Cardiac_Dysrhythmias_lecture_notes

## Pumping Action of the Heart - Accomplished by rhythmic relaxation and contraction of muscular walls of two atria and two ventricles. - **Diastole**: All four chambers relax simultaneously, allowing atria and ventricles to fill for contraction. Commonly referred to as ventricular filling. - **Systole**: Refers to contraction of atria and ventricles. - **Atrial Systole**: Occurs first, during the end of ventricular diastole. - **Ventricular Systole**: Follows atrial systole, allowing ventricles to fill completely before blood ejection. - This synchronization is termed **atrial kick**, adding 20-30% volume to ventricles. ## Blood Flow in the Heart - **Right Side of the Heart**: Distributes venous blood to lungs via pulmonary circulation for oxygenation. - **Left Atrium**: Receives oxygenated blood from pulmonary circulation. - **Left Side of the Heart**: Distributes oxygenated blood to the body via the aorta (systemic circulation). ### Coronary Arteries - Originate from the aorta above aortic valve leaflets, supplying blood to the heart. - Unlike other arteries, coronary arteries are perfused during diastole. - In tachycardic rhythms (HR > 100), diastolic time is shortened, risking myocardial perfusion and ischemia, particularly patients with CAD. ### Left Coronary Artery Branches - **Left Main Coronary Artery**: - **Left Anterior Descending Artery**: Supplies anterior 2/3 of septum, anterior & apical LV, parts of RV. - **Circumflex Artery**: Supplies LA, lateral LV, and sometimes posterior LV & septum; nourishes 40% of SA Node, 10% of AV Node. - **Right Coronary Artery (RCA)**: - Supplies RA, RV, inferior/posterior LV, and posterior wall of heart (via posterior descending artery). - Contributes significantly to supply of AV Node and Bundle of His. ## Cardiac Conduction System - Generates/transmits electrical impulses, stimulating myocardial contraction. - **SA Node**: Primary pacemaker (60-100 impulses/minute). - Located at junction of superior vena cava and right atrium; initiates impulse transmitted through atrial cells. - **AV Node**: Secondary pacemaker (40-60 impulses/minute); coordinates impulses between atria and ventricles. - **Bundle of His**: Divides into right/left bundle branches, ensuring impulses reach ventricles for contraction. ### Autonomic Nervous System Effects - Heart rate influenced by sympathetic (accelerates HR) and parasympathetic fibers (decreases HR). - **Sympathetic Activation**: Increases heart rate, force of contraction, and peripheral resistance (blood pressure). - **Parasympathetic Activation**: Decreases heart rate and conduction; vagus nerve stimulation reduces HR but has no effect on ventricles. ## Electrocardiogram (ECG) Basics - **ECG Tracing**: Reflects electrical forces of heart; P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization). - Lead placement is critical for accurate ECG readings. - Each lead records electrical activity between two electrodes, determining direction and magnitude of depolarization and repolarization waves. ## Cardiac Cycle Components - **P Wave**: Represents atrial depolarization; normal <2.5 mm height, <0.11 sec duration. - **QRS Complex**: Ventricular depolarization; typically <0.12 sec (<3 little boxes). Includes: - Q Wave: First negative deflection post-P wave (<0.04 sec). - R Wave: First positive deflection post-P wave. - S Wave: First negative deflection post-R wave. - **T Wave**: Represents ventricular repolarization; similar direction to QRS. - **PR Interval**: Time from start of P wave to start of QRS (0.12-0.20 sec in adults). - **ST Segment**: Between end of QRS and start of T wave; analyzed for signs of cardiac ischemia. - **QT Interval**: Total time for ventricular depolarization/repolarization; varies with HR, typically 0.32-0.40 sec. ## Rhythm Identification and Interpretation - Heart rhythm (regular/irregular) assessed through measurement of intervals and morphology: - **Rate Calculation**: Via 6-sec ECG strip multiplication or counting small boxes between R waves. - Regular rhythm: Count QRS complexes in 6 sec and multiply by 10. - Rhythm interpretation includes rate, rhythm regularity, PR intervals, QRS analysis, and patient assessment for stability. ## Dysrhythmias Overview - Dysrhythmias: Disorders of electrical impulse formation/conduction in the heart. - Can result in altered heart rate/rhythm and symptomatic effects depending on type and severity. - **Normal Sinus Rhythm**: Characterized by rates of 60-100 bpm, regular rhythm, and consistent P waves - Treatment: Monitor, verify pulse. - **Sinus Arrhythmia**: Irregular rhythm that varies with respiration; common in athletes/children. - Treatment: Monitor; usually not treated unless symptomatic. - **Sinus Bradycardia**: Rate <60 bpm; associated with vagal stimulation or medications. - Treatment: Atropine, dopamine, transcutaneous pacing if symptomatic. - **Sinus Tachycardia**: Rate >100 bpm; often compensatory for need (e.g., pain, hypoxia). - Treatment: Identify cause; beta-blockers or possibly cardioversion if persistent. ## Other Dysrhythmias and Management Strategies - **Atrial Fibrillation**: Highly irregular rhythm; atrial rate of 300-600 bpm; risks of stroke and heart failure management. - Treatment: Rate/rhythm control, anticoagulants, possible cardioversion. - **Ventricular Tachycardia (VT)**: Defined as three or more PVCs in a row; can be symptomatic or stable/unstable. - Treatment: Antiarhythmic medications, cardioversion if symptomatic. - **Asystole**: Absence of electrical activity; requires immediate CPR and identification of underlying causes. - **Pulseless Electrical Activity (PEA)**: Electrical rhythm without pulse; management focuses on CPR and identifying reversible causes.

