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Review
. 2005 Oct;90(10):1086-90.
doi: 10.1136/adc.2005.076984.

Understanding cardiac arrhythmias

S Chakrabarti  1 , A G Stuart
Affiliations
Review

Understanding cardiac arrhythmias

S Chakrabarti et al. Arch Dis Child. 2005 Oct.

Abstract

This review highlights the applied science intrinsic to the interpretation of the electrocardiogram and cardiac arrhythmias in children.

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Figures

Figure 1
Figure 1
Summary of ionic currents involved in the production of the cardiac action potential. Phase 0, rapid depolarisation; phase 1, initial repolarisation; phase 2, plateau; phase 3, repolarisation; phase 4, slow spontaneous depolarisation (only in pacemaker cells).
Figure 2
Figure 2
V1, 4th right ICS; V2, 4th left ICS; V3, between V2 and V4; V4, left 5th ICS, midclavicular line; V5, 5th ICS, anterior axillary line; V6, 5th ICS mid-axillary line. Lewis lead: place the negative electrode over the 2nd right ICS and the positive electrode directly below (4th right ICS). ICS, intercostal space.
Figure 3
Figure 3
Analysis of surface ECG. P–R interval: taken from the start of the P wave to the start of the QRS complex. It is the time taken for depolarisation to pass from the SA node via the atria, AV node, and His–Purkinje system to the ventricles. QRS complex: time taken for depolarisation to pass through the His–Purkinje system and the ventricular muscles. Q–T interval: taken from the start of the QRS complex to the end of the T wave. Represents the time taken to depolarise and repolarise the ventricles.
Figure 4
Figure 4
(A) Premature and escape beats. Supraventricular ectopic beat. The third beat (*) is narrow complex, preceded by an abnormal P wave and occurs earlier than a sinus beat. (B) Supraventricular tachycardia. The arrows depict the P waves following each QRS complex in this atrioventricular re-entry tachycardia 150/minute.
Figure 5
Figure 5
(A) In 1st degree block all impulses conduct to the ventricles but the PR interval is prolonged. In 2nd degree block, every P wave does not induce a QRS complex. In 3rd degree block, none of the P waves are conducted to the ventricles. (B) Alternative picture of complete heart block.
Figure 6
Figure 6
(A) Substrate for re-entry circuit. Two pathways (A and B) form an electrical circuit around a surgical scar. Pathway A has a slower conduction time but shorter refractory (recovery) period than pathway B. (B) Initiation of re-entry circuit. A re-entry tachycardia is initiated when a premature stimulus enters one pathway (pathway A) while the other (pathway B) is refractory. After crossing the pathway, it is conducted retrograde into the other pathway that is no longer refractory. The stimulus then re-enters the initial pathway. This creates a continuous reciprocating tachycardia within the circuit.
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References

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