Out-of-hospital cardiac arrest

Sundar Chidambaram*

Consultant Interventional Cardiologist and Endo Vascular Specialist, Kauvery Hospital, Chennai, India

Background

Out-of-hospital cardiac arrest (OHCA) has attracted increasing attention over the past years because outcomes have improved impressively lately. The changes for neurological intact outcomes have been poor but several areas have achieved improving survival rates after adjusting their cardiac arrest care. The pre-hospital management is certainly key and decides whether a cardiac arrest patient can be brought back into a spontaneous circulation. However, the whole chain of resuscitation including in-hospital care has improved also. This article describes aetiologies of OHCA, risk and potential protective factors, and recent advances in the pre-hospital and in-hospital management of these patients.

Case Presentation

Case 1

A 37-year-old male, smoker, obese, had syncope and cardiac arrest at his workplace. He was taken immediately to a nearby hospital. He was resuscitated with CPR and inotropes and shifted to our hospital. ECG showed ventricular tachycardia. He was given DC shock several times. He was in cardiogenic shock.

He was shifted to cathlab. His angiogram showed acute left main coronary artery occlusion with thrombus. The coronary intervention was performed. Thrombosuction was done. Left main to LAD was stented with 4 mm × 28 mm Xience Xpedition (Abbott Inc USA). IABP was inserted and inotropes were continued. His acidosis was treated.

He made a gradual recovery and his inotropes were weaned off and IABP removed.

Case 2

A 43-year old male, a non-smoker, tested positive for COVID-19. While being transported to the hospital he had breathlessness and cardiac arrest. He was resuscitated immediately in the ambulance. In the hospital, ECG showed acute inferior wall myocardial infarction. He was in cardiogenic shock. He was treated with inotropes and shifted to cathlab. With all the protocols for COVID-19 followed, he was taken up for a coronary angiogram. Angiogram revealed right coronary artery occlusion with huge thrombus. Thrombosuction was done, followed by angioplasty with 3 mm × 23 mm xience xpedition (Abbott Inc USA) and 4 mm × 15 mm xience xpedition (Abbott Inc USA). He made a gradual recovery.

Case 3

A 70-year-old male, non-smoker, diabetic, was taken to a nearby hospital for complaints of giddiness and light headedness. He was diagnosed with acute IWMI and complete heart block. While being shifted to our hospital he had a cardiac arrest. He was resuscitated at the outside hospital and shifted here. His ECG revealed Ventricular tachycardia. DC shock was given and immediately shifted to cathlab. His coronary angiogram revealed right coronary artery occluded with thrombus. Temporary pacemaker and IABP were inserted. RCA angioplasty was done with 3mmx23mm xience xpedition (Abbott Inc USA). His neurological recovery was gradual and made a full recovery on 8th day.

Discussion

The high mortality associated with Sudden Cardiac Arrest (SCA) emphasises the need for early identification of patients at risk. However, very little is known about the risk factors. Since coronary artery disease is the most important cause of SCA, cardiovascular risk factors also increase the risk of OHCA, especially so in the case of diabetes and smoking, but less so for obesity.

However, our understanding of the relationship between acute myocardial ischemia and its most fatal immediate consequence, cardiac arrhythmia, remains very limited. We know that ischemia alters repolarisation and it prolongs the QT interval. The extent of QT prolongation during an acute coronary artery occlusion depends on the degree of collateralisation. Intriguingly, there is increasing evidence that the collateral circulation has a protective role during early ischemia. A study in 170 patients with acute anterior infarction showed lower incidence for malignant arrhythmias (defined as VF, VT, or high degree atrioventricular (AV) block) and lower mortality in patients with angiographically well-developed collaterals. Furthermore, a well-developed collateral circulation has been associated with reduced risk for cardiac and all-cause mortality in patients with stable coronary artery disease in general.

Role of heart catheterization and Per Cutaneous Intervention (PCI) after SCA

Importantly, current guidelines recommend immediate referral of patients after OHCA to a cardiac center with onsite cardiac catheterisation facilities in patients after SCA. The decision by the pre-hospital emergency medical service (EMS) provider, where to admit the patient after an OHCA is crucial. Several non-randomised observational studies have demonstrated survival benefit from early angiography post-OHCA compared to no coronary angiography or percutaneous coronary intervention (PCI). However, other studies have also highlighted an increased complication risk if early angiography is performed in these patients. In our view, although the role of immediate coronary angiography is controversial, substantial information on coronary circulation can guide in-hospital management beyond coronary intervention. For example, in patients with cardiogenic shock, an intra-aortic balloon pump (IABP) or other support devices (e.g. Impella 2.5) can be inserted at this occasion to augment cardiac output.

Moreover, approximately 80% of OHCA presenting with VF or VT are cardiac in origin and these patients may benefit from an early PCI. Studies are currently underway to determine whether patients who fail to achieve the return of spontaneous circulation (ROSC) at the scene and who are suspected to have obstructive CAD may benefit from PCI whilst receiving continuous CPR. Importantly, PCI plays a major role in the improved survival rates. In a study of 714 OHCA patients referred to a tertiary centre in Paris, 435 (61%) had no obvious extracardiac cause. This subgroup underwent early coronary angiography and 70% of those had at least one significant coronary lesion.

To facilitate decision-making, an ECG should be recorded as soon as possible after ROSC to assess for ST-elevation or (new) LBBB. However, the ECG has limited accuracy in the setting of SCA. The absence of ST-segment elevation does not exclude the presence of critical coronary stenoses. In approximately 50% of OHCA survivors despite the absence of ST-segment elevation in the post-arrest ECG, significant coronary artery stenosis can be found; However, even though these coronary artery stenoses were regarded “significant”, it remains unclear whether these stenoses are actually the cause for the cardiac arrest and whether revascularising these lesions can improve the clinical outcome. Unfortunately, the evidence in this area is very scant, cardiac arrest patients have been excluded from most acute myocardial infarction trials, which has created a gap of evidence for these patients. While non-cardiac arrest patients with ST-elevation infarctions clearly benefit from immediate angiography/ PCI, we lack data for patients after a cardiac arrest.

Conclusion

There have been multiple recent advances in the care of OHCA patients which may have a synergistic effect. The development of cardiac arrest centres, post-OHCA management protocols, further advances in therapeutic hypothermia, and primary percutaneous intervention (PPCI) in post-OHCA are likely to further improve outcomes in the future. We are moving away from the perception that survival of OHCA victims is a fortunate rare event towards a renewed sense that OHCA is often a treatable event with an increasing chance for neurologically intact survival.

Dr. Sundar Chidambaram

Consultant Interventional Cardiologist and Endo Vascular Specialist

Out-of-hospital cardiac arrest