Rate and axis - 4315 [Compatibility Mode]

Rate and axis - 4315 [Compatibility Mode] - ECG Basics –...

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Unformatted text preview: ECG Basics – Rate and Axis Determination of Rate There There are several ways to determine heart rate and can be classified into the following: 1. 1. Quick, Global Methods 6 second method (need a 6 second rhythm strip) second Ruler Ruler method Triplicate Triplicate method (300-150-100-76–65–50) (300-150-100-76–65– 2. R to R method (precise) Practice with Rate 1. 6 second method 300 150 100 300 150 100 2. Triplicate method Goldberger & Goldberger, 94 1 Using the R to R Method to Calculate Heart Rate There are generally 4 different ways to use the R-R Rmethod to determine HR and all are based on the a paper speed of 25 mm/sec and that we want HR to be expressed in bts • min-1 1. 60 / (# sm. boxes • 0.04 sec) (ex) (# 2. 300 / (# of large boxes) (ex) 3. 1,500 / (# of sm. Boxes) (ex) 4. Rate conversion table 300 / # large boxes 1500 / # small boxes 300 / 4 = 75 bts • min-1 1500 / 10 = 150 bts • min-1 Goldberger & Goldberger, 94 60 / (# sm. boxes • 0.04 sec) 60 / (26 • 0.04 sec) = 57.7 = 58 bts • min-1 Goldberger & Goldberger, 94 2 Axis: Sum of the all electrical forces in the myocardium representing the main cardiac vector. main -90 ° 0° 180 ° ~60° +90 ° Vectors and Axis Determination in the Heart Refers Refers to orientation of the sum of all cardiac vectors in the heart Axis Axis –angle of orientation of the main cardiac vector (Limb Leads – frontal plane) Normal Normal : between –10 degrees to +100 degrees Transition Transition zone – refers to R wave progression in precordial leads (horizontal plane) Concept of Vectors and Axis Huszar, 1994, pg37 3 Hypertrophy (hyp) and Enlargement (enl) Hypertrophy Hypertrophy – increase in muscle mass Usually Usually caused by pressure overload Hypertension Hypertension Enlargement dilatation of cardiac chamber Enlargement – dilatation of cardiac chamber Usually Usually caused by volume overload Valvular Valvular insufficiency Most Most of the time we should not use the ECG to distinguish between the two as they may coexist. However, we may use the same ECG criteria to evaluate hypertrophy and enlargement ECG manifestations of hyp or enl Increase Increase in duration of wave May May take longer to depolarize Increase in amplitude Increase in amplitude May May be greater amount of muscle mass to depolarize Shift Shift in the main cardiac vector or axis of the axis of heart Determination of Axis using the ECG There There are several methods to determine axis. We We will use Lead 1 and Lead AVF Lead Lead See overheads See overheads 4 Hexaxial Quadrant System -90 ° Lead I = Lead AVF = Lead I = Lead AVF = 0° 180 ° Lead I = Lead AVF = Lead I = Lead AVF = +90 ° Precise Precise determination of Axis Generally knowing that axis is normal or abnormal may be sufficient, but we may also need to know the exact angle angle of orientation of the axis 1. 2. 3. Determine if axis is normal or abnormal and in which quadrant the angle of orientation will lie. li Look for the limb lead in which the QRS complex is most biphasic in orientation (equally positive and negative from the baseline). The angle will lie perpendicular (90°) from the angle of the (90° biphasic wave. (EXAMPLE) Axis as it relates to pathological states Left Left ventricular hypertrophy Left Left axis deviation Right ventricular hypertrophy Right ventricular hypertrophy Right Right axis deviation 5 ...
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