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ECG Interpretation

Avoid Misinterpretation - 5 Tips

Whether you're in medical school or an experienced physician, it is easy to misinterpret the ECG. In this article we present five easy tips in avoiding the most common mistakes. Read more

Time and the ECG - Part 1

In this video we show you how to calculate the heart rate from an ECG in the presence of a regular and irregular heart rhythm.

Cardiac Electrical Activity

Contraction of the atria and ventricles is tightly coordinated by a wave of depolarisation spreading through the muscular walls of these chambers.

ECG Lead Perspectives

The different leads of the ECG examine cardiac electrical activity from different perspectives. In this video we teach you the perspectives of the 12 ECG leads on cardiac depolarosiation and repolarisation.

ECG Generation

The leads of the ECG machine detect the movement of the cardiac depolarisation and repolarisation waves as they spread through the atria and ventricles.

ST Elevation Myocardial Infarction

When an atheromatous plaque ruptures in a coronary vessel and the clot which forms completely obliterates the vascular lumen, the entire thickness of the myocardial wall supplied by that vessel becomes ischaemic and is at risk of infarction.

Axis Deviation - Recognition

In this video we show you how to identify right and left axis deviation on the ECG.

Bundle Branch Block

Isolated dysfunction or damage of either of the main branches of the bundle of His is commonly observed in clinical practice.

Atrial Fibrillation and Flutter

Atrial fibrillation is the commonest cardiac arrhythmia encountered in clinical practice. In this condition, chaotic electrical impulses, generated from multiple sites within the atria and pulmonary veins, result in irregular depolarisation of the ventricles with a resulting irregularly irregular heartbeat.

AV Nodal Re-entrant Tachycardia

The combination of an unfortunately timed atrial ectopic and the existence of two strands of conducting tissue with opposite electrical properties in the junctional region of the heart can establish a rapidly discharging, self sustaining, re-entrant loop of depolarising current.


Tachycardia is defined as a heart rate of 100 beats or more per minute. When faced with a tachycardia on the ECG, identification of the anatomical location and nature of the focus of depolarising current generating the arrhythmia has a critical bearing on treatment.

Arterial Blood Gas - Featured Videos

pH Disturbances - Introduction

In this video we introduce some fundamental concepts and terms used in arterial blood gas (ABG) analysis.

Mass Action

In this video we show you how a knowledge of the chemical principle of ‘mass action’ helps us to predict and identify pH abnormalities on the arterial blood gas (ABG).


In this video we show you how physiological compensatory mechanisms influence the pattern of changes produced on the arterial blood gas (ABG) in different pathological situations.

Predicting Patterns

In this video we show you how we can use the principle of ‘mass action’ combined with knowledge of the effects of physiological compensation to predict the four basic patterns of pH disturbance on the arterial blood gas (ABG).

The Anion Gap

The anion gap is a fundamental concept in the analysis of metabolic acidosis.

Bedside Rules

Clinical studies have established expected levels of compensation in pH disturbances. Identification of deviation from these ‘bedside rules’ can help us to identify mixed acid-base disturbances on the arterial blood gas (ABG).

Derived Values

The derived values (standard base excess and standard bicarbonate) represent an attempt to separate metabolic from respiratory effects on the arterial pH.

Mixed pH Disturbances

Identification of mixed acid-base disturbances on the arterial blood gas (ABG) can be useful diagnostically. There are certain ‘clues’ on the ABG readout which should raise the possibility of a mixed disturbance.

The Delta Ratio

Continuing with the theme of mixed pH disturbances, the delta ratio helps us to pick up mixed metabolic acidosis due to a combination of ‘base-loss’ and fixed-acid addition.

Oxygen Measurements

In this video we explain the relationship between the three measures of arterial oxygenation reported on the arterial blood gas (pO2, the SaO2 and the CaO2).

Control of Respiration

In this video we review the basic physiological mechanisms controlling respiration and which in turn determine arterial oxygen and carbon dioxide levels as measured on the arterial blood gas (ABG)

The A-a gradient

In this video we discuss the mechanisms underlying the alveolar-arterial oxygen gradient (A-a gradient) and the importance of this concept in analysis of the arterial blood gas (ABG).


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The electrocardiogram is one of the most important diagnostic tools in acute medicine. In this course, we use straightforward language and graphics to explain in simple terms how the normal ECG readout is generated and presented. We then go on to explain how the ECG is used to diagnose diseases of the heart. As indicated in the links above, the course is divided into 5 sections; the normal ECG, Axis and Chambers, MI and ischemia, Arrhythmias and Miscellaneous. These sections should be studied in that order. Each of the 5 sections is further divided into a small number of videos. The videos in each section combine to form a single lecture and again should be viewed in the order indicated. At the end of each section there are a series of simple tests which are designed to consolidate the knowledge you will have acquired. These tests should be completed before moving on to the next section.

We have tried to emphasise aspects of ECG interpretation which we wish had been explained to us at the start of our careers! Some of the sections are currently in progress and will be available on-line in the coming year.


Arterial Blood Gas

The arterial blood gas (ABG) is a fundamental test in hospital practice. Abnormalities of arterial pH are seen in many different pathological situations. The ability to interpret pH abnormalities on the ABG can aid in the diagnosis of these conditions. In addition, identification of abnormalities of arterial oxygenation and their correction is a life-saving basic medical intervention.

In this course, we teach you the basics skills involved in interpreting abnormalities of pH and oxygenation on the ABG. This is a challenging area and the challenge is compounded by the fact that different countries use different units on the ABG readout. This course is available in the units in use in the United States (US units) and the SI units (SI units) used in much of the rest of the world. In some countries a mixture of different units are used! For this reason, on some of the ABG readouts two values are quoted for some biochemical measurements. Find out which units are in use in your country and log-on to the appropriate section.