Understanding Digoxin

 Most of us have heard of, or encountered a patient taking Digoxin at some point in our carreers. But, do we understand what it is and how it affects our patient?
 

 Digoxin (Lanoxin), is a Cardiac Glycoside, derived from the foxglove plant, Digitalis. This medication is often seen in the pre-hospital setting, used for the treatment of:

 

  •  Heart Failure (HF) with reduced Systolic Function

 

  • Atrial Fibrillation (AF) and Atrial Flutter (A-flutter) associated with Rapid Ventricular Response (RVR)

 

  • Cardiomyopathies

 

  • Often combined with Calcium and Beta Channel Blockers, Angiotensine Receptor Blockers (ARBs) and diuretics

 

 Why does the rate matter?

 Well, as ventricular rates increase, ventricular filling times (Preload) during rest (Diastole) decrease. This can lead to reduced Stroke Volume (SV) and Cardiac Output (CO). This decrease in CO can lead to further complications like Reflex Tachycardia (further increasing oxygen demand), Chest Pain, Dyspnea and other related symptoms.

 

Remember the basics?

 

 

CO = SV x HR
 

 

Digoxin pharmacology:

 

  •  Inhibition of Sodium (Na+) Potassium (K+) ATPase Pump  leads to increased Na+ and decreased K+ intracellular

 

  •  This increased intracellular Na+ influx then triggers Calcium (Ca+) channels to open and increase Ca+ influx, while at the same time, some Na+ is removed from the cell

 

  •  Since Ca+ is responsible for increased contractility (Positive Inotropic effect), there is an increased myocardial contractility leading to greater CO without increased Myocardial Oxygen Consumption (MVO2)

 

  •  Slight Parasympathetic stimulation leads to reduced AV Nodal conduction which leads to increased Preload, improving Stroke Volume (SV) and CO, however, it can lead to decreased Pulse Rate since there is a decrease of impulses entering the ventricles

 

***Digoxin has a prolonged Half-life, between 35-40 hours average, which in the patient with decreased kidney function or metabolism, increases the Bioavailability (the amount of medication available in the bloodstream for use) which will lead to cardiac toxicity.***

***Digoxin also has a narrow Therapeutic Index (the gap between good treatment and toxic effect) which leads to the cardiac toxicity.***

 

 

Digoxin and ECG changes:
 

 

 

  •  ST segment “scooping”, similar to an ice cream scoop shape, with a rounded negative ST segment. This is also know as "Reverse Check" or "Reverse Tick"

 

  • Atrial arrhythmias like AF with slow RVR

 

  • Junctional, Accelerated Junctional and Junctional Tachycardias

 

  •  Decreased AV Nodal conduction can lead to AV blocks and Ventricular Escape Beats since the above conduction is delayed

 

  •  Bi-directional Ventricular Tachycardia (BVT) which is seen as alternating ventricular beats,  e.g.  LBBB pattern beat followed by a RBBB pattern beat which continue alternating.

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Comments
know it all parapup
83 Year Old Male: Shortness of Breath
@ Kyle I would question your authority to call out people for not having a license or being a know it all parapup when your tx basically entails "call medical control." I think we can both agree that his cardiac output is not great at all. I assume your reluctance to give him any other…
2014-10-30 20:26:11
Kyle
83 Year Old Male: Shortness of Breath
Well st elevation in avr and v1 associated with anterior and lateral depression would call for possible posterior wall MI. 15 lead would be in order. Also check all the leads for appropriate placing. If v7, v8, and v9 show the elevation i would treat as a STEMI per my protocol. Asprin only until medical…
2014-10-30 18:14:05
Tim
The most awesome STEMI test on the internet!
Thanks for the app. It made me think about all that one may see in the field. The only problem was I never got a score or saw the results of how I did other than saying I had completed the test. Anyway a great way to get the old brain working.
2014-10-30 13:14:27
Brian
83 Year Old Male: Shortness of Breath
I mostly agree with dustin. I believe this is may be an isolated posterior MI. The R wave in V2 points to it being a posterior MI. otherwise it is a 1st degree av block with a LAHB. I am somewhat concerned with the concordant t segment depression noted and in fact if you were…
2014-10-30 04:22:44
Karl Brennan
Understanding Amiodarone
Great article , however in VF caused by hyperkalemia it should be avoided along with lidocaine , Since it shuts down the K channels, the eiteiology of the arrest hyper K, K channels are needed to exchange K in the cell. Calcium , Bicarbonate, dextrose and insulin should be used to decrease K levels along…
2014-10-30 03:04:45
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