The heart, vasculature, and blood (pump, pipes, and fluid) work together to meet the metabolic demands of the body. End organs and tissue are not adequately perfused when the system fails, leading to injury and deranged physiology. Understanding the hemodynamic relations in normal cardiovascular physiology and how it changes in pathologic conditions helps us make the correct diagnosis and implement the right treatment.
Physical examination can provide indirect clues to hemodynamics, though invasive evaluation has been the traditional gold standard. This can include arterial and central venous pressure measurements, cardiac right and left heart catheterization, or bedside pulmonary artery catheter. Fortunately, a rapidly expanding toolbox of noninvasive and minimally-invasive assessment methods has been developed that allow us to evaluate the hemodynamics of our patients without the risk associated with the invasive techniques. These include formal and bedside 2-D and Doppler echocardiography, arterial pulse contour analysis, transpulmonary thermodilution, electrical bioimpedance, and tissue oxygenation monitoring.
I am going to discuss three classic diseases — pericardial tamponade, constrictive pericarditis, and restrictive cardiomyopathy — over the next several months to explore the basics of cardiovascular hemodynamics and to develop an understanding of the methods used for evaluation.
A 58-year-old man presented to the emergency department with two days of exertional shortness of breath and chest pain. He described the pain as an 8/10 “tightness” originating in the epigastric region with radiation to both sides of his neck. It had been relatively constant since onset. It was associated with moderate shortness of breath but no other symptoms. The chest pain did not have an exertional component, but the shortness of breath did worsen with activity. The patient said he tired easily and had been sleeping more over the previous several months. He was not taking any medication and did not smoke.
His vital signs revealed mild tachycardia and tachypnea but normal blood pressure and temperature. He did not appear in distress, his lungs were clear, and an abnormal heart sound was present in diastole. No murmur was noted. He had a benign abdomen and moderate pedal edema. The remainder of his physical exam was unremarkable. Given his complaint of chest pain, a 12-lead electrocardiogram was immediately obtained, and is shown in Figure 1.
Figure 1. Presenting ECG.
The ECG shows atrial fibrillation with a ventricular rate of 75 bpm. A terminal R wave in V1 and S wave in the lateral leads, along with a normal QRS duration suggests incomplete right bundle branch block. Right precordial non-specific ST-segment and T-wave changes may indicate right ventricular hypertrophy.
An upright AP chest radiograph was obtained. (Figure 2.) The lung fields were clear, but extensive calcification was seen over the cardiac silhouette, and a calcified pleural band was seen in the right lower thorax. This prompted the emergency physicians to obtain a chest CT. (Figure 3.)
Figure 2. Plain AP chest radiograph.
Figure 3. Cross-sectional image from chest CT at level of the mitral valve.
The lung fields were clear on CT; no evidence was seen of a pulmonary embolism. What was striking, however, was thick calcified bands across the heart, most notably in the atrioventricular groove. This unusual finding is consistent with constrictive pericarditis. (Figure 4.)
Figure 4. Cross-sectional image from chest CT at level of superior atrioventricular groove.
If the infection or inflammatory process of acute pericarditis becomes chronic, it can cause fibrous thickening of the pericardium which eventually becomes calcified, severely reducing its compliance. This almost always occurs around the atrioventricular groove. Neoplastic disease causes constrictive pericarditis by tumor infiltration of the pericardium and pericardial space. Tuberculosis was once the leading cause of constrictive pericarditis, but it and other bacterial causes have fallen tremendously in the United States because of effective anti-infective treatment. A list of common causes is shown in the table. The largest category in the United States today is idiopathic, but it is believed that most of these originally originated from an infectious process. Constrictive pericarditis can also be seen as a complication many years after radiation therapy and cardiac surgery.
The symptoms of constrictive pericarditis develop insidiously, and early on they often are nonspecific complaints such as malaise, fatigue, and decreased exercise tolerance. As the constriction worsens, typical signs and symptoms of systemic congestion and decreased cardiac output develop. These may include peripheral edema, systemic venous congestion, ascites, hepatic congestion, portal hypertension, and pleural effusions.
These symptoms develop from the significant effects that constriction has on cardiac hemodynamics. The principle physiologic abnormality is impaired cardiac filling. The noncompliant pericardium decreases diastolic filling, increases intracardiac pressures, and isolates intracardiac pressures from intrathoracic pressures. The enclosed pericardial space prevents the normal distensibility of the myocardium by the transmural pressures, so end-diastolic pressures are equal in all four cardiac chambers. The reduced compliance of the pericardium also limits the end-diastolic volume of both ventricles, which leads to elevation of the filling pressures. The right and left atrial pressures are elevated in proportion to the degree of constriction. Right atrial pressure can reach 20-25 mm Hg in severe cases.
