of 27 different diagnoses.

Application and Practice

• To interpret ECG strips: Determine if the patient is about to die, and look at the ECG to asses if it is wide and slow, wide and fast, narrow and slow, or narrow and fast, THEN determine what it qualifies as.

• Analyze practice ECG strips using the simplified approach.

  • Example 1: Narrow and slow with P waves = sinus bradycardia.

  • Example 2: Narrow and slow without P waves = junctional rhythm.

• Avoid memorizing 27 different rules and, instead, focus on the important qualities and the smaller set of options.

Additional Notes

• When something is blocked completely, it is wide because it takes longer to get there.

• It is better to assess a few different options rather than brain dumping all 27 possible options.

• Accelerated junctional is literally at 60 bpm, so one would likely think slow.

Extra Rhythms

• Ectopic atrial Rhythm

• MAT - Multifocal Atrial Tachycardia: Rate is > 100 bpm

• WAP - Wandering Atrial Pacemaker: Rate is < 100 bpm