Electrocardiogram (ECG) and Electrical Axis

• The provided text covers electrocardiograms (ECG), precordial leads and arterial pulse and other practical physiology topics.

Electrocardiogram (ECG) Introduction

• An electrocardiogram (ECG) records the electrical activity of the heart by placing electrodes on the body.
• The placement of electrodes (leads) and their distance from the heart influence the ECG interpretation.
• ECGs provide an approximate representation of electrical activity due to imperfect body conductivity and electrode adherence.
• ECGs can help calculate parameters like the electrical axis and heart rotation, in addition to providing information on the electrical activity of the heart.

Electrical Axis

• The heart's electrical activity, or fiber depolarization, follows a direction from atria to ventricles, which can be defined as the ELECTRICAL AXIS.
• Ventricles make up most of the cardiac mass; QRS complexes reflect ventricular depolarization.
• The electrical axis deviates leftward due to the larger size of the left ventricle.
• The direction of the electrical axis can be determined by placing electrodes according to Einthoven's triangle and recording bipolar distal leads (DI, DII, and DIII).
• The electrical axis can be calculated using the magnitude of the QRS complex in DI and DIII since the ventricles represent most of the electrical activity.

ECG in Different Conditions

• Respiration and body position changes can alter ECG records by affecting heart rate and rhythms.
• These changes are measured in an ECG using lead II (DII).

Action Potential (APUNTS)

• Action Potential: Initially, the cell surface is positive, but becomes negatively charged as Na+ enters. Finally, K+ channels open, K+ exits, and the surface returns to a positive charge
• Current: Generated when there's a charge difference on the cell surface.
• Electrode:
• Indifferent (base) electrode: the reference point.
• Exploring electrode: Varies.
• Positive environment: needle points upward.
• Negative environment: needle points downward.
• Resting state: continuous line due to no potential difference.
• Depolarization: sodium (Na+) influx creates a charge difference and current.
• Repolarization: potassium (K+) efflux creates a current in the opposite direction; returns to the initial isoelectric line.
• Depolarization Dipole: Changes the environment from positive to negative.
• Repolarization Dipole: Equivalent to depolarization but with reversed charges.

Auricular and Ventricular Depolarization/Repolarization

• Auricular depolarization: Occurring at the pacemaker, the first area where sodium ions will enter cells, creating an electronegative site, propagates across the atria.
• Ventricular depolarization: Series of electrical fields and sequence; initial depolarization in the septum (left to right) forms vector 1. Purkinje fibers trigger ventricular depolarization.
• Ventricular depolarization results in left ventricle taking longer to fully depolarize.
• Auricular repolarization: Not typically recorded.
• Ventricular repolarization: Is recorded and represented via vectors; indicates the areas that spend the longest time in negative charge.

ECG Recording Elements

• P Wave: Atrial depolarization
• QRS: Ventricular depolarization
• Q: Negative wave before R
• R: Any positive wave in QRS
• S: Negative wave after R (must be present when there is a greater net number of negative going waves before or after R)
• T: Ventricular repolarization
• Recording points/Leads are:
• R: right shoulder
• L: Left shoulder
• F: groin; the explorer electrode is L (the indifferent isn't considered).

Reading the ECG

• 1st Electrical Field (Atrial Depolarization): L is positive; needle points upwards
• 2nd Electrical Field: initial negative depolarization followed by significant positive electrical field
• Repolarization: T wave recorded in a positive deflection.
• Reading an ECG from the perspective of R results in the following
• 1st: P wave negative
• 2nd: QRS is positive followed by a larger negative
• 3rd: T wave is always positive unless in the situation it would otherwise be negative.

Bipolar Combination

• ECG readings are a combination of bipolar leads.
• D1 = Voltage amplitude in L minus Voltage amplitude in R
• D2 = Explorer in F – Explorer in R
• D3 = aVF - aVL D2 = D1 + D3

ECG results

• The electrical axis aids diagnoses for hypertrophy.
• Electrical axis abnormalities can indicate conduction issues.

Determining Positivity by Lead

• To diagnose it is necessary to locate the R wave in each derivation and verify its relationship to the deflection direction
• Check if R is always positive.

Derivation Voltages

• Note max Q, R, and S wave voltages for DI and DIII; maintain polarity and sum.
• Note only the waves you can identify, as QRS waves don't always appear.

