Pharmacology
Cardiovascular
Question 17 of 180
A tachyarrhythmia is defined as broad-complex if the QRS duration is:
Answer:
If the patient with a tachyarrhythmia is stable, the QRS duration should be considered.- If the QRS duration is 0.12 seconds or greater, it is a broad-complex tachycardia.
- If the QRS complex is less than 0.12 seconds, it is a narrow-complex tachycardia.
Management of Tachyarrhythmias
Pharmacology / Cardiovascular
Last Updated: 4th August 2021
The approach to the management of tachycardias should follow the Resuscitation Council guidelines.
If the patient has adverse features:
Adverse features:
- Shock (hypotension, pallor, sweating, cold extremities, confusion, impaired consciousness)
- Syncope (transient loss of consciousness)
- Heart failure (pulmonary oedema, raised JVP, peripheral oedema, hepatomegaly)
- Myocardial ischaemia (ischaemic chest pain, ischaemic changes on ECG)
If any adverse features are present, emergency cardioversion with a synchronised DC shock is indicated. If cardioversion fails to terminate the arrhythmia and adverse features persist, amiodarone 300 mg IV over 10 – 20 mins should be given and further cardioversion attempted. The loading dose of amiodarone can be followed by an infusion of 900 mg over 24 h, given via a large vein.
If the patient has no adverse features:
If the patient is stable, the QRS duration should be considered.
- If the QRS duration is 0.12 seconds or greater, it is a broad-complex tachycardia.
- If the QRS complex is less than 0.12 seconds, it is a narrow-complex tachycardia.
Broad-complex tachycardia
Broad-complex tachycardias are mostly ventricular in origin but may be a supraventricular rhythm with aberrant conduction.
- A regular broad-complex tachycardia is likely to be ventricular tachycardia or a regular supraventricular rhythm with bundle branch block.
- A ventricular tachycardia (or broad-complex tachycardia of uncertain origin) should be treated with amiodarone 300 mg IV over 10 - 60 min, followed by an infusion of 900 mg over the next 24 hours.
- If previously confirmed as SVT with bundle branch block, the patient should be treated as for narrow-complex tachycardia.
- A stable patient with an irregular broad-complex tachycardia is most likely to be in AF with bundle branch block, although AF with ventricular pre-excitation or polymorphic VT (torsades de pointes) is a possibility.
- Expert help should be sought for the assessment and treatment of irregular broad-complex tachycardia.
- Torsade de pointes VT should be treated by stopping all drugs known to prolong the QT interval, correcting electrolyte abnormalities, and giving magnesium sulfate 2 g IV over 10 minutes. Expert help should be sought as other treatment options including overdrive pacing may be required to prevent relapse once the arrhythmia has been corrected.
Narrow-complex tachycardia
The narrow-complex tachycardias are supraventricular in origin.
- A regular narrow-complex tachycardia may represent paroxysmal SVT or atrial flutter with 2:1 conduction, it may be difficult to differentiate between the two.
- The first step in treatment of regular narrow-complex tachycardias is to attempt vagal manoeuvres (carotid sinus massage or Valsalva manoeuvre).
- If the tachyarrhythmia persists, adenosine 6 mg IV should be given as a rapid bolus using a large cannula and a large vein. The patient should be warned that they will feel unwell and may experience chest discomfort for a few seconds following the injection. An ECG (preferably multi-lead) should be recorded during the injection.
- If the ventricular rate slows transiently and then speeds up again, this may indicate atrial activity such as atrial flutter or other atrial tachycardia, and this should be treated accordingly.
- If there is no response (i.e. no transient slowing or termination of the tachyarrhythmia) to adenosine 6 mg IV, a 12 mg IV bolus should be given and if there is no response, one further 18 mg IV bolus given (max 36 mg). Lack of response to adenosine will occur if the bolus is given too slowly or into a peripheral vein.
- If adenosine is contraindicated, or fails to terminate a regular narrow-complex tachycardia, the administration of verapamil 2.5 - 5 mg IV over 2 mins should be considered.
- Irregular narrow-complex tachycardia is most likely to be AF with fast ventricular response or, less commonly, atrial flutter with variable AV conduction.
- Immediate treatment options include rate control with drug therapy, rhythm control using drugs to achieve chemical cardioversion, rhythm control by synchronised cardioversion and treatment to prevent complications (e.g. anticoagulation). Expert help should be sought in determining the most appropriate treatment for the individual patient.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