Pumping Action of the Heart

• The heart functions as a muscular pump through rhythmic relaxation and contraction cycles of two atria and two ventricles, optimizing blood flow throughout the body.

• Diastole: During this phase, all four chambers of the heart relax simultaneously, allowing both the atria and ventricles to fill with blood in preparation for the subsequent contraction. This phase is crucial as it is often referred to as ventricular filling, where passive blood flow occurs from the atria into the ventricles.

• Systole: This phase refers to the contraction of both the atria and ventricles, vital for pumping blood out of the heart.

• Atrial Systole: Occurs at the end of ventricular diastole, pushing additional blood into the ventricles. This action ensures the ventricles are adequately filled.

• Ventricular Systole: This phase follows atrial systole and is essential for ejecting blood from the ventricles into the pulmonary artery and aorta. Before this occurs, the ventricles must fill completely, which is aided by the synchronized contraction that is termed atrial kick, contributing an additional 20-30% of the ventricular volume.

Blood Flow in the Heart

• Right Side of the Heart: This side is responsible for receiving deoxygenated blood from the body and distributing it to the lungs via pulmonary circulation, where carbon dioxide is exchanged for oxygen.

• Left Atrium: After oxygenation in the lungs, oxygenated blood returns to the left atrium via the pulmonary veins.

• Left Side of the Heart: This side subsequently distributes oxygen-rich blood to the body through the aorta, representing systemic circulation crucial for supplying organs and tissues with oxygen and nutrients.

Coronary Arteries

• The coronary arteries, which originate from the aorta above the aortic valve leaflets, are vital in supplying blood to the heart muscle itself.

• Unlike other arteries in the body, the coronary arteries are primarily perfused during diastole, highlighting the importance of this phase in maintaining myocardial health.

• In cases of tachycardic rhythms (heart rate greater than 100 bpm), the duration of diastole is shortened, potentially jeopardizing myocardial perfusion and leading to ischemia, especially in patients with coronary artery disease (CAD).

Left Coronary Artery Branches

• Left Main Coronary Artery:

  • Left Anterior Descending Artery (LAD): Supplies the anterior two-thirds of the septum, as well as the anterior and apical regions of the left ventricle (LV), and parts of the right ventricle (RV).

