POTD: Shock to the heart (and you're to blame)

Hello folks,

Today’s POTD will be a quick overview of implantable cardioverter-defibrillators (ICDs) and their common complications.

Why do patients have an ICD in place?

Secondary prevention in previous episodes of unstable VT or VF.

Primary prevention if pt has hx of severe heart failure or underlying congenital arrhythmias.

Exact indications listed below:

Hx of MI within last 40 days with LVEF of <30%, NYHA Class II or III heart failure with an LVEF <35%, underlying disorders which place them at high risk of unstable VT or VF such as congenital long QT syndrome, HOCM, Brugada, ARVD

What does an ICD do?

Note that all ICDs are also pacemakers, but the reverse is not true (pacemakers do not have defibrillator/shocking functionalities).

Anti-tachycardia function: If the patient is tachycardic above a pre-set range (usually 150-220) the ICD will compare QRS morphology to a known sinus beat and if determined to be different, will deliver a series of paced beats at a rate slightly faster than the native rate to break the re-entrant cycle.

Defibrillation in response to sensed VT or VF

What can go wrong with ICDs?

In short, problems with ICDs/pacemakers come down to a failure of sensing or a failure of pacing.

Pacing malfunction:

Failure to pace: pacemaker doesn’t deliver a stimulus at all, resulting in return of the underlying rhythm.

Failure to capture: pacemaker delivers a stimulus, but the stimulus does not result in depolarization. EKG will show pacer spikes that are not followed by P waves or QRS complexes. 

Sensing malfunction:

Failure of sensing: pacemaker fails to sense normal cardiac activity so an impulse is delivered inappropriately. EKG will show intermittent pacer spikes.

Oversensing: pacemaker identifies external signals such as from skeletal muscle contraction as “appropriate” and will not send an impulse when one is required.

Other problems:

Pacemaker mediated tachycardia: formation of a re-entrant circuit from retrograde p waves being sensed as native atrial activity, causing inappropriate tachycardia. This tachycardia does not exceed the programmed upper limit of the ICD.

Twiddler syndrome: accidental or intentional manipulation of the pulse generator resulting in dislodgement of pacing leads resulting in sx such as diaphragmatic or brachial plexus pacing. Will manifest as arm twitching or uncontrollable hiccups depending on where lead has migrated.

Miscellaneous pearls

• Because most ICDs have only a lead in the RV, a LBBB pattern is expected on EKG; new RBBB pattern/axis deviation may indicate lead migration/dysfunction.

• If you need to externally cardiovert or defibrillate, place pads at least 8cm away from device in anterior-posterior orientation.

• Placing a magnet over the device will remove the defibrillator function of an ICD, but pacing function will be kept. This will be helpful in the setting of inappropriate shocks. Kept in charge nurse desk on north side usually!

• Every patient should carry a pocket card indicating the manufacturer of their ICD, but it can also be ID’d by CXR and using an app called Pacemaker!

• We’re lucky we have electrophysiology as a consult service here at Maimo that can interrogate a device for us, but each company has on-call representatives that will come interrogate a device 24/7.

  • Medtronic Inc. (1-800-328-2518)

  • St. Jude Medical Inc.(1-800-722-3774)

  • Boston Scientific Inc. (1-800-227-3422)

References

https://www.emdocs.net/ecg-pointers-icds-and-when-they-malfunction/

https://www.emdocs.net/em3am-pacemaker-aicd-complications/

https://www.emdocs.net/pacemaker-and-aicd-management-in-the-emergency-department/

https://rebelem.com/pacemaker-basics/

https://coreem.net/procedures/how-to-use-a-magnet/

https://litfl.com/pacemaker-malfunction-ecg-library/

POTD: All About LVADs

Hey everyone,

Today’s POTD will be all about LVADs, something we encounter rarely, but vitally important to know about. Feel free to skip to the bottom for the TL;DR!

What are LVADs?

Left ventricular assistance devices (LVADs) were developed in 1960s as a bridge to cardiac transplant, but is now also used as destination therapy, meaning it is the patient’s final therapy for heart failure during their lifetime. They are typically powered by two batteries with a power base unit that can be plugged into the wall. Indicated for NYHA class 4 HF, ejection < 25%. Note the Heartmate II is the most common one in use today.

Components

Pump: takes blood from cannula in apex of LV and pumps it directly into aorta.

Driveline: percutaneous cable that exits the abdominal wall and connects pump to external components such as controller and battery.

Controller: external “box” containing computer for device. Monitors pump performance and has controls for settings/alarms/diagnostics. Will show pump speed and output. Listed here are the normal range of values.

