Some Physiology And Pathophysiology

Cardiac output (CO) depends on the rate of contraction of the heart (HR) and the volume of blood that is ejected with each beat, the stroke volume (SV); it is expressed by the relationship:

The three factors that regulate the stroke volume are preload, afterload and contractility:

• Preload is the load on the heart created by the volume of blood injected into the left ventricle by the left atrium (at the end of ventricular diastole) and that it must eject with each contraction. It


(includes rates inappropriately slow for haemodynamic state)

If appropriate, give oxygen and establish ¡.v.access

Adverse signs?

Systolic BP < 90 mmHg Heart rate < 40 beats nnin 1 Ventricular arrhythmias requiring suppression Heart failure

Atropine 500 jig i.v.

Satisfactory response?

Risk of asystole?

Recent asystole Mobitz II AV block Complete heart block with broad QRS Ventricular pause > 3s

No | Observe

Interim measures: Atropine 500 |tg i.v. repeat to maximum 3 mg Transcutaneous (external) pacing or

Epinephrine (adrenaline) i.v. 2-10 |ig min-'

Seek expert help Arrange transvenous pacing

Fig. 24.2 Protocol for the treatment of pericardiac arrest arrhythmias (arrhythmias) in hospitals.With permission, UK Resuscitation Council.The latest versions can be found on

can also be viewed as the amount of stretch to which the left ventricle is subject. As the preload rises so also do the degree of stretch and the length of cardiac muscle fibres. Preload is thus a

Broad complex tachycardia

(treat as sustained ventricular tachycardia)*

If not already done, give oxygen and establish i.v. access

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