Not Just Hs and Ts Anymore—Meet the 5 Cs That Could Save a Life. Will the AHA 2025 Guidelines Finally Make It Official?
Prof. Tamorish Kole
Global Emergency Medicine Leader | Past President, Asian Society for Emergency Medicine | Physician | Educator | Patient Safety Champion | Health System Strengthening Advocate
Cardiac arrest remains one of the most urgent medical emergencies, where seconds count and decisions save lives. For decades, clinicians have relied on the mnemonic “Hs and Ts” to recall reversible causes during resuscitation. While this framework has stood the test of time, growing evidence suggests it no longer covers the full spectrum of clinically relevant causes—especially in younger patients, athletic populations, and those with neurologic conditions.
Recent studies and expert consensus have called for an expanded approach to better reflect the real-world complexity of cardiac arrest. Enter the 5 Cs—a fresh, evidence-informed addition that extends our diagnostic thinking and aims to close critical gaps in care. As the 2025 AHA Guidelines approach, this broader lens is likely to become central to how we teach, detect, and treat cardiac arrest.
The Foundation: Hs and Ts Revisited
The “Hs and Ts” framework is deeply embedded in ACLS training, offering a structured approach to uncover reversible causes of cardiac arrest.
The classic Hs include
H1: Hypoxia
H2: Hypovolemia
H3: Hydrogen ion (acidosis)
H4: Hypo-/Hyperkalemia
H5: Hypothermia
The Ts include
T1: Tamponade (cardiac)
T2: Tension pneumothorax
T3: Toxins
T4: Thrombosis (coronary)
T5: Thrombosis (pulmonary)
While this model captures the majority of common causes, it falls short in accounting for non-traditional or overlooked etiologies, particularly those seen in neurologic emergencies, inherited syndromes, or previously undiagnosed cardiac conditions.
Hypoglycemia is also (increasingly recognized as a distinct entity)
The Missing Pieces: Introducing the 5 Cs
To fill these gaps, clinicians and researchers have proposed the addition of the 5 Cs of Cardiac Arrest—a group of causes that are well-documented but not explicitly named in traditional teaching models. These are Cerebral causes, Cardiomyopathy, Conduction abnormalities, Congenital anomalies, and Commotio cordis.
C1: Cerebral Causes
One of the most under-recognized triggers of cardiac arrest is acute neurologic catastrophe, especially subarachnoid hemorrhage (SAH). Cerebral-origin arrests are often misdiagnosed as primary cardiac events due to ECG changes such as AV blocks, ventricular tachycardia, or asystole. In reality, these are the result of a massive sympathetic discharge following brain injury. Recognizing cerebral causes is critical, particularly in patients who collapse after headache, seizure, or neurologic symptoms.
C2: Cardiomyopathy
Hypertrophic, dilated, or restrictive cardiomyopathies are common culprits in sudden cardiac death (SCD) among young adults and athletes. Often undiagnosed until after an arrest, these conditions can result in electrical instability, pump failure, or arrhythmia. Diagnosis post-ROSC using echocardiography or cardiac MRI can guide further treatment and prevent recurrence in survivors or their family members.
C3: Conduction Abnormalities
Disorders such as Long QT syndrome, Brugada syndrome, and Wolff-Parkinson-White are examples of inherited conduction defects that predispose patients to lethal arrhythmias. These syndromes may present as cardiac arrest in individuals with no prior history of cardiac disease. Early ECG analysis, especially after ROSC, is essential for diagnosis. Management often includes implantable cardioverter-defibrillators (ICDs) and family screening.
C4: Congenital Heart Disease
Congenital cardiac anomalies—such as coronary artery anomalies or uncorrected septal defects—can go undetected for years, even in previously healthy individuals. They are among the leading causes of exertion-related cardiac arrest in children and adolescents. In emergency settings, rapid assessment with point-of-care ultrasound and history from family or prior records can help uncover these hidden threats.
