2.7 Reversible Causes of Arrest: The T's

2.7 Reversible Causes of Arrest: The T's

Continuing the evaluation of reversible causes during cardiac arrest, the "T's" encompass a range of traumatic, toxicological, and thromboembolic emergencies. These conditions frequently present as pulseless electrical activity (PEA) or asystole. Because standard CPR and epinephrine cannot correct the underlying structural or chemical defects associated with the T's, rapid clinical diagnosis and targeted mechanical or pharmacological interventions are mandatory for survival.

Toxins

Toxicological emergencies are an increasingly common cause of cardiac arrest, largely driven by the opioid epidemic and polypharmacy in patients with psychiatric or cardiac comorbidities. Recognition relies on collateral history from bystanders, evidence at the scene (e.g., pill bottles, drug paraphernalia), and recognizing specific toxidromes prior to the arrest.

• Opioids: Severe respiratory depression leads to hypoxia and subsequent cardiac arrest. If suspected, the administration of naloxone (an opioid antagonist) is critical. While standard CPR takes precedence, naloxone can be given IV, IO, intramuscularly, or intranasally.
• Tricyclic Antidepressants (TCAs): TCA overdose causes profound sodium channel blockade in the heart, leading to widening of the QRS complex, ventricular dysrhythmias, and hypotension. The primary antidote and stabilizing agent is sodium bicarbonate, which overcomes the blockade and alkalinizes the serum.
• Beta-Blockers and Calcium Channel Blockers (CCBs): Overdose of these agents results in refractory bradycardia, hypotension, and eventually cardiovascular collapse. While standard ACLS drugs may be ineffective, high-dose glucagon (which bypasses the beta-receptor to increase intracellular cAMP) is a primary treatment for beta-blocker toxicity. Calcium chloride or gluconate, along with high-dose insulin therapy, is utilized for CCB overdose.
• Local Anesthetic Systemic Toxicity (LAST): Caused by inadvertent intravascular injection of local anesthetics like bupivacaine, leading to neurotoxicity and cardiac arrest. The specific antidote is the administration of 20% intravenous lipid emulsion, which acts as a "lipid sink" to draw the drug out of myocardial tissue.

Tamponade (Cardiac)

Cardiac tamponade occurs when fluid (blood or effusion) rapidly accumulates in the pericardial sac. Because the pericardium is inelastic, this fluid exerts immense pressure on the heart, restricting ventricular filling during diastole. This leads to a precipitous drop in preload, severely reduced cardiac output, and eventually PEA. Tamponade can result from penetrating chest trauma, rupture of the ventricular wall post-myocardial infarction, or malignant effusions.

Clinical signs prior to arrest include Beck's triad: hypotension, jugular venous distention (JVD), and muffled heart sounds. However, in an actively arresting patient, these signs are impossible to reliably assess. Point-of-care ultrasound (POCUS) is the gold standard for rapid diagnosis during CPR pauses, visualizing an anechoic (black) stripe around the heart and right ventricular diastolic collapse. The definitive emergency treatment is pericardiocentesis—inserting a needle through the chest wall (often subxiphoid) into the pericardial sac to aspirate the fluid. Removing even 20 to 50 mL of fluid can dramatically improve hemodynamics and facilitate ROSC.

Tension Pneumothorax

A tension pneumothorax develops when air enters the pleural space (usually from a lung laceration or ruptured bleb) but cannot escape. As pressure builds, it completely collapses the affected lung and shifts the mediastinum away from the injury. This shift compresses the superior and inferior vena cava, drastically reducing venous return to the heart, leading to PEA.

Clues to a tension pneumothorax include severe respiratory distress prior to arrest, unequal chest rise, absence of breath sounds on the affected side, and hyperresonance to percussion. Tracheal deviation is a very late and often unreliable sign. In the setting of cardiac arrest, especially if the patient is receiving positive pressure ventilation (which exacerbates the condition), treatment must be immediate. The intervention is a needle decompression. A large-bore catheter (14-gauge or larger) is inserted into the pleural space to vent the trapped air. The traditional anatomical landmark is the 2nd intercostal space at the midclavicular line, though the 5th intercostal space at the anterior axillary line is increasingly recommended due to a higher success rate in reaching the pleural space in patients with thicker chest walls. This must be followed up with definitive chest tube placement.

Thrombosis (Coronary)

Coronary thrombosis refers to an acute myocardial infarction (MI) caused by the rupture of an atherosclerotic plaque and subsequent clot formation, completely occluding a coronary artery. This ischemia leads to massive myocardial necrosis and electrical instability, frequently presenting as VF or pVT.

Diagnosing coronary thrombosis during an arrest is challenging unless an ECG showing ST-segment elevation was obtained before the arrest occurred. If a patient achieves ROSC, obtaining a 12-lead ECG is the highest priority. If ST-segment elevation myocardial infarction (STEMI) is identified, the patient requires emergent activation of the cardiac catheterization lab for percutaneous coronary intervention (PCI). In select centers, patients who remain in refractory cardiac arrest suspected to be of coronary origin may be placed on extracorporeal cardiopulmonary resuscitation (ECPR/ECMO) to maintain perfusion while they are transported to the cath lab for mechanical revascularization.

Thrombosis (Pulmonary)

Pulmonary thrombosis, or a massive pulmonary embolism (PE), occurs when a large blood clot lodges in the main pulmonary artery or its major branches. This creates a massive obstruction to right ventricular outflow, leading to acute right heart failure, lack of blood reaching the left heart, and sudden cardiovascular collapse (typically PEA). Risk factors include recent surgery, prolonged immobilization, active cancer, or a known deep vein thrombosis.

Diagnosis relies heavily on clinical history or the use of POCUS during CPR to identify acute right ventricular dilation. When massive PE is highly suspected or confirmed as the cause of cardiac arrest, standard CPR is often ineffective due to the mechanical obstruction. The administration of systemic fibrinolytic therapy (such as alteplase or tenecteplase) during the arrest is considered. Because fibrinolytics require time to break down the clot, the ACLS guidelines recommend that if these drugs are given, CPR should be continued for an extended period (often at least 60 to 90 minutes) to allow the medication time to work.