Chapters Archive – Page 16 of 23 – The Cardiovascular

Figure 4. Premature atrial beat with incomplete compensatory pause.

Premature atrial contraction (premature atrial beat / complex): ECG and clinical implications

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Figure 1. Lead placement for exercise ECG. Note that the precordial (chest) leads are placed normally. The limb leads are relocated to the torso, or proximally on the limbs. The lead placement depicted here is referred to as Mason-Likar's placement, with limb leads on the torso. This reduces artefacts (muscle disturbances) during exercise stress testing.

Indications, Contraindications, and Preparations for Exercise Stress Testing

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Figure 10. ECG reaction in chest leads during recovery.

Introduction to exercise stress testing (treadmill test, exercise ECG)

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The normal electrocardiogram (ECG) waves. ECG interpretation.

ECG interpretation: Characteristics of the normal ECG (P-wave, QRS complex, ST segment, T-wave)

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Figure 18. The organization of the limb leads. Note that the electrode on the right leg is not included in any lead, but serves as a ground wire. Leads I, II and III are Einthoven's original leads, and they can be presented with Einthoven's triangle (lower panel). Leads aVR, aVL and aVF were constructed by Goldberger; their reference point is the average of two electrodes. Lead aVR can be inverted into lead –aVR which is recommended as it may facilitate interpretation. All modern ECG machines are capable of presenting both aVR and -aVR.

The ECG leads: Electrodes, limb leads, chest (precordial) leads and the 12-Lead ECG

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Figure 7. The action potential in the sinoatrial node and in contractile myocardial cells. Phase 4 of the action potential in the sinoatrial node is called 'pacemaker potential', because it is responsible for the spontaneous repetitive depolarization.

Cardiac electrophysiology: Action potential, automaticity and vectors

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Figure 1. The cardiac cycle starts when cells in the sinoatrial node discharges an action potential that spreads as an electrical impulse through the atria and – via the atrioventricular node – to the ventricles. As the impulse spreads through the myocardium, it activates the cells which respond by contracting. The action potential generates electrical currents which gives rise to the classical ECG waveforms presented here. Activation of the atria is reflected as the P-wave and activation of the ventricles results in the QRS complex. The T-wave reflects the recovery (repolarization) of the ventricles. Note that the ECG rarely shows atrial recovery (repolarization) since it coincides with ventricular depolarization (i.e QRS complex), which has much stronger electrical potentials.

Cardiac electrophysiology and ECG interpretation

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Figure 1. Sinoatrial arrest. Also note the ST-segment elevations (which in this case has no relation to the sinoatrial arrest).

Sinoatrial arrest & sinoatrial pause (sinus pause / arrest)

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Figure 1. ECG changes seen in left ventricular hypertrophy (LVH) and right ventricular hypertrophy (RVH). The electrical vector of the left ventricle is enhanced in LVH, which results in large R-waves in left sided leads (V5, V6, aVL and I) and deep S-waves in right sided chest leads (V1, V2). Right ventricular hypertrophy causes large R-waves in right sided chest leads and deeper S-waves in left sided leads.

ECG in left ventricular hypertrophy (LVH): criteria and implications

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Sinoatrial block (SA block): ECG criteria, causes and clinical features

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