Fonte: Rachel Liu, BAO, MBBCh, Emergency Medicine, Yale School of Medicine, New Haven, Connecticut, EUA
O coração está dentro do pericárdio, um saco fibroso relativamente inelástico. O pericárdio tem alguma conformidade para esticar quando o fluido é lentamente introduzido no espaço pericárdial. No entanto, o acúmulo rápido sobrecarrega a capacidade pericárcial de acomodar fluido extra. Uma vez que um volume crítico é atingido, a pressão intraperiárdia aumenta drasticamente, comprimindo o ventrículo direito e eventualmente impedindo o volume que entra no ventrículo esquerdo. Quando essas câmaras não conseguem preencher diastole, o volume de derrame e a saída cardíaca são diminuídos, levando ao tampono cardíaco, uma compressão fatal das câmaras cardíacas por um derrame pericárdico. A menos que a pressão seja aliviada pela aspiração de fluido pericárdico (pericardiocentesis), a parada cardíaca é iminente.
Tamponade cardíaco é uma emergência crítica que pode levar alta morbidade e mortalidade. Os pacientes podem se apresentar nos extremos, sem muito tempo para fazer o diagnóstico e realizar tratamentos que salvam vidas. As causas dessa condição são divididas em categorias traumáticas e não traumáticas, com diferentes algoritmos de tratamento. Facadas e ferimentos de bala são a principal causa de tamponade traumático, mas pode ocorrer por traumatismo craniano associado a fraturas severas ou costelas, bem como corte de vasos de lesões de desaceleração rápida. Causas não traumáticas incluem ruptura da base aórtica aórtica de dissecção aórtica ascendente, ruptura do miocárculo do ventrículo após infarto do miocárdio, hemorragia espontânea de medicação trombolítico ou anticoagulante, e derrames criados por infecção ou câncer.
Efusões crônicas de crescimento lento geralmente não são fatais, mesmo as grandes. O pericárdio tem se estendido gradualmente para incorporar litros de fluido em alguns casos. Estes podem ser tratados com pericardiocentesis eletivas sob orientação fluoroscópica, ou uma janela pericárdia. No entanto, a transição para a fisiologia tamponada com um paciente em extremidades requer pericardiocentesis urgentes, mesmo com uma pequena quantidade de fluido. O tamponado apresenta um desafio para diagnosticar, pois seus sintomas e achados físicos são muitas vezes inespecíficos, comuns a uma série de doenças. Um eletrocardiograma (ECG ou ECG) pode mostrar alternados elétricos, e um raio-x do peito pode mostrar uma silhueta cardíaca “garrafa de água” aumentada.
Tamponade should always rank highly in the diagnoses for undifferentiated shock, particularly in patients with prior cardiac disease, suspected aortic dissection, a history of malignancy, or anticoagulant use. Traumatic tamponade must be considered in both penetrating and blunt trauma scenarios, with temporizing pericardiocentesis performed in deteriorating patients while setting up for thoracotomy. High suspicion, clinical vigilance, understanding of tamponade physiology, and prompt action will help to avoid the deadly effects of this process.
In this modern age when imaging guidance is more prevalent, complications from deep or inappropriate needle insertion may be prevented. Patients requiring emergent pericardiocentesis often cannot sustain the time required to obtain fluoroscopy-guided or computed tomography (CT)-guided pericardiocentesis. However, bedside ultrasound is immediately available in many emergency departments and is a necessary adjunct to performing procedure. Needle entry into pericardial fluid can be viewed in real time, as well as real time aspiration. Placement in the appropriate location can be rapidly confirmed using agitated saline. Absence of pneumothorax or hemothorax can be rapidly assessed. Real time viewing also allows a better approach plan, providing more operator comfort in performing apical or parasternal approaches and thus improving success.
Pericardiocentesis has some complications that may become major. These include cardiac puncture or coronary vessel laceration, liver or stomach laceration, pneumothorax, hemothorax, pneumoperitoneum, pneumopericardium, suppurative pericarditis, and pulmonary edema due to sudden venous return to the left ventricle. Serious dysrhythmias are not common and may be vagal mediated. This may be prevented by giving atropine prior to the procedure. Failure of pericardiocentesis to yield fluid may be considered a complication, and is much more common in the blind approach.
Pericardiocentesis – the aspiration of fluid from the space between the heart and pericardium – is a potentially lifesaving procedure performed to relieve cardiac tamponade.
Cardiac tamponade occurs when fluid collects rapidly in the pericardial space, causing a dramatic increase in pressure inside this space. If untreated, the fluid accumulation will lead to cardiac arrest.
This video will review the etiology and diagnosis of cardiac tamponade, demonstrate the technique of pericardiocentesis using EKG guidance, and discuss the possible complications of the procedure.
The pericardium is a relatively inelastic fibrous sac, which surrounds the heart. If fluid accumulates slowly in the space between the pericardium and the heart – such as due to infection or cancer – the sac can stretch to accommodate it. However, a rapid accumulation of fluid in the pericardial space causes compression of the ventricles, which leads to decreased cardiac filling, diminished stroke volume, reduced cardiac output, and ultimately, cardiac arrest.
