POTD: QTc Prolongation

POTD: QT Prolongation

Today’s POTD is thanks to Dr. Haines, who pointed out to me the weird values on the top left of our EKG’s. Namely, the QTcF vs. QTcB. Simply put, they’re just different ways of calculating the QTc.

Briefly about the QT interval.

What is it?

Time from the start of the Q wave to the end of the T wave. Represents time taken for ventricular depolarization and repolarization.

-       QT interval shortens at faster heart rates

-       QT interval lengthens at slower heart rates

-       A quick way to estimate prolonged QT  the QT should be less than half the preceding RR interval

Prolonged values are…

·     > 440ms in men

·     > 460ms in women

·     QTc > 500 is associated with an increased risk of torsades de pointes

·     QTc < 350 is short

Causes of QTc prolongation

-       Medications – the list is EXHAUSTIVE. Common one’s we see.

o   Antipsychotics – Haloperidol, droperidol, chlorpromazine, quetiapine, olanzapine

o   Benadryl

o   Zofran (ondansetron)

o   Amiodarone

o   Antidepressants

o   Antbiotics – the -ofloxacin’s, Bactrim, macrolides (azithromycin)

o   Antifungals

o   Methadone

-       Electrolytes – HypoK, HypoMg, Hypocalcemia

-       Hypothermia

-       Myocardial Ischemia

-       Congenital Prolonged QT Syndrome

Torsades de Pointes (TdP) and QT prolongation

Torsades, a form of polymorphic ventricular tachycardia, is the complication that occurs with QT prolongation. The pathophysiology revolves around the delayed repolarization reflected in the QT prolongation, which can cause early after-depolarizations (can manifest as PVCs). If the PVC occurs concurrently with the T wave, known as “R on T” phenomenon, it can cause degeneration of the rhythm into TdP. Incidentally, this is also why we always use synchronized cardioversion on patients with a pulse rather than defibrillation, as shocking a patient on their T wave can also cause “R on T” phenomenon.

TdP is usually short and self-resolving, so mainstays of treatment involve prevention of recurrent TdP. With active TdP, shock. Otherwise, there are a few therapies for potentially preventing future TdP episodes.

Treatment:

-       As for other ventricular tachyarrhythmias, synchronized cardioversion if unstable and defibrillation if pulseless (many times the defibrillator may not be able to sync anyways, so just shock)

-       Magnesium 1-2g IV over 10-15 min, can be repeated, followed by an infusion

-       Treat underlying cause – correct electrolytes, stop offending drugs, cardiac reperfusion therapy, etc.

-       Lidocaine – for refractory TdP. Only non-QT prolonging agent compared with amiodarone and procainamide.

Prevention of TdP:

-       Overdrive pacing – no great evidence. The idea is to increase the HR of the patient to shorten the QT interval. Transvenous is preferred. Target is typically ~100-110BPM

-       Isoproterenol – also no great evidence, can use prior to pacing to medically increase the HR.

o   5mcg/min (0.1mcg/kg/min in children)  target HR 100 or 30 above natural HR

o   For both overdrive pacing and isoproterenol, may need to titrate HR to whatever will prevent the patient from going into TdP

Now, back to the original clinical question…

The QTc estimates the QT interval at a standard heart rate of 60 BPM. If the HR is 60 on your EKG, you can just use the QT =).

·     Bazett formula: QTC = QT / √ RR

·     Fridericia formula: QTC = QT / RR 1/3

·       Note: The RR interval is given in seconds (RR interval = 60 / heart rate).

The Bazett formula is the most commonly used because of its simplicity. The Bazett formula overcorrects at HR > 100 and under corrects at HR < 60. If the HR is >100 or <60, the Fridericia formula should be used instead. No, I’m not savvy enough with math to explain why.

Some tips when calculating your own QTc

-       Use the lead with the longest, easily measurable QT interval

-       Where the maximum slope of the T wave intersects the isoelectric line determines the end of the QT interval

MDCalc has great calculators for calculating your own QTcs.

Random Questions

1)    Does magnesium decrease the QTc?

A: No. Thought to stabilize the myocardium through an unknown mechanism.

2)    What do I do with my asymptomatic patient’s with QTc > 500?

A: Admit them? Honestly, I have (although they were sent in by their cardiologist for elevated QT). Doesn’t appear to be a clear cut answer… likely hinges on multiple factors like ability to follow-up, comorbidities, number of QT prolonging medications, discussion with PCP, etc.

https://litfl.com/qt-interval-ecg-library/

https://litfl.com/polymorphic-vt-and-torsades-de-pointes-tdp/

https://first10em.com/torsades-de-pointes/

https://emcrit.org/ibcc/tdp/

POTD: EMS Termination of Arrest

POTD: EMS Termination of Arrest (NYC)

Today’s POTD is thanks to Dr. Friedman and influenced by a cardiac arrest case last week. In very short summary, an elderly male with a history of COPD witnessed (?) cardiac arrest on the street and was ultimately brought to the ED with ongoing CPR after 40 minutes of ACLS in the field. Asystole/PEA. They were already intubated on arrival, and ROSC was achieved ~10min after arriving to the ED. 