• Pump Speed: 2200 – 2800 rpm (HeartWare VAD) and 8000 – 10000 rpm (HeartMate II VAD)

• Power: 4 – 6 Watts

• Flow: 4 – 6 L/min

• Pulsatility Index (PI): 1 – 10

Power supply: connected to batteries or power base station which plugs into wall

FOR EMS PROVIDERS: In an emergency, all efforts should be made to transport patients with LVADs to their respective LVAD center. If a patient is brought to a non-device center, it is crucial that EMS personnel make every effort to bring the patient’s peripheral equipment needed to support them until they can be transferred to an LVAD center.

Common complications

Bleeding: most common reason for ED visit, most commonly in first month after implant. Tx with anticoagulant reversal, transfuse if needed. LVADs can cause acquired von Willebrand Disease, thought to be from the action of rotary or axial flow pump of the LVAD which causes high shear stress that may increase lysis of large vWF multimers.

Infection: from driveline and pocket, cover broadly with vanc/cefepime

Pump thrombosis: tx with heparin/antiplatelets or tPA in life-threatening situations. Pts will be on anticoagulation but pump thrombosis can still be common due to prosthetic material inflammatory reaction with blood and intrinsic endothelial activation in response to a continuous flow.

Arrhythmia: tx like you would in pt without LVAD either chemically or with electricity - place pads in anterior/posterior positioning

Suction event: when LV myocardium partially occludes the LVAD inflow cannula reducing inflow. Caused by low LV preload relative to pump speed. Tx by giving fluids, consider reducing LV speed in conjunction with LVAD team.

Cardiac tamponade: refer to LVAD center, pericardiocentesis discouraged b/c of low yield and potential for harm as the LVAD outflow graft may traverse typical course of needle.

Initial assessment FOCUSES ON CIRCULATION:

CONTACT THE LVAD TEAM: here at Maimo, the number is 35CHF

Note patients with LVADs will have NO PALPABLE PULSE and NO DISCERNIBLE HEART SOUNDS. Instead you will hear a continuous hum to confirm device is operating, though newest Heartmate 3 may have some interruptions to hum.

Measure the BP (must use doppler US and sphygmomanometer with doppler placed over brachial or radial artery).

1.        Cuff inflated until pulse no longer audible and then deflated.

2.        BP reading made when arterial flow audible again, giving single reading as MAP.

Goal MAP 70-80 and no more than 90 as this high afterload may compromise optimal function of LVAD. Should place A-line in hemodynamically unstable/hypotensive patients to more closely monitor BP.

Work-up will be the usual things you do for a cardiac patient: EKG, labs including trop, BNP, CXR. BEDSIDE ECHO AND COAGS/HEMOLYSIS LABS will be key because they can lead you down different diagnostic pathways.

Approach to conscious hypotensive patient with LVAD: check flow and power

Low flow vs high flow?

·      Low flow suggests hypovolemia

·      High flow state

o   Normal power or high power?

·      Normal power – distributive shock

·      High power – obstructive shock from thrombosis vs suction event vs cardiac tamponade

Differing schools of thought on CPR in LVAD:

Some argue you should analyze the LVAD first, others say you should begin CPR immediately if a patient comes in with circulatory collapse like you would any other patient.

If you were to analyze the LVAD first, then LOOK, LISTEN, FEEL:

Look at all connections

Listen for hum

Feel (hot control box usually means thrombosis or other obstruction)

Sometimes there is a hand pump attached to LVAD, but if pt unresponsive with MAP < 50 and etCO2 <20, or LVAD cannot be restarted, it is reasonable to proceed with CPR if you're in a setting without an LVAD team.

TL;DR of what to do when an LVAD patient arrives:

CONTACT THE LVAD TEAM through extension 35CHF here at Maimo.

1. Patients with LVADs may have no palpable pulse and that is normal! You should hear a continuous hum on auscultation to verify that it is working.

2. Look at all connections, listen for hum, analyze settings on the box.

3. Measure the BP with a cuff and doppler and aim for a MAP of 70-80, no more than 90. An A-line should be placed for close hemodynamic monitoring.

4. Do a bedside echo and get the usual labs but include hemolysis labs/coags.

5. In a hypotensive patient with an LVAD, low flow is from hypovolemic shock; high flow will either be distributive (normal power reading) or obstructive shock (high power reading).

6. Shocks are okay for the appropriate arrhythmias.

7. If a patient is in circulatory collapse and the LVAD is not working/can't be restarted/there is no handpump, it is reasonable to proceed with CPR if you're in a setting without an LVAD team, but follow your institutional recs. Note that here at Maimo, it is advised not to start compressions.

References

https://emcrit.org/emcrit/left-ventricular-assist-devices-lvads-2/

https://criticalcarenow.com/when-a-vad-goes-bad/

https://www.uptodate.com/contents/emergency-care-of-adults-with-mechanical-circulatory-support-devices

https://first10em.com/lvads/

https://rebelem.com/left-ventricular-assist-device/

https://www.emdocs.net/lvad-patients-what-you-need-to-know/

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