C5: Commotio Cordis
Commotio cordis is a unique, trauma-induced cause of cardiac arrest, typically seen in young athletes. A blunt impact to the chest—usually during sports—delivered at a critical moment in the cardiac cycle can trigger ventricular fibrillation without any structural heart damage. Despite its rarity, it’s the second most common cause of sudden cardiac death in young athletes after hypertrophic cardiomyopathy. Immediate defibrillation is vital for survival.
Detection of the 5 Cs during Resuscitation
While active resuscitation focuses on high-quality CPR, airway management, and defibrillation, astute Emergency Physicians can begin to suspect the 5 Cs through clinical context, rapid assessments, and targeted bedside tools. For instance, Commotio cordis is suspected when a young athlete collapses after chest trauma; cerebral causes may be considered when arrest is preceded by seizure or sudden headache. Conduction abnormalities like Brugada or Long QT may be suggested by pre-arrest ECGs, if available, or during rhythm monitoring. Cardiomyopathy can sometimes be detected using point-of-care ultrasound (POCUS) to identify structural abnormalities such as a thickened septum or dilated ventricles. Gathering collateral history from bystanders or EMS can also provide critical clues, especially for congenital anomalies or prior unexplained syncope.
Detection After ROSC in the ED
Following return of spontaneous circulation (ROSC), the Emergency Department becomes a crucial zone for confirming and characterizing the underlying cause. A 12-lead ECG should be obtained immediately to detect conduction disorders, ST changes, or arrhythmogenic patterns. A focused bedside echocardiogram or cardiac POCUS can evaluate for cardiomyopathy, tamponade, or congenital structural issues. If cerebral causes are suspected, early non-contrast CT brain is essential. For congenital and inherited disorders, the ED team should initiate family history screening and arrange for downstream genetic or electrophysiology consultation. Even in high-acuity settings, integrating these evaluations early can transform acute care into long-term prevention for both the patient and their family.
The Road Ahead: What to Expect from the 2025 AHA Guidelines
The upcoming 2025 AHA Guidelines, scheduled for release in October 2025, are expected to reflect these evolving understandings of cardiac arrest pathophysiology. With mounting evidence from both emergency medicine and cardiology, it is anticipated that the guidelines will officially incorporate the 5 Cs into their framework, alongside the traditional Hs and Ts. This integration would signal a shift toward more individualized, cause-specific resuscitation strategies.
Additionally, the 2025 update may introduce refined algorithms for post-ROSC care, new recommendations on early neuroimaging, broader use of ECG and point-of-care ultrasound, and expanded criteria for family genetic screening in inherited cardiac syndromes. If implemented, these changes could mark a significant evolution in cardiac arrest management—from protocol-driven resuscitation to precision-guided revival and recovery.
Summary Mnemonic
5Hs: Hypoxia, Hypovolemia, Hydrogen ion, Hypo-/Hyperkalemia, Hypothermia. 5Ts: Tamponade, Tension Pneumothorax, Toxins, Thrombosis (Coronary/Pulmonary) 5Cs: Cerebral causes, Cardiomyopathy, Conduction abnormalities, Congenital heart disease, Commotio cordis
References
Introducing the C’s in CPR (2022)
NEW Causes of Cardiac Arrest You NEVER Thought Of?! Meet The Hs & Ts & Cs! (2024)
2025 AHA Guidelines Release Date (2025)
Director Medical Services and Director Anaesthesia and Critical care CKA BIRLA Hospital, Punjabi Bagh, New Delhi 110026.
1moThanks for sharing, Prof. Tamorish, very insightful.
Senior Consultant at Aakash Healthcare Super Speciality Hospital
1moThanks for sharing, Prof. Tamorish sir! Its a new revelation into the causes of cardiac arrest. This would help the teamleader establish a diagnosis.
Specialist Paramedic (Critical Care)
1moThe 5 Cs presented are pathologies that can result in cardiac arrest, not reversible causes of it. The Hs & Ts are pathophysiological mechanisms that can (sometimes) be quickly reversed with the correct intervention. Two different things, no?
Director, Medical Operations at Healthspring - Family Health Experts - - - Fellow, Royal Society of Medicine
1moWell put, Prof. Tamorish