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.