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Flashcards in ECG Deck (24):

waht is a wave?

a deflection, positive or negative, away from the isoelectric line


what is a complex?

several waves


a segment?

a straight line between waves/complexes



a segment and a wave


Timing on ecg?

Vertical lines

1 small box = 0.04sec

1 large box = 0.2 sec


voltage on ecg?

horizontal lines

0.10mV=1small box



Normal duration of




PR:  120-200 ms (3-5ss)

QRS  <=120ms (3ss)

QT   <= 0.5 RRinterval

cQT=QT/ (square root from RR interval)


Heart rate calculation

No. Of beats in 300 large squares = beats in 1 min

300/(number of large squares between two R waves) 

  OR (number of QRS) x 6   in the rhythm strip

1500 small squares = 1 minute

1500/(number of small squares between two R waves)


a broad T wave means what?

A broader T wave ↔ ↑ heterogeneity of repolarization among cardiac muscle cells →it takes longer (temporal dispersion of refractoriness). This is the substrate for re-entry.


QT interval:

what does it measure and what does its prolognation mean?

A long QT interval (a measure of the duration of repolarization) may identify the patient at risk for ventricular arrhythmias and sudden death.

The QT prolongation of hypocalcemia has somewhat less risk. This is the only cause of QT prolongation where the duration of the T wave is not prolonged—a normal T wave just occurs later.


Upward or downward QRS complexes and concordant T waves in which leads?

In the young:

Upward & concordant:   I, II, III, aVF, V3-V6 

DOwnward & concordant:  aVR, V1, V2


In older adults, T waves are upward in V2 and sometimes V1 despite the fact that QRS are downward.




Physiological Q waves represent what?

Normal parameters?

Physiological Q waves represent the upwards depolarisation of the septum (in II, II, aVF)

In V6, V5 leads, the Q wave represents Lefto to Right septal depolarisation.

Normally, q wave is <0.04s (<1ss wide), no deeper than 25% of subsequent R wave.


Left Bundle Branch distribution and actions

Left bundle branch (LBB) branches into:

1. Left anterior fascicle (LAF).LAF depolarises ant & lat walls of LV.

2. Left posterior fascicle (LPF).
LPF depolarises the post & inf surfaces of LV simultaneously.

3. Septal branch



Normal cardiac axis

Normal cardiac axis – leads I,II, II have positive QRS complexes.

Normal cardiac axis -  -30˚ to 90˚, if the axis lies beyond aVL (-30˚) → left axis deviation (LAD).

If beyond aVF (90˚) →right axis deviation (RAD).


Left Axis Deviation due to & appearance:

due to LAF bkock

 Left anterior descending artery pathology (ischemia, infarction),




 As the axis moves towords the left, III begins to delelop s wave, even further, lead II will also develop an s wave. Lead I retains a stron r wave At the limit of normality, the axis lies at a VL = lead II is isoelectic (r wave= s wave).
In the LAD:  negative leads II & III, strongly positive --  lead I


Right axis deviation due to

due to LPF block usualy, diffuse ischemia/infarction, cardiomyopathy. Local ischemia rarely ahs a significant effect because of extensive anastomosis of blood supply.

Loss of a large part of LV myocardium due to MI (left lateral infarction), shifts the axis to the right and vice versa.


QRS complexes in LAD & RAD

In both LAD and RAD – QRS complexes are wider (but still within normal range) due to a slight delay of depolarisation in the affected area.


DIagnostics of LVH

Sokolow-Lyon: S wave in V1 + R wave in V5 or V6 (whichever higher) ≥3.5mV  

OR  R wave in V5 or V6 > 2.3mV


Cornell: R in aVL + S in V3 > ♂2.8mV or ♀2.0mV


RVH diagnostics

R wave > 7ss  in lead V1 


R:S ratio >1 in V1 suggests RVH.


In what lead is P wave normally negative?



Normal P wave measurments

Normal Pwave is

<2.5ss (0.11s)


<2.5mm amplitude.


RA enlargement

RA enlarges downward and to the right → amplitude  of P wave↑ (>2.5mm (2.5 ss) in II, III, AVF)  in inferior leads, but the width is still normal.


LA enlargement

LA enlargement →prolongation of P wave (> 2.5ss). Also, increased asynchrony results in notched P wave (two peaks = P mitrale). If the peaks are >0.05s (1ss) apart, it is indicative of LA enlargement. May produce a negative deflection after a P wave in V1 (>1ss in width and depth)