Chapter06

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Chapter 6 : 

Chapter 6 The Basic Beat

Basic Components : 

Basic Components Wave: Deflection from baseline that represents a cardiac event Segment: Specific portion of the complex as represented on ECG Interval: Distance, measured as time, between two cardiac events

Waves and the Baseline : 

Waves and the Baseline Waves are a deflection of the baseline. The baseline is a line from one TP segment to the next.

Wave Forms : 

Wave Forms Waves can be: Single Isolated Positive or negative deflections Biphasic deflections with both + and - components Combinations that have multiple + and - components

Wave Nomenclature : 

Wave Nomenclature Waves should be named according to: Size Location Direction of deflection

QRS Wave Nomenclature : 

QRS Wave Nomenclature Tall or deep waves in QRS complex are given capital letters: Q, R, S, R' Small waves are given lowercase letters: q, r, s, r'

X Prime : 

X Prime Changes occurring in QRS complexes can lead to bizarre complexes. Waves are named differently if they change directions and cross the baseline. This is called X' (X prime). X is not an actual wave, but a term that can stand for either an R or S wave. R' and S' (R prime and S prime) = extra waves within the QRS complex.

Q, R, and S : 

Q, R, and S Q wave First negative deflection after P wave R wave First positive deflection after P wave S wave First negative deflection after R wave If there is another upward component, we start with R'.

R' and S' Complexes : 

R' and S' Complexes

The P Wave (1 of 2) : 

The P Wave (1 of 2) Usually the first in the ECG complex Represents electrical depolarization of both atria Starts when the SA node fires Duration can vary between 0.08 and 0.11 seconds in adults Axis: Downward and to the left, 0º to +75º

The P Wave (2 of 2) : 

The P Wave (2 of 2)

The Tp Wave : 

The Tp Wave Represents repolarization of atria Deflects in the opposite direction of P wave Occurs at same time as QRS wave, so is not usually seen

The PR Segment : 

The PR Segment Time between end of P wave and beginning of QRS complex Usually found along baseline Anything >0.8 mm is pathological

The PR Interval (1 of 2) : 

The PR Interval (1 of 2) Represents: Impulse initiation Atrial depolarization Atrial repolarization AV node stimulation His bundle stimulation Bundle branch and Purkinje system stimulation

The PR Interval (2 of 2) : 

The PR Interval (2 of 2) From beginning of P wave to beginning of QRS complex Includes P wave and PR segment Normal duration: 0.12 to 0.20 sec

The QRS Complex (1 of 2) : 

The QRS Complex (1 of 2) Represents ventricular depolarization Main components are Q, R, and S waves Q wave can be present or absent. R wave: First positive deflection after P; will be initial wave of QRS complex if no Q is present. Normal duration: 0.06 to 0.11 sec Axis: -30 to +105, downward and to left

The QRS Complex (2 of 2) : 

The QRS Complex (2 of 2)

Q Wave Significance : 

Q Wave Significance Can be benign, or sign of dead myocardial tissue Significant Q wave Indication of MI over region involved 0.03 sec or wider Height equal to or greater than 1/3 height of R wave Insignificant Q wave Commonly found in I, aVL, and V6 Due to septal innervation (called septal Qs)

Insignificant Q Wave : 

Insignificant Q Wave

Significant Q Wave : 

Significant Q Wave

Intrinsicoid Deflection (1 of 2) : 

Intrinsicoid Deflection (1 of 2) Measured from beginning of QRS complex to beginning of negative downslope of R wave Represents amount of time for electrical impulse to travel from Purkinje system to epicardium under electrode Normal intrinsicoid deflection: Right precordials = 0.035 Left precordials = 0.045

Intrinsicoid Deflection (2 of 2) : 

Intrinsicoid Deflection (2 of 2)

The ST Segment : 

The ST Segment Represents electrically neutral period between ventricular depolarization and repolarization Segment from end of QRS complex to beginning of T wave Usually found along the baseline Point where ST segment begins is called the J point Axis: Inferior and to the left  Important: Any ST elevation in a symptomatic patient should be considered representative of myocardial injury or infarction

The J Point : 

The J Point

The T Wave (1 of 2) : 

The T Wave (1 of 2) Represents ventricular repolarization Is next deflection (+ or –) after ST segment Normal T wave: Begins in same direction as QRS complex Asymmetrical (first part rising/dropping slowly, latter part moving faster)

The T Wave (2 of 2) : 

The T Wave (2 of 2)

Assessing T Wave Symmetry : 

Assessing T Wave Symmetry

QT Interval (1 of 2) : 

QT Interval (1 of 2) Encompasses QRS complex, ST segment, T wave Represents all events of ventricular systole From beginning of ventricular depolarization to end of repolarization Normal duration is variable, but usually less than 1/2 of R-R interval Prolonged QT interval is a sign of possible life-threatening arrhythmias

QT Interval (2 of 2) : 

QT Interval (2 of 2)

QTc Interval (1 of 2) : 

QTc Interval (1 of 2) Stands for “QT corrected interval” As heart rate decreases, QT interval lengthens. As heart rate increases, QT interval shortens. By calculating QTc interval, it can be stated that normal is around 0.410 sec or 410 milliseconds. Formula: QTc = QT + 1.75 (ventricular rate – 60)  Cardiac events represented by QTc interval = all events of ventricular systole

U Wave : 

U Wave A small, flat wave sometimes seen after T wave and before next P wave. No one knows for sure what it represents. Important: Can sometimes cause an inaccuracy in measuring QT interval.

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