The Importance of Cardiac Arrest Rhythms

Synopsis Provided By

Sabrina Hoehne, Dr. med vet.,Dipl. ACVECC, Sipl. ECVECC

https://onlinelibrary.wiley.com/doi/10.1111/vec.13320

Synopsis

Why is ECG monitoring and correct cardiac rhythm diagnosis so important during CPR? While basic life support interventions are shared among all CPR efforts, appropriate advanced life support interventions depend on whether a patient displays a shockable or a non-shockable cardiac arrest rhythm.

Cardiac Arrest Rhythms in People

In people, the initial cardiac arrest rhythm during CPR is one of the factors most predictive of CPA patient outcome.¹ Initial cardiac arrest rhythms are significantly more commonly non-shockable rhythms than shockable rhythms, and several patient factors have been associated with the development of specific cardiac arrest rhythms.^2-4 Survival rates in patients with initial shockable cardiac arrest rhythms are significantly higher than in patients with initial non-shockable rhythms, and the availability of a causative therapeutic intervention – electrical defibrillation – is likely responsible for these more favorable outcomes.^5,6

Cardiac Arrest Rhythms in Small Animals

While less is known about cardiac arrest rhythms in small animals, it is apparent from information in people, that being aware of the prevalence and factors associated with shockable and non-shockable cardiac arrest rhythms can help the medical care team anticipate and prepare for the most appropriate advanced life support interventions and in turn potentially improve patient outcomes. A recent study by Vega et al. utilized the RECOVER CPR registry database to investigate cardiac arrest rhythms in dogs and cats. The study analyzed cardiac arrest rhythms of 457 dogs and 170 cats that underwent CPR at 16 academic and private veterinary hospitals.⁷ Similar to people, the most commonly encountered initial cardiac arrest rhythms in dogs and cats were non-shockable, while ventricular fibrillation and pulseless ventricular tachycardia cumulatively only accounted for <5% of rhythm diagnoses.⁷

Fifteen percent of animals with an initial non-shockable cardiac arrest rhythm in the study converted to a shockable cardiac arrest rhythm during the course of CPR.7 Factors significantly associated with patients displaying an initial shockable rhythm included a metabolic causes of arrest (OR 7.6; 95%CI 2.41-24.0), while higher body weight (OR, 1.03; 95%CI 1.00-1.05), hemorrhagic cause of arrest (OR 2.84; 95%CI 1.29-6.27), and intracranial disease as the cause of arrest (OR 3.73; 95%CI 1.31-10.6) were significantly associated with rhythm conversion to a subsequent shockable rhythm.⁷

Vega et al. further report that thirty-five percent of dogs and 37% of cats with initial shockable cardiac arrest rhythms achieved return of spontaneous circulation (ROSC) and 5% of dogs and no cats survived to hospital discharge.⁷ In comparison, 25% of dogs and 31% of cats with initial non-shockable cardiac arrest rhythms achieved ROSC, 3% of dogs and 2% of cats survived to hospital discharge.⁷ While their study was unable to demonstrate a significant difference in ROSC rates between animals with initial or subsequent shockable and those with non-shockable cardiac arrest rhythms, one previous single center veterinary study with a higher prevalence of initial shockable cardiac arrest rhythms found a higher ROSC rate in dogs (but not cats) with initial shockable cardiac arrest rhythms that were promptly electrically defibrillated. The prevalence of initial shockable cardiac arrest rhythms in that previous study was 21% in dogs and 16% in cats – higher than subsequently observed in Vega’s multicenter study. Based on the lower prevalence of shockable cardiac arrest rhythms across multiple veterinary centers, the Vega study was likely underpowered to conclusively demonstrate differences in patient outcomes between shockable and non-shockable cardiac arrest rhythms. The lack of an association between rhythm diagnosis and ROSC rates in the Vega study should therefore be interpreted with caution and outcome analyses repeated once the RECOVER registry data set has grown to include more patients with shockable cardiac arrest rhythms.

Until such time, electrical defibrillation remains the mainstay of treatment for shockable cardiac arrest rhythms in dogs and cats. It is advisable for veterinary centers to be equipped with an ECG and an electrical defibrillator to be able to recognize and provide adequate care to patients with shockable cardiac arrest rhythms. Based on the study by Vega et al., this seems particularly important if a practice sees a high emergency patient case load, or frequently cares for patients with metabolic alterations, hemorrhage, or intracranial diseases.

References

1. Andersen LW, Holmberg MJ, Berg KM, Donnino MW, Granfeldt A. In-Hospital Cardiac Arrest: A Review. JAMA. 2019;321(12):1200-1210. doi:10.1001/jama.2019.1696
2. Tsao CW, Aday AW, Almarzooq ZI, et al. Heart Disease and Stroke Statistics-2022 Update: A Report From the American Heart Association. Circulation. 2022;145(8):e153-e639.doi:10.1161/CIR.0000000000001052
3. Stankovic N, Høybye M, Holmberg MJ, Lauridsen KG, Andersen LW, Granfeldt A. Factors associated with shockable versus non-shockable rhythms in patients with in-hospital cardiac arrest. Resuscitation. 2021;158:166-174. doi:10.1016/j.resuscitation.2020.11.022
4. Hoehne SN, Hopper K, Epstein SE. Prospective Evaluation of Cardiopulmonary Resuscitation Performed in Dogs and Cats According to the RECOVER Guidelines. Part 2: Patient Outcomes and CPR Practice Since Guideline Implementation. Front Vet Sci. 2019;6:439.doi:10.3389/fvets.2019.00439
5. Nolan JP, Soar J, Smith GB, et al. Incidence and outcome of in-hospital cardiac arrest in the United Kingdom National Cardiac Arrest Audit. Resuscitation. 2014;85(8):987-992.doi:10.1016/j.resuscitation.2014.04.002
6. Chan PS, McNally B, Tang F, Kellermann A, CARES Surveillance Group. Recent trends in survival from out-of-hospital cardiac arrest in the United States. Circulation.2014;130(21):1876-1882. doi:10.1161/CIRCULATIONAHA.114.009711
7. Vega Suarez L, Epstein SE, Martin LG, Davidow EB, Hoehne SN, the RECOVER CPR Registry Consortium. Prevalence and factors associated with initial and subsequent shockable cardiac arrest rhythms and their association with patient outcomes in dogs and cats undergoing cardiopulmonary resuscitation: A RECOVER registry study. J Vet Emerg Crit Care. Published online August 12, 2023:vec.13320. doi:10.1111/vec.13320