Heart actions

• Heart activity can be reported using BMP and ΔΤ calculations
• To calculate the values of the expirations, take a cycle prior to an F9 marking
• Locate and Measure Q, T intervals during rest vs exercise
• Reference the graphs to identify

ECG Questions

• What does an ECG Measure
• An ECG represents the electrical processes that occur during heartbeats.
• What is the Einthoven law
• The triangle consists of the right shoulder (R), left shoulder (L), and groin (F)
• Bipolar leads: D1 (RL), D2 (FR), and D3 (LF).
• D2 = D1 + D3
• Information provided by electrical axis and factors affecting its orientation:
• The axis gives angle of the heart. Factors include height, chest space, age, hypertrophy, and conduction blocks.
• Factors affecting the R wave's amplitude in leads:
• Cardiac mass affects amplitude. Comparison is best between individuals using the same lead types.
• Heart rates in different situations.

Respiratory cycles.

• Frequency increases when seated versus lying down
• Gravity limits heart work in seated position so baroreceptors elevate HR)
• Resting pulse: 60-70 bpm
• Exercise BPM: 120-160 bpm (depends on effort).
• Cycle of respiratory system and steps:
• Inspiration: Increased rate (active). Increased sympathetic input raises rate; pressure reduction as chest cavity expands.
• Negative pressure in vessels impacts vein return and cardiac output and increases BPM. Capillaries show 25mmHg
• Expiration: passive process

Cardiac conditions

• Exercises resulting in shorter ventricular diastole reduces ventricle fill time and reduces time between cycles
• An ECG isn't dependent on all waves, results still may be valid if that is the case.
• The P wave should be present.

ECG and Pathologies

• Isoelectric ST segments indicate ST is typically isoelectric
• The recording should not display noise, as flat lines are not normal.

PRÁCTICA 2: PRECORDIAL LEADS AND ARTERIAL PULSE

• Second practice exercise discusses precordial leads, arterial pulses and their properties.

Precordial Lead introduction

• Precordial leads record local cardiac electrical activity, unlike distal leads which measure global activity.
• Precordial leads are unipolar
• Six electrodes measuring the QRS complex in relation to heart base/tip proximity are placed.
• This ECG helps in determining cardiac rotation.

Arterial Pulse

• Ventricles can produce pressure waves from blood volume increase passed through veins/arteries.
• Volume is controlled by nervous system, temperature, emotions, posture, metabolic activity.
• Blood volume changes are measured via plethysmograph with phototransducer and light absorption.
• An ECG with Bipolar distal DII measures arterial pulse volume changes during physiological/experimental conditions.

Exercises

• Amplitude changes exist in the precordials because electrical activity will appear differently based off the observation point.
• Pre cordial deviations help isolate heart tissue and injuries on the heart
• ECG measures QRS activity, pulse rate measures pulse

Experiment set-up

• The QRS complex is rarely changed as it's derivation based.
• The pulse depends on the location it's measured
• Blood flow restrictions will impact QRS values
• Heat causes vasodilation impacting the wave amplitude and cold causes the opposite
• Gravity will impact pulse rate and amplitude.

PRÁCTICA 3: EXCITACIÓ I ACOPLAMENT CARDÍACS (Action Potential)

• The following are some notes related to action potential

Action potential and stimulus Amplitude

• 15.5 μA stimulus is required to initiate an action potential.
• -55 mV is the threshold voltage for Na+ influx.
• A higher stimulus amplitude reduces the time to peak as the membrane potential can rapidly reach threshold.
• A higher stimulus amplitude slightly increases peak due to increased Na+ conductance.

Na, K+ ion concentrations and Action potential

• Action potential peak is decreased by 4mV with lower Na+ influx at 100 mM Na+ concentration.
• Na influx becomes slower shifting potential upwards if Na Gradient isn't as large
• Hyperkalemia ([K+]o > 5 mM) will lead to resting potential depolarization, in turn hyperpolarizing the Na+.
• Chronic depolarization reduces Na+ current/conduction velocity.
• Hypokalemia: Decreased extracellular potassium hyperpolarizes the resting potential requiring a stronger stimulus.

