In our last blog we discussed a case of cardiac arrest caused by blunt trauma. In this blog we will look at this cause of cardiac arrest in more details and a few other causes known as the Ts. See our previous blog for the Hs which are other causes of reversible cardiac arrest.
T – toxins – various toxins can cause irregular heart rhythms and result in cardiac arrest. Often history is extremely important in these cases to gain an insight into what toxin was consumed in order to give an appropriate antidote.
T – tamponade (cardiac) – this is where blood or another fluid builds up in the pericardium and puts pressure on the heart so that it is not able to beat. This can be recognised clinically by a triad of muddled heart sounds, distended neck veins and a narrowing pulse pressure (decreasing difference in the systolic and diastolic blood pressures). The treatment for this is to insert a needle into the pericardium in order to drain off the fluid. If indicated this can be done in an open chest after an emergency thoracotomy has been performed
T – tension pneumothorax – This is where there is a build-up of pressure between the plural layer that coats the lung and the one that sits inside the chest wall. The pressure builds so much that it shifts the mediastinum to the other side of the thorax. This can cause the great vessels of the heart to become kinked, limited the blood return to the heart. This is relieved by a needle thoracotomy, where a needle catheter is inserted into the 2nd intercostal space at the mid-clavicular line which relieves the pressure in the pleural cavity.
T – thrombosis (myocardial infarction) – a heart attack or myocardial infarction is where a clot has blocked the circulation within the coronary arteries, the vessels that supply the cardiac muscle itself with blood in order for it to pump. This is commonly due to atherosclerosis, where cholesterol deposits within the wall of the arteries, building into a plaque until eventually the lining ruptures. This rupture of the lining causes platelets to form a clot on the top of this break. The blood flowing past this clot can push it down into a smaller lumen where it blocked the artery completely.
T – thromboembolism (pulmonary embolism) – this is a clot in the pulmonary circulation of the heart, in a branch of the pulmonary artery. This prevents blood from getting to an area of the lung in order to be ventilated. To cause cardiac arrest these emboli are generally extremely large. The treatment for this is to administer thrombolytic medications and sometimes to perform a thrombectomy.
T – trauma – cardiac arrest can occur after a hard blow to the chest at a precise moment in the cardiac cycle (commotio cordis) or if there is significant structural damage to the chest contents. Commotio cordis is a form of ventricular fibrillation and isn’t causes by mechanical damage to the heart. The window of risk for this condition is a blow to the pericardial region during the start of the T wave on a ECG, which corresponds to the repolarisation of the ventricles. This is an extremely small window so the chances of it occurring are very small. The cellular mechanism for why this occurs is poorly understood. It is thought to be due to activation of mechanosensitive ion channels, which are triggered giving extra electrical excitation waves, which if occurring at the start of the repolarisation phase of the ventricles can result in ventricular fibrillation.
Being in accident and emergency has really put it into perspective that medicine is a constant learning curve and having the knowledge isn’t just for exams it’s for when you’re in a situation where that knowledge ends up saving someone’s life.