  • Circumflex Artery: Supplies blood to the left atrium (LA) and the lateral and sometimes posterior walls of the left ventricle, nourishing 40% of the sinoatrial (SA) node and 10% of the atrioventricular (AV) node.

• Right Coronary Artery (RCA):

  • This artery supplies the right atrium (RA), right ventricle (RV), the inferior and posterior walls of the left ventricle, and the posterior wall of the heart, with significant contributions to the blood supply of the AV node and the Bundle of His, thereby facilitating electrical conduction and coordination within the heart.

Cardiac Conduction System

• The cardiac conduction system is crucial for generating and transmitting electrical impulses, thereby stimulating myocardial contraction in a coordinated manner.

• SA Node: Known as the primary pacemaker of the heart, firing at a rate of 60-100 impulses per minute, it is located at the junction of the superior vena cava and right atrium. This node initiates impulses that are transmitted through atrial cells, facilitating atrial contraction.

• AV Node: Acts as a secondary pacemaker with a firing rate of 40-60 impulses per minute, playing a significant role in coordinating impulses between the atria and ventricles, ensuring optimal timing for contraction.

• Bundle of His: This conductive pathway divides into right and left bundle branches, ensuring that the electrical impulses reach the ventricles promptly, allowing for effective contraction and blood ejection.

Autonomic Nervous System Effects

• Heart rate and contractility are influenced by both branches of the autonomic nervous system:

• Sympathetic Activation: Increases heart rate, the force of myocardial contraction, and peripheral resistance, ultimately raising blood pressure. This effect is crucial in fight or flight situations.

• Parasympathetic Activation: This component decreases heart rate and conduction velocity. Stimulation of the vagus nerve reduces the heart rate without affecting ventricular contractility, promoting a state of relaxation.

Electrocardiogram (ECG) Basics

• ECG Tracing: Records the electrical forces exerted by the heart; consists of key phases:

  • P Wave: Signifies atrial depolarization; normal heart rate around 100 bpm often compensatory in response to physiological needs such as pain or hypoxia.

  • QRS Complex: Represents ventricular depolarization, crucial for the contraction phase.

  • T Wave: Indicates ventricular repolarization, marking the end of one cardiac cycle and preparation for the next.

• Proper lead placement is critical for obtaining accurate ECG readings, as each lead records electrical activity between two electrodes, which helps determine the direction and magnitude of depolarization and repolarization waves.

Cardiac Cycle Components

• P Wave: Represents atrial depolarization, indicating effective filling of the ventricles; it is normal to have heart rates around 100 bpm, with adjustments based on bodily requirements.

• Management Strategies: In cases of abnormal P waves, the focus should be on identifying the underlying cause, potentially utilizing medications such as beta-blockers or considering cardioversion if the irregularity is persistent.

Other Dysrhythmias and Management Strategies

• Atrial Fibrillation: Characterized by a highly irregular rhythm and atrial rates that can range from 300-600 bpm, this dysrhythmia significantly increases the risk of stroke and heart failure.

  • Management: Involves both rate and rhythm control techniques, the use of anticoagulants to mitigate stroke risk, and the possibility of cardioversion to restore normal rhythm.

• Ventricular Tachycardia (VT): Defined as three or more premature ventricular contractions (PVCs) in succession, this condition may present as symptomatic or remain stable/unstable.

  • Management: Typically involves the administration of antiarrhythmic medications and possible cardioversion if the patient exhibits symptoms.

• Asystole: This life-threatening condition reflects an absence of electrical activity in the heart, necessitating immediate CPR and identification of underlying causes to restore cardiac function.

• Pulseless Electrical Activity (PEA): This phenomenon exhibits an electrical rhythm without a detectable pulse; management focuses on immediate CPR and identifying reversible causes to restore circulation.

