Why is pulsus paradoxus (abnormal decrease in systolic blood pressure during inspiration) more commonly seen in cardiac tamponade than in constrictive pericarditis?

From the Guidelines

Pulsus paradoxus is more commonly seen in cardiac tamponade than in constrictive pericarditis due to the fundamental differences in their pathophysiology, with cardiac tamponade causing a significant drop in systolic blood pressure during inspiration due to increased venous return to the right heart and subsequent reduction in left ventricular filling and stroke volume. In cardiac tamponade, fluid rapidly accumulates in the pericardial space, creating increased pressure that compresses the heart chambers, as described in the European Heart Journal by 1. During inspiration, negative intrathoracic pressure increases venous return to the right heart, causing the interventricular septum to bulge into the left ventricle. This, combined with the fixed pericardial volume from effusion, significantly reduces left ventricular filling and stroke volume during inspiration, resulting in a marked drop in systolic blood pressure (pulsus paradoxus). Some key points to consider in the diagnosis of cardiac tamponade include:

• Elevated systemic venous pressure, hypotension, pulsus paradoxus, tachycardia, and dyspnea or tachypnea with clear lungs, as outlined in the European Heart Journal by 1
• Precipitating factors such as drugs, recent cardiac surgery, indwelling instrumentation, blunt chest trauma, malignancies, connective tissue disease, renal failure, and septicemia
• ECG changes, including electrical alternans, bradycardia, and electromechanical dissociation
• Chest X-ray findings, such as an enlarged cardiac silhouette with clear lungs
• M-mode/2D echocardiogram findings, including diastolic collapse of the right ventricular free wall, right atrial collapse, and increased left ventricular diastolic wall thickness In contrast, constrictive pericarditis involves a thickened, fibrotic pericardium that limits overall cardiac filling but does so more equally throughout the respiratory cycle, as discussed in the European Heart Journal by 1. The rigid pericardial shell in constrictive pericarditis prevents the normal inspiratory increase in right heart filling that would otherwise cause ventricular interdependence, thus minimizing respiratory variation in blood pressure. Additionally, in constrictive pericarditis, the dissociation between intrathoracic and intracardiac pressures is less pronounced than in tamponade, further reducing the likelihood of significant pulsus paradoxus. The most recent and highest quality study, published in the European Heart Journal by 1 in 2020, highlights the importance of pre-hospital risk assessment and echocardiography in the diagnosis of cardiac tamponade. The study emphasizes the need for continuous ECG monitoring and venous access in all patients with cardiac arrhythmias and the prompt treatment of supraventricular and ventricular arrhythmias associated with hemodynamic instability. Overall, the pathophysiological differences between cardiac tamponade and constrictive pericarditis, as well as the diagnostic findings and management strategies, highlight the importance of accurate diagnosis and treatment in these conditions.

From the Research

Pulsus Paradoxus in Cardiac Tamponade and Constrictive Pericarditis

• Pulsus paradoxus is an abnormal decrease in systolic blood pressure during inspiration, commonly seen in cardiac tamponade 2, 3, 4, 5, 6.
• The mechanism of pulsus paradoxus in cardiac tamponade is due to reduced filling of the left ventricle during inspiration, resulting from increased right heart filling and decreased left ventricular dimensions 2, 3, 5.
• In cardiac tamponade, the pericardial fluid compresses the heart, leading to reduced left ventricular end-diastolic volume and decreased left ventricular filling pressure 2, 4.
• Pulsus paradoxus is a relatively late phenomenon in cardiac tamponade, occurring with severe tamponade and associated with an inspiratory decrease in left atrial and ventricular volumes 2, 4.

Comparison with Constrictive Pericarditis

• Constrictive pericarditis is a condition where the pericardium becomes stiff and fibrotic, restricting diastolic filling of the heart 6.
• Pulsus paradoxus is less common in constrictive pericarditis compared to cardiac tamponade, as the stiff pericardium restricts ventricular filling and prevents the excessive respiratory variation in ventricular volumes seen in tamponade 4, 6.
• The presence of pulsus paradoxus greater than 10 mm Hg in a patient with a pericardial effusion increases the likelihood of tamponade, while a pulsus paradoxus of 10 mm Hg or less greatly lowers the likelihood 6.

Key Findings

• Inspiratory increases in right heart filling and output are necessary for pulsus paradoxus to occur 3, 5.
• Doppler studies of pulmonary venous inflow confirm that an inspiratory fall in left atrial filling is necessary for pulsus paradoxus 3.
• Pulsus paradoxus is complex and multifactorial in origin, and may be absent in cardiac tamponade when certain conditions coexist, such as left ventricular dysfunction 3, 4.