Supraventricular Tachycardia

Life update- finished two weeks of my haematology firm and I’m enjoying it fairly well. The consultant wants us to be around and looks out for attendance but he is also pretty keen to teach us. Yesterday, for example, we did some bedside teaching with him and we got to listen to a metallic heart valve, see a patient with pulmonary fibrosis (wheeze, crackles and clubbing) and a patient on chemo and steroids for lymphoma who had cushingoid features and inguinal lymphadenopathy. All in an hour’s work.

Essentially, we did a bit of ‘sign hunting’, except that whereas, we might go wandering wards looking for good signs, he already had a map and took us on a tour. If you’ve got a good sign in hospital, you are essentially a celebrity and all the medical students and even the F1s want to come and have a listen to your metallic heart valve. So, that patient, who didn’t even speak much English, knew what was up when a group of medical students came to see her.

In other news, exams are fast approaching and I’m starting to freak out a little bit on the inside. And for anyone who hadn’t noticed the recurrent theme, I’m reviewing cardiovascular conditions. Just a heads up.


Supraventricular Tachycardia

Image result for cardiac conduction system diagramDefinition: a disturbance of cardiac rhythm (arrhythmia) characterised by narrow complex tachycardia on ECG, which arises from the atrium or the atrioventricular junction.

Aetiology/ risk factors:

Occurs as a result of re-entry circuits in which there are two separate pathways for impulse conduction. Often seen in young patients with no evidence of structural heart disease.

AVNRT (atrioventricular nodal re-entrant tachycardia)- commonest

=Re-entry circuit at the AV node

AVRT (atrioventricular re-entrant tachycardia)

=due to presence of an accessory pathway that connects the atria and ventricles and is capable of antegrade and/or retrograde conduction.

Wolff-Parkinson White Syndrome is the best known type of AVRT. There is a congenital accessory pathway (Bundle of Kent) which bypasses the atrioventricular node causing ventricular pre-excitation. WPW may also present as SVT due to pre-excited AF or pre-excited atrial flutter.

Image result for wolff parkinson white syndrome bundle of kent

Causes of arrhythmias include:

Cardiac: MI, coronary artery disease, LV aneurysm, mitral valve disease, cardiomyopathy, pericarditis, myocarditis, aberrant conduction pathways.

Non-cardiac: caffeine, smoking, alcohol, pneumonia, drugs (Beta-2-agonists, digoxin, L-dopa, tricyclics, doxorubicin), metabolic imbalances (K+, Ca2+, Mg2+, hypoxia, hypercapnia, metabolic acidosis, thyroid disease), and phaeochromocytoma.

Epidemiology:

More common in young adults, with a female predominance.

Symptoms:

-rapid regular palpitations usually with abrupt onset and sudden termination

-dizziness, dyspnoea, central chest pain, syncope

-exertion, coffee, tea or alcohol may aggravate the arrhythmia

Signs:

usually normal cardiac examination

During episode of arrhythmia:

tachycardia

-regular, rapid pulse

-may be sweaty, hypotensive, cool skin

-lung crackles (from pulmonary vascular congestion)

Investigations:

→ECG/ 24 h ECG monitoring

-narrow complex tachycardia- HR > 100bpm, QRS width < 120ms

-p waves are absent or inverted after QRS

Image result for supraventricular tachycardia ecg

 

Wolff-Parkinson-White Syndrome (AVRT)= short PR interval and wide QRS with delta wave (slurred upstroke) when in resting sinus rhythm. ST-T changes.

Image result for wolff-parkinson white  ecg

Electrophysiology

May do an echo to detect any associated cardiac abnormalities

-CXR, U&Es, toxicology screen

Management:

-The aim is to restore and maintain sinus rhythm.

If haemodynamically compromised = DC Cardioversion (shock)

Acutely:

1) vagal manoeuvres: e.g. breath holding, carotid sinus massage, valsalva manoeuvre = transiently increase AV block.

2) IV adenosine (6mg IV bolus, saline flush, if unsuccessful after 1-2min, give 12mg, then 12mg again)

Adenosine-

S/E- transient chest tightness, dyspnoea, headache, flushing

CIs- asthma, 2nd/ 3rd degree heart block, sinoatrial disease (unless pacemaker)

3) IV verapamil, if adenosine fails and not on a beta blocker (5mg over 2 mins, if unsuccessful- 5mg after 5-10mins)

Alternatives: atenolol or sotalol

→If drugs not working – DC cardioversion

Maintenance: beta blockers or verapamil

Wolff-Parkinson-White Syndrome: definitive treatment is with radiofrequency ablation of the bundle of Kent.

Radiofrequency ablation is increasingly used in AVRT and in many patients with symptomatic AVNRT.

Complications:

-patients are prone to atrial and occasionally ventricular fibrillation

-rare: myocardial ischaemia, MI, congestive cardiac failure, syncope, cardiomyopathy, sudden death

Prognosis:

usually well tolerated in the absence of structural heart disease

radiofrequency ablation of an accessory pathway via a cardiac catheter is successful in about 95% of cases

References: Kumar and Clarke’s, Cheese & Onion, Rapid Medicine, Medscape
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