What do you mean, "refractory"
The VT electrical storm
This topic has never become a CICM SAQ but is sufficiently awesome to merit a whole long discussion. This "storm" concept has no fixed scientific definition. The name borrows some aggressive meteorological associations, evoking images of brooding clouds alight with electrical discharge. Generally, authors in their frustration refer to "incessant ventricular arrhythmia" or "recalcitrant ventricular tachycardia". The UpToDate chapter on this topic lists about five different classifications, as follows:
- VT which fails to terminate after appropriate AICD therapy
- VT which recurs more than twice in the same 24 hr period
- VT in which one episode follows another within 5 minutes
- VT ectopic beats outnumber sinus beats within one 24 hr period
- VT which is ongoing and which is slower than the AICD programmed termination rate
The management recommendations are quoted from ARC guidelines wherever possible; obviously the ARC are not going to recommend weird therapies, and those were mined from Google searches and the personal experience of ICU staff and cardiologists. Of the latter, the author is personally grateful to the contributions of Ben Seymour who sent in some excellent suggestions for fourth and fifth-line therapies.
First line therapies
Before you call something "super-refractory" and reach for the exotic drugs, you've got to have made the effort of trying a few of the well-accepted therapies first.
Amiodarone is widely quoted as the as the first-line agent. Generally speaking, people tend to give a 300mg dose, followed by an infusion of 900mg. ARC Guideline 11.9 ("Managing acute dysrhythmias") recommends this dose, with no reference. The doses of amiodarone in Australia are generally in multiples of 150mg because this is the ampoule size and people for some reason tend to feel bad about wasting this precious iodinated molecule. Beyond that, there does not seem to be any sense to it. In actual fact, the loading dose of amiodarone is 5mg/kg, which comes to 350mg in a 70kg person, or 500mg in a 100kg person.
The next agent to try is lignocaine. The dose is 3-4mg/kg for the first half hour, followed by 2-3mg/kg for the next hour, and then ongoing infusion of 1mg/kg. ARC Guideline 11.9 ("Managing acute dysrhythmias") recommends this drugs with exactly the same level of recommendation - Class B, Level IV. Just as amiodarone, the use of lignocaine is described by the ARC as "reasonable" - not "a splendid idea' or even merely "we recommend". At least in life-threatening episodes of VT, lignocaine has consistently come off as second best to amiodarone and is therefore treated as the second choice of first-line agent, even though the recommendation from the ARC is of the same strength.
VT storm tends to have self-exacerbating adrenergic effects. The extra and intra-cardiac preconditions for the storm tend to be exacerbated by the hyperadrenergic effects of being repetitively shocked by your AICD (or by the ICU team). The patient is physically and psychologically traumatised by living for many days with the anticipation of the next shock, which really hurts and which could occur without any warning and at any time.
Beta-blockade may have some positive effect, and UpToDate lists these among the first-line agents, but the ARC does not. There is a 2014 joint AHRA/ACCA/EAPCI position statement which supports the use of IV metoprolol in VT storm. These agents help modify the sympathetic overactivity associated with being cardioverted repeatedly. The same statement recommends using sedating agents such as benzodiazepines.
Which beta-blocker should you use? Surprisingly, there's some relevance to your choice. Though beta blockade is apparently the goal, in fact it appears propanolol (with its sodium channel blocking properties) has some advantage over metoprolol (as a surrogate for all classical agents). Chatsidou et al (2018) demonstrated that AICD-implanted outpatients treated with propanolol presented with VT storm much less frequently than matched metoprololled controls.
This drug is an important one to mention, even though it is not available locally. CICM trainees from Australia and New Zealand will not find it on the shelves of their hospitals, but its use elsewhere is widespread. The popularity of this Class 1 agent has increased since it compared so favourably with amiodarone in the PROCAMIO study (Ortiz et al, 2017). The study question was which of procainamide or amiodarone would win, in a 20-minute race with sinus rhythm being the finish line. The patients receiving procainamide were almost twice as likely to be cardioverted (67% vs 38%), including those in whom the heart was structurally abnormal. Though there was a 30% incidence of hypotension among the procainamide group, because the positive haemodynamic effects of defeating the arrhythmia counteracted this side effect the drop-out discontinuation rate was only 11%.
