THE EMS LOUNGE

Walked into my patient’s room to discover her lying in bed (still restrained mind you), butt naked. Trying not to stifle a laugh, I ask my very confused, delirious patient what on earth is going on: Nurse BCS: Ms. L, what on earth is going on here? Why are you naked? Ms. L ( with a befuddled look on her face, then looking at me like I’m the crazy person): … I’m not naked.

Nurse BCS: 

leave their relatives with dementia or any kind of chronic or acute confusion in A&E alone. We need to know what is normal for them; some people are confused as their ‘normal’, for others it is something entirely new. If we have no idea, we’ll have to assume it’s new, and your relative may even end up with inappropriate investigaitons or treatments because we had to play it safe. Not to mention that being in A&E is scary for them; please be there for your relative, don’t leave them to deal with being sick in a strange place all alone. It’s not fair to the patient or their clinicians.

leave their relatives who cannot speak English in A&E alone.  Again, if they can’t understand, then it’s a scary situation for them. And we also find it hard to communicate with them or take a history. We can get a hold of translational facilities, but it takes valuable time that might affect their care. 

Send in care home residents like the above with a care worker who does NOT know anything about how that resident has been doing the past few days. It’s not very helpful. We NEED to ask questions about whether someone’s been going to the toilet, eating, coughing, in pain, etc. and any carer coming with them to hospital should know this kind of basic information.

There is quite a lot to be said about the medications we use for patients with arrhythmias. It’s easy to get lost as to what drugs do what and how, but thankfully there was a kind enough person by the name of Vaughan Williams, who actually broke them down into separate classes. Each class effects separate parts of the cardiac cycle, ultimately changing the electrical current of the heart.

Cardiac Action Potential

Before looking at the medications, we have to understand the cardiac cycle and how it actually works.

Source: x

The above chart presents the four phases of an action potential in a ventricular myocardial cell and how the electrolytes are used to cause the depolarization and repolarization of myocardial cells.

Phase 0  begins with a slight influx of sodium until it passes the potential threshold. Once past the threshold, more sodium channels will open and flood the cell, causing it the depolarize.

Phase 1 is an efflux of potassium from the cell, causing the cell to reach 0mV.

Phase 2 happens at this point. This is when calcium influx happens, prolonging the repolarization period. This period also goes by the name of an absolute refractory period for the cell, since it cannot depolarize during this time.

Phase 3 Calcium channels close again and potassium continues to efflux from the myocardial cell until the internal cell voltage returns to -90mV. Majority of potassium channels then close and the heart enters phase 4, which potassium is allowed to continue to leak into from the cell.

This process happens anywhere from 60 to 100 times per MINUTE!

Vaughan Williams Classifications

The major purpose of the medications in this class effect they way the cardiac action potential works in the cells of the heart. The drugs usually help to slow down specific phase to the heart and allow the heart to fix itself a bit.

Class I - Sodium Channel Blockers

These medications are designed to disrupt phase 0, causing a prolongation of it. There are 3 subcategories (a,b,c) that are broken down into moderate, weak, and strong.

This article won’t go into great depths, but the major goal of the class is to prolong the QRS complex and prolong or shorten QTi.

Medications include:

Lidocaine

Verapamil

Procainamide

Propafenone

Class II - Beta Blockers (-olol or -alol)

Quite commonly used out of hospital for patients with hypertension, beta blockers are actually a common antidysrhythmic. The basic pharmacology is: by blocking the beta-1 receptor sites, it prevents stimulation of the cardiac muscle to beat faster. The increase of sympathetic tone will decrease the rate the heart will beat.

Medications include:

Propranolol

Metoprolol

Carvedilol

Class III - Potassium Channel Blockers

Similar to the Class Ia medications, potassium channel blockers are used to prolong APD, which can cause a prolongation of ERP. This class of medication is commonly known to treat different ventricular dysrhythmias (Vtach or Vfib). The most common medication for this class is Amiodarone and deserves a post of its own.

It’s most common use is during CPR, when the patient is in pulses Vtach or Vfib rhythm and is then followed by a drip with ROSC is achieved. An important note to make about Amiodarone is it can take 16 weeks to leave the system.

Medications include:

Amiodarone

Sotalol 

Ibutilide

Class IV - Calcium Channel Blockers

Commonly uses for Afib with RVR and PSVT, a calcium channel blocker will prolong phase 2 of the action potion in the cell. The goal is to slow the conduction through the atrioventricular (AV) node, slowing the ventricular tachycardia that is occurring. By prolonging the ERP in the AV node, the heart is able to regulate the rate better.

Calcium channel blockers are commonly prescribed by physicians to assist in the care of such arrhythmias. One side effect of these drugs is it may drop the patient’s BP, so ensure you have an SBP >100 or a MAP >65, prior to administering the medication

Class V - Others

This is the mix bag class. These drugs do not truly fit in any category but are still highly important to mention anyways. Two of these medications are Adenosine and Digoxin.

Adenosine prevents the re-entry of a signal in a sinus rhythm, preventing SVT. A warning though is for patients that have WPW syndrome may cause an increase in heart rate instead, so make sure you’re reading the rhythm correctly.

Digoxin effects vagal tone and is seen less as an emergency drug and more as a maintenance drug for chronic heart issues. A major issue with this drug is it holds a very narrow therapeutic index. Toxicity is quite possible if given too much.

Summary

Each class works in its own way on the action potential in the cardiac conduction system. How they affect the heart greatly determines when and how the medication should be used in different medical scenarios. The point of this article is to help a bit with the pharmacodynamics involved with the medications and to hint at the situations a person in the medical field would use them?

Remember to check out my facebook page. Feel free to send suggestions for possible article ideas, it might pop up some time. Always remember that medicine is an art, just as much as a science.