The reason behind cardiac tamponade could be non-traumatic, such as malignancy, myocardial infarction, or bleeding due to an anticoagulant medication. Or the cause could be traumatic like stabbings, or sternal or rib fractures.
Cardiac tamponade can be difficult to diagnose, as many of the findings are non-specific. Signs on physical exam include: diaphoresis, agitation, distended neck veins, an inability to lie flat, tachypnea, inability to speak full sentences and cyanosis. The patient may also be tachycardic, and upon auscultation of the chest wall, there will be muffled heart sounds. Also, the point of maximal impulse felt by palpation might be displaced. The patient may also be hypotensive and have a narrow pulse pressure. Or they may present with pulsus paradoxus, which is a decrease of the systolic blood pressure by more than 10 mm Hg during inspiration.
The EKG may demonstrate electrical alternans, which is an inconsistency in the height of the QRS complex. Also a chest X-ray may show an enlarged – or “water bottle” cardiac silhouette. A bedside echocardiography, if available, will demonstrate fluid in the pericardial space compressing the right ventricular wall during diastole.
Now that we have discussed the etiology and diagnoses for cardiac tamponade, lets review the protocol for pericardiocentesis under EKG guidance. Note that this can be performed blind or under ultrasound guidance as well.
Start by gathering the necessary equipment onto a sterile tray. This includes: a 60 cc syringe, a 18-gauge spinal needle, 1% Lidocaine, an alligator clip cable, a guidewire, a dilator, an 8 French pigtail catheter, an EKG machine, and suture, gauze and tape. Before starting the procedure on an obtunded patient, they should be stabilized with IV fluid boluses and may need vasopressors to support the blood pressure. Although intubation may be necessary, be aware that positive pressure in the thorax might place even more strain on the heart wall.
To begin the procedure, position the patient with their chest elevated to a 45° angle and ensure that the cardiac monitor is attached. If not intubated, administer oxygen via nasal cannula or a non-rebreather mask and give IV fluids. This procedure is most commonly performed via the sub-xiphoid approach. Therefore, start by cleansing the subxiphoid and epigastric region with betadine and place sterile drapes around the area. Note that the insertion site is 1 cm inferior to the xiphoid and the needle will be initially aimed toward the left shoulder. Anesthetize the skin and subcutaneous tissue along this path using 1% Lidocaine. Then, connect the spinal needle to the 60 cc syringe. Also, attach a precordial EKG lead located on the patient’s chest to the hub of the spinal needle using the alligator clip cable and start recording a rhythm strip from this lead.
Insert the spinal needle 1 cm below the xiphoid process and advance the needle slowly, aiming toward the left shoulder. Hold it at a 30° angle to the skin to avoid injuring the structures behind the heart. The depth of insertion depends on the individual’s habitus. Aspirate continually while the needle is being advanced and monitor the EKG strip. If there is no fluid return, withdraw the needle and re-direct it at a higher angle to the skin. If there is still no fluid, withdraw the needle and reinsert it at the same angle, aiming slightly more towards the mid-line. Continue to redirect the needle until fluid is aspirated. This might even require aiming the needle towards the right shoulder.
Once fluid enters the syringe, do not advance the needle any further. Note that the patient might experience sharp chest pain when the pericardium is pierced. If the tip of the needle touches the epicardium, the EKG will show an injury pattern that looks like a wide-complex PVC with ST elevation. If this occurs, withdraw the needle to prevent laceration of the myocardium. If the patient is in extremis, aspirate as much fluid at this point as possible, as this may result in rapid clinical improvement. Then, stabilize the needle to prevent it from penetrating further and remove the syringe from the needle.
The next step is to thread the guidewire through the spinal needle into the pericardial space, and remove the needle. Pass the dilator over the wire to dilate the subcutaneous tissue and then remove the dilator, leaving the guidewire in place. Next, pass the pigtail catheter over the guidewire and remove the guidewire. Now aspirate the fluid through the catheter and at the end place a stopcock on the catheter to allow for future aspiration of fluid. Laslty, cover the entrance site with gauze and tape and suture the free end of the catheter to the skin. Obtain a chest x-ray to rule out pneumothorax or pneumopericardium.
The potential risks of pericardiocentesis include: cardiac puncture, coronary vessel laceration, liver or stomach laceration, pneumothorax, hemothorax, pneumoperitoneum, pneumopericardium, suppurative pericarditis, and pulmonary edema. Serious dysrhythmias can also occur, but because these may be vagally mediated, pretreating with Atropine may prevent them.
“Cardiac tamponade is a life-threatening condition, which should always be considered in patients with undifferentiated shock, particularly if there is a history of malignancy or anticoagulant use, cardiac disease or suspected aortic dissection. If not treated using pericardiocentesis, this condition can lead rapidly to the patient’s demise.”
You have just watched JoVE’s video on pericardiocentesis for the treatment of life-threatening cardiac tamponade. You should now have a better understanding of the pathophysiology, diagnosis and emergency treatment of this condition. As always, thanks for watching!
