more ACLS notes

Third Degree Heart Block vs. Mobitz II

• Distinguishing Third Degree Heart Block from Mobitz II:

  • In a third-degree heart block, there's no communication between the P waves and QRS complexes.

  • It's crucial to assess whether the PR interval varies.

  • If the PR interval remains constant, the likelihood of it being a third-degree block is very low.

  • If the PR interval is constant, it is more likely a Mobitz II second-degree block.

• Mobitz II Characteristics (Second Degree Type II):

  • Some P waves are not followed by a QRS complex.

  • Example: One QRS gets through, then two don't, then one gets through, then two don't.

• QRS Complex Width in Third Degree Heart Block:

  • A third-degree heart block can present with a narrow QRS complex.

  • This indicates that the impulse is generated in the AV node.

  • The block occurs around the northern part of the AV node.

  • The Bundle of His can still fire, resulting in a narrow QRS.

Acute Coronary Syndromes (ACS)

• ACS Overview:

  • ACS can occur due to coronary atherosclerosis and plaque formation.

  • Two main types of ACS are:

    • Non-ST segment elevation ACS (NSTE-ACS).

    • ST segment elevation myocardial infarction (STEMI).

  • STEMI is generally more serious.

    • Develops after a plaque rupture or erosion leading to a blood clot that occludes a coronary artery.

  • Both can lead to sudden cardiac arrest and death.

    • Approximately half of deaths occur outside the hospital.

• Importance of Early Recognition and Rapid Response:

  • Strong public education.

  • PAD programs.

  • STEMI systems of care.

• STEMI Chain of Survival:

  • Emergency Medical Services (EMS) and hospital personnel play a critical role.

    • Recognizing and treating the underlying causes of ACS.

Heart Disease Statistics and Terminology

• Heart Disease as Leading Cause of Death:

  • Heart disease is the leading cause of death in the US.

  • Cardiac-related issues are statistically the most likely cause of death when encountering a deceased individual.

• Thrombus as a Potential Cause of Cardiac Arrest:

  • When considering H's and T's, thrombus (specifically coronary thrombus) is a high probability reason for cardiac arrest.

• Heart Attack vs. Myocardial Infarction (MI):

  • Heart attack and myocardial infarction (MI) are synonymous.

  • Use "heart attack" when communicating with the public.

  • Use "MI" in EMS or medical settings.

Cardiac Cycle: Systole and Diastole

• Diastole: Ventricles are Filling

  • Atria are refilling

• Systole: Ventricles are Squeezing

  • Blood is pushed towards the pulmonary artery and aorta

• Blood Pressure Correlation:

  • Systole is represented by the higher number in blood pressure.

  • Diastole is represented by the lower number.

• Systole:

  • Ventricles (left and right) are the main actors.

  • Tricuspid and mitral valves are closed.

  • Blood is pushed towards the pulmonary artery (deoxygenated blood to the lungs) and the aorta (oxygenated blood to the body).

• Diastole:

  • Blood is filling the ventricles.

  • Tricuspid and mitral valves are open.

  • Aortic valve (to the body) and pulmonic valve (to the lungs) are closed.

• ECG Representation of Diastole:

  • P wave is associated with diastole.

  • P wave corresponds to the atrial kick, pushing the last bit of blood into the ventricles.

• Value of Overfilling the Ventricles During Diastole:

  • Overfilling allows for a more forceful contraction (Starling's Law).

  • Starling's Law: As cardiac muscle fibers stretch, the force of contraction increases.

Ejection Fraction (EF) and Cardiac Output (CO)

• Ejection Fraction (EF):

  • Definition: The percentage of blood expelled from the ventricle with each contraction.

  • Normal EF: 55-70 \%. 70 is considered great

  • Low EF: Indicates potential heart failure.

• Cardiac Output (CO):

  • Definition: The amount of blood pumped by the heart per minute.

  • Determined by: Stroke volume and heart rate.

    • CO = Stroke Volume \times Heart Rate

  • Stroke volume is related to ejection fraction.

• Heart Failure and Cardiac Output:

  • Poor cardiac output is related to heart failure.

Preload and Afterload

• Preload:

  • Definition: The amount of blood returning to the heart (atria).

  • Drugs that reduce preload:

    • Nitroglycerin

    • Morphine

    • Anything that drops blood pressure will also reduce preload.

• Afterload:

  • Definition: The resistance the heart must overcome to eject blood into circulation.

  • Vasoconstriction increases afterload.

  • Drugs that increase afterload:

    • Norepinephrine

    • Epinephrine

    • Dopamine

Coronary Artery Blood Supply and Significance

• Coronary Artery Blood Supply Timing:

  • Coronary arteries receive blood flow during diastole, not systole.

