Emergency cardiac pacing options

Cardiac pacing is a Level 1 topic from Section 2.1.19 in the first edition of the CICM Syllabus for the Second Part Examination. One might make the argument that a lot of this belongs in Section 2.1.18 ("Peri-operative issues in Intensive Care") or 2.1.4 (Cardiology)  as well. 

Past paper questions on this topic are numerous:

• Question 1 from the first paper of 2024
• Question 2 from the first paper of 2016
• Question 29 from the second paper of 2013
• Question 10.1 from the second paper of 2009
• Question 3 from the second paper of 2004

Of the learning objectives listed in "for each of the above expected knowledge will include", a lot is already dealt with elsewhere:

• Indications for temporary cardiac pacing, 
• relevant anatomy, 
• insertion procedure for transvenous wires, as well as an entire chapter on external (transcutaneous) cardiac pacing
• advantages and disadvantages (including different modes),
• interpretation of different pacing misbehaviours
• all the contraindications or complications

Which means this section only needs to cover the expected knowledge for some emergency rescue therapies that vaguely fit into the "technique" and "complications" syllabus elements

So, it's failed to capture, and the patient is unstable.

"After the patient is turned, there is sudden failure to capture", reads Question 1 from the first paper of 2024, calm words that cannot possibly reveal the true feeling of betrayal experienced by the night registrar when they realised what the wardsmen and nurses had done to their shift. The options presented in the question (transcutaneous, transvenous and skin lead pacing) suggest that "fiddle with the box and leads" stage of coping with this grief has already passed, and those simple measures have failed to rescue the situation, but let's list them anyway:

• Exclude device problems
• Exclude (or at least rapidly identify) reversible lead problems
• Attempt to readjust the device by increasing the pacing outout to maximum and  perform several potentially futile manoeuvres that might temporarily improve the situation, eg. rolling the patient back on to the side where they still had capture.

Now that none of that has worked, we need to think of other options.

Tolerate bradycardia

Doing nothing is occasionally (always?) an option. The AHA certainly seem to view asymptomatic bradycardia as a non-issue, noting that "there is no established minimum heart rate or pause duration" that is concerning enough to warrant a PPM. From the perspective of the intensivist, indications related to permanent pacing are probably less relevant, and moreover the patient is often insufficiently conscious to report being "asymptomatic". And are they really asymptomatic, if they are maximally monitored and you know they have a lower MAP or urine output with the slower rate. 

The question one has to ask oneself is, "are they going to feel worse if I have to pace them transcutaneously, or place a jugular sheath for wires?" The answer may be "yes". Apart from doing nothing, which is the opposite of a plan, one may instead choose to correct electrolytes that may be contributing, to rewarm the cold patient, reawaken the profoundly sedated patient, return to them their forgotten thyroxine, and wait.

Resort to chronotropes

Waiting may not be an option, but also pacing may not be a very good option. Fortunately, we have a long experience with chronotropes. "It is as a rule possible to achieve results similar to those of pacemaker therapy in complete heart block", even in MI, wrote Christiansen et al (1973), on the basis of no evidence whatsoever (their study had 32 patients, 12 of whom died). The agents used (atropine and isoprenaline) were basically the same as what one might find in a modern ICU. De Lazzari et al (2023) list a series of present-day options directly off the ERC 2015 algorithm, which is representative of many other such algorithms worldwide:

• Atropine or glycopyrrolate
• Isoprenaline
• Dobutamine
• Adrenaline
• Aminophylline
• Dopamine
• Ephedrine

These options each have their advantages and disadvantages. Most of these agents can be infused peripherally and have no serious adverse effects beyond their cardioirritant properties, which some might view as desirable in the context of bradycardia. In short:

• Advantages include:
  • Minimally invasive
  • Safe (mostly)
  • Well tolerated
• Disadvantages
  • Your exotic drug choice may not be available
  • It may be expensive
  • Each drug has their own undesirable side effects, eg. delirium with atropine
  • It may not have a sustained effect
  • Most importantly, it may not work; to say nothing of it being far from definitive therapy

As one might guess, this is not something that has been studied in any great detail, as far as detailed outcomes data is concerned. De Lazzari et al (2023) looked at a cohort of patients with complete heart block who had the option of isoprenaline dopamine or pacing and found that the isoprenaline group were much more likely to get an effective response without having to resort to pacing (84% vs 34%). This surprised nobody because dopamine is a terrible drug and should not be used for anything.

