ECG Quiz 1 (Internal Medicine)

There is a regular rhythm at a rate of 60 bpm. There is a P wave before each QRS complex, with a stable PR interval (0.18 sec). The P wave is positive in leads I, II, aVF, and V4-V6; it has a normal morphology and duration (0.12 sec). Hence this is a normal sinus rhythm. The axis is normal, between 0° and +90° (positive QRS complex in leads I and aVF).

For regular rhythm & when 1 mm =0.04 sec

INSTANTANEOUS HR = 300/ No. of big boxes between two consecutive R waves or
=1500/ No. of small boxes between two consecutive R waves OR
= 60/RR interval (sec)


Further reading : Calculation of heart rate in irregular rhythm.

The correct answer is "Deviated to left side." In an ECG, the axis refers to the overall direction of the electrical activity in the heart. A deviation to the left side indicates that the electrical activity is predominantly directed towards the left ventricle. This can be caused by conditions such as left ventricular hypertrophy or left bundle branch block.

Best way to determine the axis of an ECG is to plot hexaxial diagram.
but for quick determination of axis following points can be used.
1) Normal axis - mean QRS complex is positive in both leads I & III/aVF.
2) LAD - mean QRS complex is positive in lead I & negative in III/aVF.
3) RAD - mean QRS complex is negative in lead I & positive in leads III/aVF.

Trick - Draw lead I and then draw lead III/aVF below it. Compare QRS complex.
Normal - Both are pointing upward.
RAD - lead I pointing downward & lead III/aVF pointing upward ( as if they are meeting each other)
LAD - lead I pointing upward & lead III/aVF pointing downward ( as if they are leaving each other)

so RIGHT WE MEET, LEFT WE APART.

A normal T wave has an asymmetrical shape; that is, its peak is closer to the end of the wave than to the beginning.
In contrast symmetrical tall T waves in certain conditions, such as MI and a high serum potassium level are abnormal.

The QT interval is measured from the beginning of the QRS complex to the end of the T wave. It primarily represents the return of stimulated ventricles to their resting state (ventricular repolarization). The normal values for the QT interval depend
on the heart rate. As the heart rate increases (RR interval shortens), the QT interval normally shortens; as the heart rate decreases (RR interval lengthens), the QT interval lengthens. Therefore,rate corrected QT or QTc is preferred in clinical practice. Normal QTc is 350 t0 440 msec.

The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. The PR interval
represents the time it takes for the stimulus to spread through the atria and pass through the AV junction. (This physiologic delay allows the ventricles to fill fully with blood before ventricular depolarization occurs, to optimize cardiac output.) In adults the normal PR interval is between 0.12 and 0.2 sec (three to five small box sides). Prolongation of the PR interval
above 0.2 sec is called first-degree heart block (delay).

Further reading : Heart blocks and types.

The ECG shows a regular rhythm at a rate of 110 bpm. There is a P wave before each QRS complex, with a stable PR interval
(0.16 sec). The P wave is positive in leads I, II, aVF, and V4 -V6, and it has a normal duration (0.10 sec). Hence this is a sinus tachycardia ( not SVT).

The P waves are abnormal, and they are tall, narrow, and peaked in leads II, aVF, and V1-V2. The P-wave morphology is characteristic of a P pulmonale, a result of right atrial hypertrophy. This may also be termed a right atrial abnormality (RAA.)

The axis is rightward, between +90° and +180° (negative QRS complex in lead I and positive QRS complex in lead aVF).

The major finding is a tall R wave in lead V1 , defined as an R wave taller than 7 mm (seven small boxes) or an R /S > 1. The
tall R wave in lead V1 along with the rightward axis and a P pulmonale (right atrial hyper trophy) are characteristic of right ventricular hypertrophy (RVH).

The criteria for the diagnosis of RVH include:
• R-wave amplitude (in mm) in lead V1 > 7 mm
• R/S ratio in lead V1 > 1
• R/S ratio in lead V6 (or V5)
Supporting criteria for RVH include:
• Right axis deviation (between +90° and +180°), which is diagnosed by a QRS complex that is negative in lead I and positive in lead aVF
• Right atrial hypertrophy (P pulmonale); the P wave is tall (> 0.25 mV), narrow ( • Associated ST-segment depression and T-wave abnormalities in leads V1-V3


The combination of RVH and right atrial hyper t rophy on the ECG and a loud P2 on exam suggests the presence of elevated pulmonary pressures. Pulmonary arterial hypertension is clinically associated with scleroderma and is the most likely diagnosis.

The P wave is broad (> 0.12 sec), notched in leads II and V4 (termed P mitrale), and negative in leads V1 and V2. This is characteristic of left atrial hyper trophy, also termed left atrial abnormality (LAA).

the axis is normal, between 0° and +90° (the QRS complex is positive in leads I and aVF).

The major finding is the marked increase in QRS voltage (R-wave amplitude or S-wave depth) seen in the precordial leads (S-wave depth in lead V2 = 39 mm and R-wave amplitude in lead V5 = 40 mm for a total of 79 mm), which is diagnostic for left vent ricular hypertrophy (LVH ) (ie, S-wave depth in lead V2 + R-wave amplitude in lead V5 ≥ 35 mm).

Associated with LVH are ST-T wave changes or repolarization abnormalities seen in leads V4 -V6 . These ST-T wave changes, often referred to as a “strain pattern,”

The proposed criteria for diagnosing LVH include:

1) S-wave depth (in mm) in lead V1 (SV1) + R-wave amplitude (in mm) in lead V5 or V6 (RV5/RV6) ≥ 35 mm especially in middle aged or older adults. (Sokolow-Lyon criteria). This is normal common finding in athletic and thin adults.

2) R wave of 11-13 mm or more in lead aVL is another sigh of LVH.

3) R-wave amplitude (in mm) in lead aVL + S-wave depth (in mm)
in lead V3 ≥ 28 mm for men or ≥ 20 mm for women
(Cornell criteria)

The voltage criteria are based on the ECG recorded at normal standard,
where 1 mV = 10 mm or 10 small boxes in height.