We were debriefing the case afterwards when the comment came up that EMS didn’t terminate in the field because it was in the street, and if the arrest had happened in the home they would have called for termination. Which prompted the question: When do pre-hospital providers consider termination of resuscitation vs. transport to the hospital?

Termination of Resuscitation shall be considered for cardiac arrests with all of the following criteria:

Patient Characteristics

• Age ≥ 18 years old

• Arrest etiology is non-traumatic or is not due to any of the following:

• Drowning

• Hypothermia

• Suspected pregnancy

• Lightning injury/electrocution

• Suspected overdose

• Hanging/asphyxia

Resuscitation Components:

• Unwitnessed arrest without bystander CPR

• At least 30 minutes of EMS resuscitation time, including at least ALS resuscitative care for 20 minutes

• No return of spontaneous circulation (ROSC) during resuscitation at any time

• No defibrillation is performed during resuscitation at any time

• Rhythm remains in asystole or PEA (rate < 40) throughout resuscitation

• Arrest does not take place in a public area

Important Exceptions to TOR Guidelines

1.     Resuscitation attempts should be immediately terminated upon presentation of a valid DNR (Do Not Resuscitate) order. TOR criteria do not need to be met to halt resuscitation when a patient’s DNR status is identified.

The following DNR orders may be accepted by prehospital providers (other DNR orders cannot be honored in the prehospital setting):

a. New York State Department of Health (DOH) Out-of-Hospital DNR form or DNR bracelet.

b. MOLST (Medical Orders for Life-Sustaining Treatment) form indicating DNR status. c. Physician’s DNR order in the medical chart when the patient is in the medical care facility under the physician’s care.

We all know that out-of-hospital cardiac arrests (OHCA) have very poor outcomes at baseline, whether for neurologically intact survival or even just survival until discharge. These numbers are even worse for PEA/Asystole. UpToDate estimates that, for asystole, 10% of OHCA survive until discharge, with 5% surviving with good neurological function. For PEA, the numbers were ~20% survival and ~10% with good neurological function.

Two important factors that are known to improve outcomes are (1) immediate, well performed compressions (most of the time initiated by a bystander) and (2) early defibrillation for shockable rhythms. These factors appear to be heavily involved in the decision making to terminate arrest in the above EMS protocol.

As Q likes to say (and others, I’m sure, but I live with Q), there’s good medicine in these EMS protocols. Personally, I haven’t read many of them, but I’ll be paying more attention from now on.

Lastly, some guidelines on when EMS will initiate CPR.

CPR shall be initiated on all patients who are not breathing (apneic) and pulseless unless the patient has any of the following conditions:

• Extreme dependent lividity

• Rigor mortis 

• Tissue decomposition

• Obvious mortal injury

• Valid do not resuscitate (DNR) order or medical orders for life-sustaining treatment (MOLST) form or eMOLST (Appendix C: Do Not Resuscitate (DNR) / Medical Orders for Life Sustaining Treatment (MOLST)

• Terminal illness is not a contraindication to CPR

• Cardiac arrests secondary to drowning, hanging, or electrocution shall be treated as non-traumatic cardiac arrests

 Pediatric:

• CPR is required for pediatric patients with severe bradycardia (heart rate < 60 beats/min AND signs of shock or altered mental status) 

• If available, pediatric AED/monitor pads and cables shall be used for all pediatric patients age < 9 years 

• If pediatric AED/monitor pads and cables are not available, the adult AED/monitor pads and cables shall be used

• CPR shall be continued until any of the following conditions are present 

• Return of spontaneous circulation (ROSC) 

• Resuscitative efforts have been transferred to providers of equal or higher level of training 

• Qualified, licensed physician assumes responsibility for the outcome of the patient

Thanks,

David

https://www.uptodate.com/contents/prognosis-and-outcomes-following-sudden-cardiac-arrest-in-adults

https://www.nycremsco.org/wp-content/uploads/2020/02/2020-13-REMAC-Advisory-Termination-of-Resuscitation-Physician-Guidelines-REVISED.pdf

Trauma Tuesday: Electrocution Injuries

 Epidemiology

-       3 primary age groups

o   Toddlers – household sockets, appliances, etc.