Transvenous pacing

This is described elsewhere. In brief, the technique is:

• An introducer sheath is inserted
• The pacing catheter is floated like a PA catheter
  • One option is to float while attached to ECG like a moving internal lead (Lead 1), looking for the "current of injury" which looks like ST elevation
  • Other option is to turn the pacing on to some predictably effective settings and to watch for capture
• The wire can be guided into the RV using TTE, TOE, fluoroscopy, or just with a chest Xray at the end

Advantages of a transvenous wire are numerous:

• Relatively safe (as safe as a PA catheter, anyway)
• The venous access is a reasonably common ICU procedure
• The same pacing pulse generator is used for this as for the epicardial pacing, which means staff do not need to be trained to use yet another piece of equipment
• This can be in place for a week, if you need it to be
• It is reasonably well tolerated (i.e. painless once in place)

Disadvantages

• Not everyone has had a chance to do this during their ICU training
• Not everybody's ICU stocks  these devices
• Not all support staff know how to use/maintain/troubleshoot the wire, even if they are familiar with the pacing box
• It may not work. It needs to be in contact with some living endocardium, so if there is (for example) a large RV infarct, then there will be little effect from trying to pace the dead muscle.
• It may tangle with, or be impeded by, all kinds of existing hardware, including pre-exisitng pacing leads or various lines.
• If the patient has severe RV failure and TR, the catheter may not find its way into the right position.

Complications include

• Vascular access disasters
• RA perforation and cardiac tamponade
• Cardiac (eg. valvular) injury
• Like the PA catheter, it can coil or knot.
• Accidental dislodgement - there is, ultimately, nothing affixing the catheter tip to the ventricular wall except prayer, so random changes in catheter position and even patient neck positioning can influence where the tip is. This can lead to terrible situations where, for example, the patient only has cardiac output when their head is turned slightly up and to the left.

Transcutaneous (external) pacing

This is covered in a separate chapter on external pacing, to which the reader is referred for what can only be described as an unfairly biased bashing of this technique. It is really not as bad as that, and a professional-sounding summary would have to look something like this:

• Indications for transcutaneous pacing
  • Bradycardia (heart block or otherwise) that does not respond to medical management
  • Overdrive pacing
  • Pacing in the prehospital or austere environment (i.e. where other options are not available)
• Anatomy/ procedure
  • Broad conductive gel pads are placed ideally antero-posterior
  • or, worst case scenario, apex (V5) and right parasternal (V1)
  • Attach pads to the defibrillator
  • Turn the defibrillator to pacing mode (choose VVI mode if the choice presents itself, as VOO risks R on T phenomena)
  • Increase the rate to the desired rate (80-90)
  • Increase the current to max (140-200 mA) for the unconscious peri-arrest patient; or increase in increments of 5-10 mA for the stable conscious patient
  • Confirm mechanical capture with pulse or arterial line to defeat the confusing electrical phenomena that may mimic electrical capture.
• Advantages
  • Widely available
  • Non-invasive
  • Requires minimal skill to implement
  • An improvement over ineffective medical or conservative therapy
  • Usually only a temporary measure
• Disadvantages
  • Requires skill to troubleshoot
  • Is uncomfortable and requires sedation
  • Can cause burns
  • Often ineffective despite pad position changes
  • Not a long term solution
• Contraindications
  • Existing chest wall burns or wounds/dressings
  • Contraindications to sedation (eg. no airway expertise available)
  • Relatively contraindicated in morbidly obese patients (capture will not be achieved even with maximum output)
• Complications
  • Burns
  • Pain and the consequences of sedation
  • Skin reaction to electrode gel
  • Skin tears due to adhesive pads on fragile skin
  • Obscured radiographic findings while pads are in position

Doukky et al (2019) is probably the best reference among the "proper" literature on this topic.

Unipolar pacing using a skin lead

The availability of this option is contingent on there being another lead already in the patient which can be the first pole. In other words, this is an option in the unique scenario where the patient already had epicardial leads implanted, of which one still works and the other for some reason does not. The technique, in this scenario, would be:

• Insert the pacing stitch under the skin
• Insert both of the remaining epicardial pacing leads into the negative terminal of the pacing box
• Connect the new skin lead to the positive electrode
• Pace as per usual (except probably with a much higher threshold, as the resistance to the flow of current will likely be increased by this).

But what if you are not a surgeon, and not inclined to break into the moonlit operating theatre complex in the middle of the night to look through their impossibly disroganised storeroom for the pacing stitch leads? Perhaps you can improvise. Strictly speaking, any conductor will do, but realistically most medical staff are biased towards sharp objects which are sterile and single-use, which makes a small (say, 23G) needle an ideal candidate. The needle can be introduced under the skin and then clamped into the pacing terminal, as demonstrated in this excellent shot contributed by Dr Amit Vaidya:

• Advantages
  • Widely available and very quick (for the needle technique)
  • Minimally invasive
  • Requires minimal skill to implement
• Disadvantages
  • One of the other leads needs to be functioning
  • It may be uncomfortable and could produce muscle twitching
  • The impedance is increased, i.e. capture threshold is higher
  • Not a long term solution (perhaps 1-2 days is as long as you would be able to persist with this)
  • Easily dislodged
  • Unless one has seen such a thing before, one may be reluctant to try it for the fist time, i.e. experienced operator is required
• Contraindications
  • Existing chest wall burns or wounds/dressings
  • Relatively contraindicated in morbidly obese patients (capture will not be achieved even with maximum output)
• Complications
  • Bleeding
  • Failure of pacing (and delay establishing a better method)
  • Infection at the site
  • Pain from inadvertently pacing the pectoral muscles or the diaphragm