Second-line: electrical therapy
ARC Guideline 11.9 ("Managing acute dysrhythmias") recommends the use of cardioversion with the aim of converting a VT which has been going on for too long in spite of first-line drugs, or which has become haemodynamically unstable. How long is too long? "Several hours", apparently. Specific time frames cannot be recommended because there is no uniformity as to how long a person may safely remain in VT. Presumably, after a few hours of VT they will become unstable purely because of poor organ perfusion and myocardial ischaemia, and then some reason to shock them will develop.
The ARC do not make any specific recommendation regarding the selection of energy for this cardioversion. Historically, 100J is the starting pitch; one may wish to go higher if there is no sustained effect.
Generally speaking, the "VT storm" is a consequence of events and conditions which are frequently either extracardiac (and therefore not amenable to cardiac electrical therapy) or which are cardiac and crudely structural (and therefore not fixed by electrical therapy). In short, unless the underlying problem is fixed, one may not have any sustained effect from a single direct current cardioversion (Alsharif et al, 2014)
Transvenous overdrive pacing
The next option is transvenous pacing. Overdrive pacing can also be tried externally but it is usually very unpleasant and is less likely to be effective than transvenous pacing. The idea is to start a coordinated rhythm which is faster than the VT, and then to gradually slow the rate ("decremental" pacing). In fact, this is usually what he AICD will do.
A drug-resistant electrical storm seems to be a good indication for the use of temporary overdrive pacing (Kurisu et al, 2005). It works in situations when drugs do not. Case reports indicate that one may continue in this fashion for 24-48 hours: plenty of time to coordinate some sort of definitive therapy. One may drive at 110-120 bpm for such a period with little risk of myocardial damage, in most circumstances.
Phenytoin is a Class Ib agent, and the dose is exactly the same as for anticonvulsant purposes (15mg/kg). This is incredibly old-school - see Harris et al (1950) and Leonard et al (1958). Occasionally, a review article about it is written, and interest is temporarily rekindled. The most recent such review is by Wang et al from the MJA (2013). The toxicity of this drug has made it obsolete when nicer agents were introduced. Among its many unpleasant effects is the tendency to increase pacemaker threshold, resulting in the loss of capture.
Sodium lactate is a well-known chemical constituent of Hartmann's solution among other things, but its antiarrhythmic effects are less well known. The effect is thought to be the result of alkalinisation, which changes the function of the voltage-gated sodium channel and decreases its binding affinity for proarrhythmic ligands (Scanu et al, 1991). Again, this was all the rage in the 1950s (see Bellet et al, 1957). It used to be available as a molar solution (i.e. 1000mmol/L).
Sodium bicarbonate is a well-known solution to the QRS widening problem in acute tricyclic overdose; however its use in ventricular tachycardia is less well known. Case reports exist of VT being terminated by sodium bicarbonate boluses (eg. Donovan et al, 1999), although in all these cases the arrhythmia is due to an overdose or adverse drug effect of some sort. Again, the effect probably has something to do with reduced affinity of the toxic drug for its receptor. This strategy is less likely to work in some sort of non-toxicological ischaemic VT.
Invasive sympatholytic measures
Beta-blockade may have some positive effect, but there are too many spare receptors, and one may need to resort to more aggressive measures.
Stellate ganglion block
Stellate ganglion block has achieved successful VT storm termination in case reports, many of which end up published in anaesthetic pain medicine journals (Patel et al, 2011). Descriptions in the literature (Nademanee et al, 2000) suggests that these procedures are best performed by peripheral nerve block experts because they involve stabbing the patient in the neck with a 10cm 21g needle. The left-sided procedure is performed by the anterior paratracheal approach.
