Discussion:
Spontaneous coronary artery dissection is an important cause of ACS that
is increasingly recognized with use of cardiac imaging modalities.
Reported risk factors include connective tissue disorders, fibromuscular
dysplasia, as well as chronic inflammatory
disorders1,3,5. SCAD has also been associated with
extreme emotional or physical triggers much like Takotsubo’s
cardiomyopathy1,3. It has a predilection for young,
otherwise healthy middle-age women without any traditional
cardiovascular risk factors. Although it is quite rare amongst the
general population, in a select population of young women who present
with ACS, SCAD accounted for up to 24% of cases3.
There are documented cases of SCAD occurring in different age groups
ranging from the second to eighth decade of life. With increasing
awareness of this once elusive entity, it is estimated that SCAD may
cause from 0.1%-4% of ACS cases and LAD appears to be the most
commonly affected vessel1,3,5. These patients are at
high risk for recurrence of MACE. Major cardiac events within 5-7 years
are reported at 15-37% and at 10 years was estimated to be
approximately 50%. The majority of these events were related to
recurrent SCAD1,6,7.
Despite its similarity to atherosclerotic ACS in clinical presentation
as well as propensity for coronary ischemia, PCI should not be routinely
performed because of the increased risk of complications and limited
success1,2,4. In addition, the majority of SCAD
lesions spontaneously resolve without any
intervention1,4,5. Therefore, conservative therapy is
recommended over PCI for stable patients without ongoing ischemia. For
patients with high-risk lesions or hemodynamic instability, PCI and CABG
have been performed, but trials comparing outcomes of conservative
versus have revascularization outcomes are
lacking1,4,5.
Outcomes of SCAD can range from complete resolution to infarction,
cardiomyopathy, ventricular arrhythmias and sudden cardiac death. Saw et
al. published a cohort study in 2019 of 750 patients who presented with
SCAD with 8.1% presenting with ventricular arrhythmias. The rate of
MACE at 30 days was quite high at 8.8% although mortality during this
time period was less than 1%7. This study had short
follow up and did not define patients at highest risk of lethal
arrhythmias and sudden cardiac death. Longer follow up and risk
stratification is needed to clearly identify the at-risk population.
Literature review shows, 3-11% of SCAD patients present with
ventricular arrhythmias or sudden cardiac death1,2. In
this case report, patient initially received wearable external
defibrillator and subsequently underwent ICD placement, due to her
recurrent sudden cardiac arrest(SCA) caused by SCAD. While individual
cases of ICD implantation for secondary prophylaxis for SCA in SCAD have
been reported, there is no consensus on timing or criteria for ICD
placement in these patients. The risk of SCA was higher in patient with
tobacco abuse, ST-segment elevation at presentation, pregnancy status
and recurrent SCAD8. A retrospective study by Lane et
al., found that multivessel SCAD had more than twice the incidence of
SCD (34% vs 16%) compared to single vessel SCAD but did not show any
benefit for external or internal defibrillator placement in patients
with SCAD and SCD9. There are no existing guidelines
to identify SCAD patients at highest risk of ventricular arrhythmias and
sudden cardiac death. Prospective or large retrospective studies looking
at SCD risk in SCAD as well as role of ICD in SCAD patients who present
with SCD, are lacking. The risks and benefits of this invasive procedure
should be further evaluated with long term follow up to establish
practice standards. Our patient likely represents a sub group with high
risk for both SCAD as well as SCD and may have been a good candidate for
ICD placement following her first cardiac arrest. This patient was
fortunate enough to suffer her lethal arrhythmias inside the hospital,
as out of hospital cardiac arrest have lower likelihood of survival to
discharge compared to in hospital cardiac arrest (10-12% vs
25%)10. Studies are needed to identify SCAD patients
who have higher risk for recurrence of SCAD as well as SCD.