o   Adolescents – risk-taking behavior

o   Adults – occupational hazard

-       Lightning strikes – account for 50-300 deaths per year in US (mostly Florida)

-       ~6,500 injuries and 1,000 deaths annually from all electrocution injuries

Classification

-       Low voltage: ≤1000 volts (V)

o   Household outlets in US typically 120 V

-       High Voltage: >1000 V

o   Power lines > 7000 V

-       Alternating current (AC) = electrical source with changing direction of flow  household outlets

o   Induces rhythmic muscle contraction  tetany  prolonged electrocution as individual is locked in place

o   Although generally lower voltages, can be more dangerous than DC as the time of electrocution is much higher

-       Direct Current (DC) = electrical source with unchanging direction of current of flow  lightning strikes, cars, railroad tracks, batteries

o   Usually induces a single, forceful muscle contraction  can throw an individual with significant force  higher risk of severe blunt trauma 

Mechanisms of Injury

-       Induced muscle contraction  rhabdomyolysis

-       Blunt trauma

-       Burns

o   Internal thermal heating – most of damage caused by direct electrocution

o   Flash/Arc burns – electricity passes over skin causing external burns

o   Flame – electricity can ignite clothing

o   Lightning strikes can briefly raise the ambient temperature to temperatures greater than 54,000F

Severity of Injury – is determined by…

-       Type of current – AC vs. DC

-       Duration of contact

-       Voltage

-       Environmental circumstances (rain, etc.)

Clinical Manifestations

-       Cardiac – 15%, mostly benign and occur within few hours of hospital stay

o   Arrhythmias - Most occur shortly after the event, though non-life-threatening arrhythmias can occur a few hours after the event and are usually self-resolving. Generally, …

§  DC = asystole

§  AC = ventricular fibrillation

o   Other EKG findings – QT prolongation, ST elevations, bundle branch blocks, AV blocks, atrial fibrillation

-       Pulmonary

o   Respiratory paralysis – diaphragmatic muscle

o   Blunt trauma – pneumothorax, hemothorax, pulmonary contusions, etc.

-       Neurologic – generally, patient can APPEAR DEAD but is the cause of neurologic electrocution and may be temporary. IE.

o   Coma

o   Fixed, dilated pupils

o   Dysautonomia

o   Paralysis or anesthesia

-       Renal – Rhabdomyolysis

-       Skin – All kinds of burns

-       MSK – from severe muscle contractions

o   Always assume C-spine injury

o   Compartment syndrome

o   Fractures/Dislocations

Management – we’ll divide them into categories of severity. Basically, always do an EKG!!

1)    Mild (<1000V) – examples include brief house outlet shock, stun gun

a.     EKG – other work-up such as troponin and CPK usually unnecessary

b.     If history/physical unremarkable (patient endorses brief contact with house outlet) patient can be discharged without further work-up

c.     If PMH puts patient at higher risk of arrhythmia (cardiac disease, sympathomimetics) can do a brief period of telemetry observation

d.    Can always observe 4-8 hours to be on the safe side

e.     High Risk Features

                                               i.     Chest pain

                                             ii.     Syncope

                                            iii.     Prolonged exposure

                                            iv.     Wet skin

2)    Severe Electrocution (>1000V) – industrial accidents, lightning strikes

a.     Coding – pursue usual ACLS

                                               i.     Keep in mind traumatic causes of arrest (tension pneumothorax, etc.)

                                             ii.     KEY FACT: remember that patients with fixed, dilated pupils, no respiratory effort, and no spontaneous movement may only have TEMPORARY neurologic stunning

                                            iii.     Pursue resuscitation longer than usual as patient with ROSC can still have good outcomes  does not appear to be any definitive guidelines on when to terminate, at physician discretion

b.     Otherwise, broad medical and traumatic work-up and likely admission for telemetry monitoring (basically just send all the labs and images)

                                               i.     Start with primary/secondary trauma survey and further imaging as required

                                             ii.     Don’t forget CPK to assess for rhabdomyolysis

c.     Consider transfer to burn center

TL;DR

-       Treat as you would a trauma/burn patient

-       Most household outlet shocks – history/physical, EKG, and likely quick discharge unless high risk features

-       Industrial shocks – at best admit for telemetry. At worst prolonged ACLS as good outcomes are possible. Don’t forget traumatic causes such as tension pneumothorax

http://brownemblog.com/blog-1/2020/4/14/acute-care-of-the-electrocuted-patient

http://www.emdocs.net/electrical-injury/

http://www.emdocs.net/em3am-electrical-injuries/

http://www.emdocs.net/em-cases-electrical-injuries-the-tip-of-the-iceberg-view-larger-image/

https://www.tamingthesru.com/blog/air-care-series/electrocution