Refractory Status

• INa of 2nd pulse cannot activate with interval duration at or below 200ms
• Na inactivation gate shuts off Na flow, inactivating its excitability until late phase 3 causing this.
• Cardiac tissue cannot conduct a second action potential without restored Na excitability at the end of phase 3.
• Recovery from inactivation requires 10ms at -100mV, 30ms at -80mV or 100ms at -72mV
• Prevents repeated heart re-excitation that impacts ventricular blood fill.

Key Action Potential Measurements

• Effective Refractory Period (ERP): from 250-300ms; cells are excitable to physiological stimuli following action potential upstroke; stimulation yields no new action potentials.
• Relative Refractory Period (RRP): 50ms conduction occurs, but velocity is limited.
• After ERP all Na channels have returned to their starting state making velocity maximal, beats in RRP have limited velocity producing QRS.

Premature action potential

• The greater the depolarization, the greater the number of channels that move into an unexcitable phase.
• Drugs like tetrodotoxin (TTX) prolong AP.

AP Conduction Velocity

• Ion channel conductance is the flow of ions through a channel and is based on the electrochemical driving force.
• G (Siemens) = I (Ampere) / V (milliVolts)
• Reduced sodium conductance leads to the slowing of action potential construction.

Action potential currents

• The cardiac Na current drives conduction rate.
• Smaller inward Na currents result in longer times for reaching action potential (AP) thresholds because V=IR → I= V/R and G=1/R therefore I= VG
• Net Driving Force(mV)=Em+(-ENa) where Ohms Law is
• INa=gNa(Em-ENa)

Repolarization role of Potassium

• IKr = delayed outward rectifier current and is mediated by the HERG channel which is needed for ventricular repolarization. This impacts the AP duration increasing/decreasing its overall value

Systema Respiratori

• A number of factors that can impact volumes and capacities of the respiratory system

Introductory Details

• Patients breathing volumes can be measured with an instrument called the espirómetro
• The device is able to display both flux and Volumes of airflow
• Exact results require an exact process for recording, to give the best volume and flux estimates

Key Steps

• A person may inspire and exipire multiple times to reach a number of conditions
• Volume and Capacity are measured to study respiratory conditions

Diseases

• Volumes and capacities can change when functional spaces are impacted

Definitions

• Below are calculations to measure volume of breathing based off height and gender
• CV = 0.052A - 0.022E-3.60 for males
• CV: Vital Capacity in liters | A: Height (in cm) | E: Age
• CV = 0.041A-0.018E - 2.69 for females

Measuring Fluidity in lungs

• In addition to capacity and volume, a study of the fluidity can tell the apparati health.
• Obstructions can impact individuals, leading to a limited capability of mobility in air.

Common Terms

• Forced Expiratory volumes measure how a VC is lost when breathing.
• Volumetric Ventilation test shows how capacity if ventilatory can be reduced

Important to note that

• The following can be used to estimate patient state:
• An adult can exhale 66-83% of volume in one second.
• Can exhale 75 - 95% in the second seconds.
• Can lose 78 to 97% of this capacity at the third second, if there is proper function
• People can have asthma if they are unable to maintain these values. Restrictive lung function will limit this. Ventilation:
• Maximum can measure the air moved though the lung during hyperventilation
• Limited by musculature or restrictions
• Restrictive and obstructive ailments will lead to reduction

Lungs

• There are a number of factors that impact the use of lungs
• Height varies because of the size of the chest
• Factors impacting lungs are weight, physical state
• VRE and VRI would be diminished by faster erythrocites as well from more intense exercise.

Define terms

• Volumes versus Capacities is about sums of the individual

Volumen Tidal definition

• Inspiratory or expiratorial cycle depending on the volume (0.5 - 1L)
• Defined Volumen Tidal: volume that can be filled between a normal inspiration and maximal is called Lumen de Reserva
• Defined Volumen de Reserva Espiratorio: This addition volume may also Expire and may increase it's maximal
• Volumen Residual: amount left after maximal experience
• Pulmonary Capacity: Liters for maximum expansion of lung
• Pulmonary Capacities are: inspiratoria, espiratoria, vital, pulmonar total and residual
• Defined Volumen espiratorio forzado : percentage that can expire, related to disease.
• Ventilación Voluntaria Máxima is indici for muscles of breathing, -MVV falls due to less elasticity in pulmonaries.

Asthmatics and Lung functionality

• Lesion will impact the FEV.
• Smooth Muscle count, thickening.