14. Atrial Flutter Flashcards
You are asked to assess a 57-year-old lady for total abdominal hysterectomy.
She has a history of chronic asthma for which she is on long-term oral steroids and regular home nebulised salbutamol.
An ECG has been performed.
Rate: 80–90 bpm
Rhythm: The rhythm is irregular and flutter waves are present. The rhythm is
atrial flutter with a variable block, varying between a 2:1 and a 4:1
block.
Axis: The axis is at zero degrees.
How do you calculate the axis?
Normal cardiac axis is −30 to +90 degrees.
Less than −30 degrees represents left axis deviation.
The simplest way to resolve cardiac axis is to use the net QRS
deflection in leads I and aVF.
Lead I is at 0 degrees and lead aVF is at +90 degrees, i.e. they are
perpendicular to each other; therefore, resolving the vectors in these
two leads will give the axis.
If lead I has a positive deflection and aVF a positive deflection, the axis
has to lie between 0 and +90 degrees.
In this case, lead I is very positive and aVF is isoelectric (i.e. one in
which the R and S waves are of equal size) so the vector lies at 0 degrees.
There is no contribution to the vector from aVF.
Another approach
is to first identify an isoelectric lead.
Theoretically, the axis must lie perpendicular to this lead.
In this example aVF is isoelectric; therefore, the axis lies either at zero
degrees or 180 degrees.
As lead I (counter clockwise to aVF) is positive and III (clockwise to aVF)
is negative, the axis is zero degrees.
Another useful tip – if lead aVR is positive, then the axis is abnormal
because it has to lie between less than −60 ◦ or greater than 120◦.
Why may the patient be in atrial flutter?
The atrial flutter may be due to
her chronic respiratory disease,
her treatment or
due to other pathology.
Why may the patient be in atrial flutter?
Respiratory disease
Chronic respiratory diseases such as
chronic asthma and COPD result in
increased pulmonary vascular resistance and right ventricular strain.
Increased right ventricular pressures lead to right atrial dilation,
which may trigger atrial dysrhythmias.
Furthermore, hypoxia and acidosis may increase the incidence of dysrhythmias.
Why may the patient be in atrial flutter?
Treatment
Salbutamol is a beta-adrenergic agonist.
It has a high degree of B2 specificity.
However, at higher doses significant B1 effects occur.
This produces tachycardia and reduces the threshold for atrial dysrhythmias.
Furthermore, B-agonists and steroids may produce hypokalaemia.
Atrial flutter may also be caused by
other disease processes such as:
Ischaemic heart disease
Hypertension
Thyroid disease
Cardiomyopathies or myocarditis
Rheumatic/valvular heart disease
Carcinoma of the bronchus
Alcohol abuse.
How do B2-agonists like salbutamol work?
B2 adrenergic receptors are G(s) protein coupled receptors.
They are found mainly on smooth muscle cells.
These receptors consist of seven transmembrane domains
and interact with G protein complexes on the intracellular surface.
Binding of an agonist causes a conformational change in
the B2 receptor resulting in the Gs protein complex releasing GDP
and binding GTP, thus activating the complex.
The GTP/alpha complex dissociates from the
beta/gamma subunit and activates adenyl cyclase to produce cAMP.
What happens with the increased cAMP
The increase in cAMP activates protein kinases
causing active calcium compartment shift resulting
in smooth muscle relaxation and bronchial dilatation.
Direct potassium channel activation by G proteins
may also increase smooth muscle relaxation.
The G-alpha subunit has intrinsic GTPase activity resulting in the
hydrolysis of GTP to GDP returning the complex to its inactive state.
B2-agonists also inhibit mast cell de-granulation and may inhibit vagal tone.
How would you manage her atrial flutter?
A history should be taken to assess symptoms of cardiac insufficiency and an
examination performed.
Check electrolytes, thyroid function tests and a chest X-ray.
Refer the patient to a cardiologist for further investigation and
management.
An echocardiogram can be performed to assess cardiac function and
structure.
Rate control does not appear to be an issue here but may be necessary in
some cases.
Suitable agents are beta-blockers
(may not be appropriate in this case), verapamil or digoxin.
How would you manage her atrial flutter?
Rhythm control with electrical or chemical cardioversion may be considered
after an echocardiogram and appropriate anticoagulation (>3 weeks with
INR >2.0).
Anti-thrombotic therapy with warfarin or aspirin may be considered after
stroke risk categorisation in accordance with the NICE guidelines. The
annual risk of stroke in chronic AF is 3%–7%.
Patients with recurrent atrial flutter may be considered for tricuspid isthmus
ablation.
When would you anaesthetise her?
Consult with the surgeon regarding the urgency of the surgery.
Ideally the procedure should be delayed until the management of her atrial flutter and
asthma have been optimised.