Oesophageal pacing

Oesophageal what now? The reader who might quirk a disbelieving brow would be surprised at how well this is known, and how many enthusiastic devotees it has among the critical care community. Yes, it is listed by reputable resources and has a place in the ladder of escalation. Verbeet et al (2003), for example, list some of the unique advantages of this technique, as well as some of the options for its use:

• Technique
  • Pill electrode or special catheter
  • Placed orally or nasally
  • Usually a bipolar electrode (but 4-pole catheters are also available)
  • A lead (Lead 1 ) is measured through the device as it is inserted to find the optimal atrial pacing depth (where the P wave has a maximal amplitude)
  • The optimal atrial pacing site is usually at a depth of around 40 cm from the nares
• Advantages
  • "feasible because of the proximity between the oesophagus and the posterior aspect of the atria"
  • Easy to pace: 5 and 15 mA threshold is usually observed (i.e. similar with epicardial wires)
  • AAI pacing is possible, whereas without dedicated atrial epicardial wires all other temporary pacing is usually VVI
  • Can be inserted quickly, even when CPR is in progress
• Disadvantages
  • Easily dislodged
  • Unpleasant - "a burning chest sensation that most patients tolerate", to say noting of the nasally inserted tube
  • Some commercial systems only do "burst" pacing to overdrive flutter or to do something diagnostic
  • Brachial plexus stimulation and phrenic nerve pacing are reported as side effects
  • If the catheter is too deep, one inadvertently paces the ventricles
• Contraindications
  • All the same contraindications as NG tube
  • Agitated patient with a high risk of dislodgement
  • No other major contraindications, but one might say that the availability of some other more conventional method is more 
• Complications
  • Bleeding, or damage to all the things one usually encounters in the course of traversing the nasopharynx on the way down to the stomach
  • Failure of pacing (and the inevitable sarcasm from the people who watched you do this and kept telling you it wouldn't work)
  • Pain 

Transoesophageal pacing also has a diagnostic purpose: it is uniquely suited to assess certain cardiac structures and processes:

• Sinus node activity
• AV conduction (eg. short PR)
• Pre-excitation
• Discriminating between VT and SVT

It is otherwise a weird thing to do and most people would agree that other methods are both easier and more acceptable.

Transthoracic pacing

Following some kind of pattern of least to most intrusive, one eventually arrives at the kind of techniques that are so cavalier that one might never mention them in polite society. Transthoracic pacing is certainly that. It is remarkable that it keeps coming up in serious reviews of cardiac pacing, considering that is not something anyone has done since probably the 1980s. Even then it was a step of last resort for asystolic arrest.

• Technique
  • Where this is available, there is usually a kit
  • The kit typically comes with an introducer and a pacing wire.
  • the Elecath kit, described by White (1983),  featured "a curved bipolar pacing stylet and a 6-inch, 18-gauge placement cannula"
  • The cannula needle is inserted at the left subxiphoid angle, at 30 degrees to the bed, and directed towards the left shoulder.
  • The intention was to puncture the RV, and in fact "the electrode was presumed to be in the ventricle when a free flow of at least 20 cc of blood was aspirated through the cannula"
  • The pacing electrode was then introduced directly into the ventricle
• Advantages
  • "ease, rapidity, and certainty of placement" was reported to be the main advantage
• Disadvantages
  • "The technique is extremely hazardous, and should be reserved for life-threatening emergencies", warned a young Judith Tintinalli in 1981. 
  • Also, it often did not work
• Contraindications
  • The technique was reserved for patients in refractory cardiac arrest due to bradycardia or asystole, who also seemed to have high grade AV block during periods of ROSC
• Complications
  • Cardiac tamponade was a complication in a large proportion of cases

Percussion pacing

This is one of those therapies that is effective so infrequently that it becomes a case report each time it has been used successfully. Betzer & Allon (2017), Eich et al (2007), Giordano et al (2018), all describe this technique as a "forgotten alternative" to other methods. The technique is very simple; it involves  "using one’s fist to repeatedly strike a patient’s left sternal border in a rhythmic manner". How hard do you hit them? It is difficult to convey something like that in writing. "Serial blows with the ulnar side of the clenched fist from a height of approximately 20- 30cm above the chest to the lower left sternal edge" is the usual description, and papers that report this technique almost always seem to have an image of a physician's fist raised threateningly over a patient's chest. Though it might sound terrible, it is in fact still better than CPR; Dowdle (1996)  reports that "these gentle blows were well tolerated by the patient who continued to mmain conscious and reasonably comfortable throughout" wfor about fifteen minutes. Apparently some have gone for as long as 90 minutes. An advantage of this technique, apart from the instant availability of the equipment, is that unlike CPR, it stimulates the myocardium to contract, and so the stroke volume could be near normal.