Emergency Treatment of Lethal or Unstable Dysrhythmias

Lethal Cardiac Rhythms

Ventricular Fibrillation or Pulseless Ventricular Tachycardia

• CPR/Defibrillation as soon as defibrillator available

  • Manual biphasic defibrillator: typically start with 120-200 joules

  • Monophasic defibrillator: start with 360 joules

  • AED: device specific; follow voice prompts

• Secure airway and confirm placement of airway devices; give 100% oxygen

• Epinephrine 1 mg. IV/IO (Intraosseous); repeat every 3-5 minutes

• Amiodarone 300 mg. IV/IO; may give additional 150 mg. once followed by IV infusion if successful for ventricular rhythm control to max dose of 2.2 Grams/24 hours

• Lidocaine 1-1.5 mg/kg. IV/IO; may give additional 0.5-0.75 mg/kg. once followed by IV infusion if successful for ventricular rhythm control to max dose of 2.2 Grams/24 hours

• Magnesium IV if torsades de pointes

During CPR:

• Push hard and fast (100-120 compressions/minute)

• Ensure full chest recoil between compressions

• Minimize interruptions in chest compressions

• Rotate compressors every 2 minutes with rhythm and pulse check

Pulseless Electrical Activity

• CPR

• Secure airway; give 100% oxygen

• Epinephrine (as in VF/pulseless VT)

• Treat underlying causes (see below)

Asystole

• CPR

• Secure airway; give 100% oxygen

• Epinephrine (as in VF/pulseless VT)

• Treat underlying causes (see below)

Reversible Causes (Hs & Ts)

• Hypovolemia

• Hypoxia

• Hydrogen Ion (acidosis)

• Hypo/hyperkalemia

• Hypothermia

• Tension pneumothorax

• Tamponade, cardiac

• Toxins

• Thrombosis, pulmonary

• Thrombosis, coronary

Serious Rapid Supraventricular Electrical Conduction Abnormalities

Rapid Atrial Fibrillation/Flutter

• Ensure patent airway; give 100% oxygen

• Diltiazem, beta-blocker, or digoxin for rate control

• Synchronized cardioversion

Supraventricular Tachycardia (SVT)

• Ensure patent airway; give 100% oxygen

• Valsalva or other vagal maneuvers

• Adenosine 6 mg. rapid IV push

• Second dose: 12 mg rapid IV push

• Synchronized cardioversion

Emergency Treatment of Serious Ventricular Electrical Conduction Abnormalities

Ventricular Tachycardia with a Pulse

• Ensure patent airway; give 100% oxygen

• Amiodarone 150 mg. IVP over 10 minutes; repeat as needed if VT recurs

• Consider Procainamide 20-50 mg/min IV until arrhythmia is suppressed, hypotension ensues, QRS duration increases > 50%, or a maximum of 17 mg/kg given. Avoid if prolonged QT or CHF

• Consider Sotalol 100 mg (1.5 mg/kg) over 5 minutes – avoid if prolonged QT

• Consider Adenosine 6/12mg if SVT with aberrance suspected

• Synchronized cardioversion if unstable

Premature Ventricular Contractions (PVCs)

• If patient is symptomatic:

  • Ensure patent airway and adequate oxygenation

  • Amiodarone or Procainamide IV

  • Look for causes

Heart Blocks/Sinus Bradycardia

First Degree Heart Block (AV Block)

• Monitor patient

Sinus Brady/2nd Degree Heart Block (Type I & II) & 3rd Degree (Complete) Heart Block

• Monitor (if adequate perfusion or patient asymptomatic)

• If patient symptomatic with poor perfusion (altered mental status, chest pain, low BP, etc.):

  • Ensure adequate airway and give 100% oxygen

  • Atropine 1 mg. IV push; may repeat to total dose of 3 mg.

  • Epinephrine IV infusion or dopamine IV infusion

  • Pace (transcutaneous, transvenous, epicardial)

Types of Electrical Activities

Proceed to synchronized cardioversion or pacing when unstable (altered mental status, chest pain, low BP or other signs of shock); consider sedation prior to the procedure to ensure patient comfort and minimize anxiety. In cases of persistent dysrhythmias, continuous monitoring is essential to assess the effectiveness of the intervention and to identify any potential complications that may arise during treatment.