"A 21-gauge needle was passed anteriorly between the trachea and the carotid artery to within several millimeters anterior to the lateral process of the spine. Ten to 20 mL of 1% xylocaine (without epinephrine) was injected until Horner’s syndrome or partial Horner’s syndrome developed".
The authors report better rates of VT storm control with this treatment, as compared to the conventional ACLS amiodarone/lignocaine cocktail. However, there was a disturbing dispairty in group mortality: of the ACLS-treated group, only 5% survived the first week, whereas of the stellate ganglion block group 67% were still alive.
If stellate ganglion block is insufficiently aggressive for you, thoracic epidural has been used as a means of decreasing the sympathetic flow to the irritable myocardium (Bourke et al, 2010; Tung et al, 2015). Neuraxial blockade of descending sympathetic myocardial innervation is a valid therapy because the analgesia of the epidural might be as effective as the actual sympathetic ablation. If one cannot feel one's chest wall, being cardioverted loses much of its fear factor.
Neuraxial sympathetic ablation tends to act as a prelude to total surgical myocardial sympatholysis. Thoracic epidural creates a sufficient decrease in VT burden to make the subsequent surgery safe from the anaesthetic standpoint. This rather dramatic permanent option is most appropriate for those patients in whom the VT originates from some sort of incurably structural heart disease, such as an unresectable LV aneurysm, or from some nightmarish incurable congenital disorder. Wilde et al (2008) reported on surgical left cardiac sympathetic denervation in three young adults with catecholaminergic polymorphic VT, all of whom were symptom-free following the procedure. It must be mentioned that this approach - though "minimally invasive"- is not without risk:
"Left cardiac sympathetic denervation is performed in 35 to 40 minutes, after an incision is made at the base of the neck; an extrapleural approach is used, without opening the chest. The lower part of the stellate ganglion is ablated together with the second and third thoracic ganglia; the fourth ganglion is cauterized. Preserving the upper half of the stellate ganglion prevents the occurrence of Horner's syndrome"
Radiofrequency ablation and endocardial resection
If drugs and overdrive pacing have not been successful and the stellate ganglion block seems too outré, catheter ablation may be the answer. The 2014 joint AHRA/ACCA/EAPCI position statement recommends the use of radiofrequency catheter ablation to destroy the origins of the VT. Reported acute success rates are up to 72%, with only 6% experiencing recurrence of VT storms. Unfortunately, there is a procedural mortality rate of around 3% - all from intractable arrythmia. After the procedure, the mortality rate in the long term is still around 18%, albeit from heart failure rather than VT. To put this into context, the mortality rate from RFA is still better than the mortality from doing nothing about the electrical storm.
Endocardial resection and "arrythmorrhaphy" are procedures which are the ventricular equivalent of the star-pattern atrial endoablation for AF. These are maximally invasive, least survived, and should probably be reserved for the small population of patients who have VT storms, are well enough to survive cardiac surgery, and who for whatever reason cannot have RFA.
Let's say your patient is either too unstable or too ancient and decrepit to undergo anything invasive, and drug therapy has not been effective. An attractively noninvasive alternative exists. One could simply blast the mapped arrhythmogenic region with 25 Gray of photons in the 6-18 MeV energy range, as a single fraction. Cuculich et al (2017) reported on a series of five patients in whom the frequency of VT was massively reduced, apparently at no cost of systolic function or (permanent) lung damage. Unfortunately, the full extent of radiation damage takes months or years to evolve. One of the patients from the study died of a stroke, suspected to have been embolic (originating from the irradiated myocardium). Moreover, the inflammatory changes from such a humongous dose of single-fraction radiation are far from benign. VT could be exacerbated in the first few weeks of treatment. None of the reported patients had any serious cardiac side-effects but one can imagine that the soft inflamed myocardium would be susceptible to ventricular aneurysm formation, free wall rupture, and subject to an increased rate of atheromatous coronary artery disease.