Cardiac tamponade

Cardiac tamponade is compression of the heart due to fluid accumulation within the pericardial space. When fluid or blood accumulates within in the pericardial cavity, the intra-pericardial pressure rises and compresses the heart. The lower pressure atria are most vulnerable to this increased pressure; their compression leads to impaired venous return and decreased cardiac filling. Compression of the heart as a whole also impairs diastolic filling.

Surgical causes include penetrating cardiac wounds, blunt trauma to the chest, or post-operative accumulation after open heart surgery. Tamponade can also occur as a complication of central line placement. Medical causes include malignancy, pericarditis, post-MI ventricular rupture, and uremia.

Clinical presentation and diagnosis

Presentation may be acute when fluid or blood accumulates in the heart very rapidly or it may be late when the rate of fluid accumulation is slow and compression occurs only after a period of time. Beck's triad of muffled heart sounds, hypotension, and elevated jugular venous distension may be evident particularly in the acute setting. Hemodynamically compromised patients are tachycardic and hypotensive. In the acute setting, they may be sitting up and extremely anxious. Evidence of right heart failure with jugular venous distension and hepatomegaly may be apparent. Decreased heart sounds or a pericardial friction rub may be noted in up to a third of patients.

Pulsus parodoxus is a classic finding in patients with peri-cardial tamponade. It is defined as an exaggerated fall in arterial systolic pressure (>10mmHg) during inspiration (Fig. 8.7). Kussmaul described this 'paradox' by noting a disappearance of the pulse during inspiration, although the heartbeat was still audible. Here is how it works. During inspiration, intra-thoracic pressure falls and allows for increased venous return, and increased RV filling. However, in tamponade, because the heart is compressed and there is no room to accommodate the increased RV filling, the intra-ventricular septum becomes displaced to the left. The bulge of the septum inhibits LV filling, and as a result, stroke volume decreases with a subsequent decrease in cardiac output and arterial pressure.

In the acute setting, diagnosis should be suspected clinically. In a post-operative cardiac patient, hypotension, tachycardia, and low urine output should put the surgeon on instant alert. Diagnosis is now made quickly and easily with ultrasound. Bedside ultrasound is becoming increasingly available, even in Accident and Emergency (A&E) departments. In the absence of ultrasound, pericardiocentesis may be performed as a diagnostic and potentially therapeutic measure. Nevertheless, pericardiocentesis has associated risks (arrhythmias, cardiac laceration, coronary artery laceration, tamponade, and pneumothorax) and is ideally

Inspiration Expiration

Figure 8.7. Pulsus paradoxus. Arterial waveform of a patient with pulsus paradoxus. Note the exaggerated fall in systolic pressure (>10 mmHg) seen on inspiration.

Inspiration Expiration

Figure 8.7. Pulsus paradoxus. Arterial waveform of a patient with pulsus paradoxus. Note the exaggerated fall in systolic pressure (>10 mmHg) seen on inspiration.

performed only once pericardial fluid is confirmed or very highly suspected.

Management

Management involves draining the cause of tamponade. In a patient who has undergone cardiac surgery, emergent sternal re-opening and evacuation of blood may be life saving. Patients with penetrating chest wounds and tamponade should be taken for immediate sternotomy. Incidentally, these patients are rarely stable and often will require emergent thoracotomy (and opening of the pericardial sac) in A&E. Pericardiocentesis has a role in providing urgent symptomatic relief in tamponade due to more chronic conditions such as uremia or malignancy. It should be performed with the patient sitting up and a needle introduced just to the left of the xiphoid, at a 15° angle to the skin, and directed slowly toward the left shoulder. Ultrasound guidance is now the norm. Surgical creation of a 'window' or small hole in the pericardium to communicate with the pleural space is a useful option for draining chronic pericardial effusions causing tamponade.

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