  • During systole, the leaflets cover over coronary artery entrances.

  • During diastole, blood starts to backflow, closing the leaflets and opening the entrance to the coronary arteries.

• Key Coronary Arteries:

  • Right Coronary Artery (RCA).

  • Left Coronary Artery (LCA).

• Right Coronary Artery (RCA):

  • Feeds the inferior part of the left ventricle.

  • Also feeds the posterior wall of the left ventricle.

  • Feeds the right ventricle.

  • If a patient is having an inferior MI, consider the possibility of the right ventricle and posterior also being affected.

  • SA Node Supply:

    • Supplies the SA node in about 50% of the population.

  • AV Node Supply:

    • Almost exclusively feeds the AV node.

    • A blocked RCA can cause an irritable AV node, potentially leading to AV blocks.

• Clinical Correlation:

  • If a patient presents with an inferior MI, they may also have an AV block.

  • If a patient presents with a second-degree AV block, assess for a STEMI.

• Treatment Considerations for AV Block:

  • Address any bradycardia affecting perfusion.

    • Atropine, pacing, epinephrine, or dopamine can be used to address bradycardia.

  • Address STEMI, if present.

• Inferior MI Involvement:

  • About 50% of inferior MI cases also involve the posterior and/or right ventricle.

    • Relevant for treatment strategies.

• Left Coronary Artery (LCA):

  • LAD (Left Anterior Descending):

    • Feeds the anterior wall of the left ventricle.

    • Often called the 'widowmaker' due to high risk of sudden cardiac death with full blockage.

    • Also feeds the right and left bundle branches.

      • Blockage can cause a bundle branch block.

  • LCX (Left Circumflex Artery):

    • Feeds the lateral and some posterior parts of the left ventricle.

    • May also feed the SA node in some individuals.

• New Left Bundle Branch Block:

  • A new left bundle branch block in a patient with chest pain is an indication for the cath lab.

    • The patient may say they don't know what that means or say they have never heard of it before.

Arrhythmias Due to Blockages

• SA Node Blockage:

  • Can lead to sinus pauses or junctional escape rhythms.

Collateral Circulation

• In some individuals, the heart may develop collateral circulation.

  • Vessels expand to feed areas not getting enough blood, compensating for poor vessels.

  • Develops over time.

Coronary Artery Disease (CAD) vs. Acute Coronary Syndrome (ACS)

• CAD (Coronary Artery Disease):

  • Atherosclerosis, plaque build-up over time.

  • Not necessarily acute.

• ACS (Acute Coronary Syndrome):

  • Acute onset of symptoms related to the heart.

  • Umbrella term including:

    • STEMI

    • NSTEMI

    • Unstable angina

• Ischemia:

  • Lack of blood supply to tissue, leading to a shortage of oxygen (O_2).

  • Can result from atherosclerosis or plaque rupture.

  • ECG: Potential T wave inversion.

• Injury:

  • Ischemia bad enough that cells begin to be damaged.

  • Anaerobic metabolism due to lack of oxygen, sodium-potassium pump starts to break down.

  • ECG: ST segment elevation.

• Infarction:

  • Injury leads to cell death.

  • Cardiac cells do not regenerate.

  • ECG: Pathological Q waves.

Cardiac Layers and ECG Changes

• Three Layers of the Heart:

  • Endocardium.

  • Myocardium.

  • Epicardium.

• ST Segment Elevation:

  • Usually indicates injury through all three layers of the heart.

Consequences of Ischemic Heart

• Cardiogenic shock:

  • Lack of strong heart beat leads to poor cardiac output.

  • Number one cause is MI.

• Dysrhythmias such as V Fib can occur due to irritability.

  • This occurs in about 55-60% of people.

Atherosclerosis and Plaque Formation

• Plaque Formation:

  • Narrows vessel reducing blood flow leading to 60% blockage

• Plaque Break Off:

  • Block smaller vessels.

• Exposure of collagen causes platelets to accumulate and creating a clot

Key Terms

• Stenosis: Narrowing of a vessel.

• Lesion: Abnormal change to tissue, often a clot.

• Catheterization (Cath):

  • Insertion of a wire into an artery (femoral or radial).

  • Diagnostic or interventional.

• Stress Test: Evaluation to identify potential blockages.

• Stent: Device to open a blocked vessel.

• CABG (Coronary Artery Bypass Graft):

  • Surgical procedure to reroute blood flow around blockages.

• Balloon Pump:

  • Not the same as a stent.

  • Big balloon that goes into your artery and inflates and deflates every single time your heart beats.