Chapters Archive – Page 15 of 22 – The Cardiovascular

Figure 1. Maximum heart rate equation.

Chronotropic incompetence (inability to increase heart rate)

Chronotropic incompetence: inability to adequately increase heart rate Chronotropic incompetence is an independent predictor of overall and cardiovascular mortality. The condition is very common among…

Figure 1. Premature ventricular contraction (complex/beat). Typical appearance. Note the paper speed 50 mm/s (1 large box equals 100 ms).

Premature ventricular contractions (premature ventricular complex, premature ventricular beats)

Premature ventricular contractions (premature ventricular complex, premature ventricular beats): ECG and clinical implications Premature ventricular complexes are also referred to as premature ventricular beats, premature ventricular contractions or just ventricular beats/contractions/complexes.…

Figure 4. Premature atrial beat with incomplete compensatory pause.

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

Premature atrial contraction (premature atrial beat / complex) A premature atrial contraction is produced by an impulse discharged from an ectopic focus located anywhere in the atria. In…

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

Indications, contraindications and subject preparations for exercise stress testing (exercise ECG) In this article, we will discuss indications, contraindications, and subject preparations. We will also discuss the relevance…

Figure 10. ECG reaction in chest leads during recovery.

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

Introduction to exercise stress test (treadmill test, exercise stress ECG) Exercise stress testing has been used routinely for over 60 years to evaluate cardiopulmonary function and to…

The normal electrocardiogram (ECG) waves. ECG interpretation.

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

ECG Interpretation: definitions, criteria, and characteristics of the normal ECG waves, intervals, durations and rhythm This is arguably one of the most important chapters throughout…

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

The ECG leads Before discussing the ECG leads and various lead systems, we need to clarify the difference between ECG leads and ECG electrodes. An electrode…

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

Cardiac electrophysiology: Membrane potential, action potential, automaticity and electrical vectors Video lecture The following video lecture summarises this chapter. The action potential includes a depolarization (activation)…

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

Principles of cardiac electrophysiology and electrocardiography (ECG) To ensure effective cardiac pumping function, the atria and the ventricles must be activated rapidly and sequentially. Rapid activation…

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)

Sinoatrial arrest & sinoatrial pause (sinus pause/arrest): ECG characteristics & clinical implications A sinoatrial arrest occurs when the sinoatrial node does not discharge an impulse…