As I expected , my earlier algorithm “An Idiot’s approach to tachy-arrhythmias” has elicited mixed reactions .Some EPs calling it a dud while few physicians termed it awesome . Here is a follow up .
Heart rate of a tachycardia is the most neglected parameter by physicians . They are often seen spending hours together for decoding arrhythmia , splitting the brains for P wave location , VA conduction, Fusion beats etc .Finally they end up either administering Amiodarone a broad spectrum anti arrhythmic agent or DC shock.
Here is an unusual algorithm for arriving at a diagnosis in all tachy-arrhythmias based only on heart rate and the width of he qrs complex.
(Click over the table for high resolution image )
General principles in diagnosis of tachycardia
Narrow qrs tachycardias.
90 % rule : If regular It is sinus tachy if irregular it is A-FIB . Take some efforts to r/o sinus tachycardia . (In children and young adult it can be extremely difficult at times )* Please note : Sinus tachycardia can show some irregularity due to sinus arrhythmia and frequent APDs and JPDS . Further at fast rates P may fuse with T it should not be confused with A-fib .
Wide qrs tachycardia
Common things are common , if you sight a large animal with a huge trunk in a Kenyan safari , it is most likely to be an elephant and not a Dinosaur ! Please diagnose VT when you encounter wide qrs tachycardia by default especially when the BP drops !
Management issues
It would be foolish to split our heads for decoding an arrhythmia when a patient is unstable .Any hemo-dyanmic unstable tachycardia needs DC shock . (Synchronized will be better unless it is dire emergency )There are very few arrhythmia where DC shock is contraindicated ( MAT/Dig toxicity/Underlying sinus node dysfunction )
Only if the patient is hemo-dynamically very much stable the physicians have enough time to confuse themselves and the real ordeal begins .Please remember the 5 arrhythmias constitute 98 % of all known tachy-arrhytmia . So where ever you practice , whether in remote Nigerian village or sophisticated Cleveland university hospital , when you are confronted with a tachycardia the diagnosis should be one among the following five !)
- Sinus tachycardia .
- AF/A-fib
- Atrial tachycardia with or without blocks
- ventricular tachycardia /VF
- AVNR/AVRT with or without aberrancy
All other tachy-arrhythmiaa are largely academic !
Regarding drugs
Knowing the mechanism of arrhythmia genesis is less important at bed side . They are triggered , sustained, and maintained by either functional or structural component .Ionic basis operates in every arrhythmia , but it is the anatomical substrate that maintains it .This happens in only diseased heart.The only point worth remembering regarding mechanism of arrhythmia genesis is , automatic and focal tachycardias will not respond to DC shock . All other can be termed some form of re-entry . Micro reentry for all practical purposes behave like triggered activity. Ischemic and electrolytic VTs are primarily ionic based and often polymorphic.Structural VT are commonly mono-morphic. Any VT just prior to degeneration to VF become polymorphic
Every patient with cardiac arrhythmia should be checked for hypoxia,acidois , electrolyte defect or exposure to any pro arrhythmic drugs. (The commonest cause of tachycardia in any IMCU , is inotropic induced (dopamine /doubtamine ) tachycardia .
We have 5 pharmacological options
- Blocking adrenergic receptors(IV Esmolol, Metoprolol)
- Blocking calcium channel (Dilitazem,Verapamil)
- Blocking potassium channel (Amiodarone ,Sotolol Adenosine to a cetian extent )
- Blocking sodium channel . ( Procainamide , Lignocaine (Wonder drug almost forgotten now ! ) Flecanide Mexilitene etc)
- Digoxin ,Adenosine magnesium are special anti-arrhythmic agent which has very useful role in certain specific situations (Magnesium -Torsades/Polymorphic VT / Adenosine in LVOT/RVOT VT etc)
General principle is ventricular arrhythmias are blocked successfully by sodium or potassium blockade Atrial and functional tachycardia are blocked by calcium or adrenegic blockade .Of course, there would be some degree of overlap when the arrhythmia origin hovers around the junction on either side of the AV ring . This is basis of verapamil sensitive VT .Clusters of calcium channels are scattered in the junctional region
Refractory tachycardia
- Consider ablation in AVNRT/AVRT
- ICD +Drugs in VT
- Ablate and Pace(Some A-fibs)
- Ablate and ICD (Some incessant VTs)
- Surgery in minority
In AVNRT/AVRT 90 % success can be achieved in most EP centers .VT ablation is still a complex process with success rate around 60 % ICDs are indicated in all recurrent VTs except incessant forms .(Where the battery will deplete within a month !) Surgical cure (Maze etc ) is possible in selected few while undergoing mitral valve surgery.Contrary to the modern scientific mood , I can ay with conviction most A-fibs can be managed medically except a fraction will require pulmonary vein ablation / isolation .
Final message
Mastering the field of of cardiac arrhythmias , though appear a daunting task , it does not require immense sense to understand real world problems are only a few and can be tackled in a simplistic manner !
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Dr.S.Venkatesan MD 