The ventricle size is smallest at the start of diastole, and the ventricular constriction is at its least at this time. The ventricles at the beginning of diastole expand normally, and rapid filling is limited to the first phase of diastole. Diastolic filling comes to an abrupt halt and ventricular filling pressures rise rapidly once the ventricles reach the confines of the pericardium. The myocardium itself is normal, and therefore systole is unimpaired.
The presence of a noncompliant pericardium limits the transmission of intrathoracic pressure to the heart. Negative intrathoracic pressure during inspiration is not communicated to the intrapericardium and the right heart in severe constriction. The normal fall in systemic venous and right atrial pressures is therefore not seen. The venous pressure can actually rise with inspiration in severe cases.
The pulmonary artery systolic pressure is typically only modestly elevated (34-45 mm Hg) in pericardial constriction while the diastolic pressure should equal right atrial pressure and the pulmonary artery occlusion pressure. The aortic pressure is usually maintained on the left side of the heart. Pulsus paradoxus is observed in only about a third of patients with pericardial constriction. The stroke volume index may be as low as 15-25 mL/m2 with severe constriction.
The history and initial workup may suggest constrictive pericarditis (as it does in this case), but confirming the diagnosis and the presence of constrictive physiology represents a challenge and ultimately depends on assessing the patient’s cardiovascular hemodynamics, indirectly or directly.
Physical examination can reveal general signs of reduced cardiac output and systemic congestion, but a focused examination can provide clues more specific to constrictive pericarditis. Cardiac auscultation can reveal muffled sounds. The mitral and tricuspid valves are nearly closed by end of diastole, so the S1 sound is diminished. An early diastole sound called a pericardial knock can be heard when there is significant constriction, but it is often difficult to distinguish from other diastole sounds. The elevated right-sided pressures cause jugular venous distension that worsens during inspiration, and is termed Kussmaul’s sign. Pleural effusions may diminish breath sounds at the bases. Hepatosplenomegaly or ascites may be present on abdominal exam, and peripheral edema is often found. The physical exam is not specific enough, however, to establish the diagnosis.
Measurement of peripheral arterial pressure and central venous pressure is a common practice. Unfortunately, it is usually only the arterial blood pressure and quantitative CVP that is used, and little attention is paid to the actual waveforms. This is surprising because the shape and timing of the pressure waves and the changes that occur during the respiratory cycle can provide useful diagnostic information and should not be overlooked.
The peaks and troughs of the CVP waveform represent pressure changes in the right atrium. (Figure 5a.) The a-wave represents right atrial contraction and correlates with the P wave on the ECG. It disappears during atrial fibrillation. The x-descent occurs before the T-wave on ECG, and represents decreasing right atrial pressure; it is caused by two different processes. First, atrial diastole expands the blood volume returning from the IVC and SVC.
Figure 5a. Normal right atrial pressure waveform.
The second is a movement of the right ventricle, which descends during systole and reduces pressure on the right atria. Within the x-descent, a c-wave can often be seen that is caused by the tricuspid valve being closed during systole and being forced back into the atria. It correlates with the end of the QRS complex. Blood fills the right atrium against a closed tricuspid valve, and a v-wave develops from the accumulation of returning blood. A prominent v-wave can often signify tricuspid insufficiency. The y-descent is the pressure decrease in the right atria initiated by the opening of the tricuspid valve in early ventricular diastole and represents the blood volume moving from the atria to the ventricle. It occurs before the P wave on the ECG.
The CVP waveform in constrictive pericarditis has a distinct pattern that can be explained by our understanding of the underlying hemodynamics. (Figure 5b.) Following the v-wave, an exaggerated early ventricular filling during diastole results in a steep y-descent. Atrial systole is seen as the a-wave. The atrial contents are transported into the ventricles, and the atrial volume is reduced. At that point, constriction of the two atria transiently lessens, resulting in a steep x-descent. The combination of a steep x- and y-descent causes the atrial pressure waveform to resemble the letter W.
Figure 5b. Right atrial pressure waveform in constrictive pericarditis.
2-D echocardiography can be useful in evaluating constrictive pericarditis. A septal bounce can be seen when diastolic filling abruptly stops. 2-D echocardiography can also be used to assess dilation of the IVC and the left-right movement of the interventricular septum, demonstrating preferential filling of the right ventricle during inspiration and left ventricular filling during expiration.
Even more useful in evaluating hemodynamics is pulsed wave Doppler, which can be used to assess the diastolic flow patterns and how it varies with respiration. This provides significant evidence of constrictive physiology. Pulse wave Doppler ultrasound of the flow velocity across the mitral valve is shown in Figure 6. The early diastolic filling velocity is denoted by the E wave, and the atrial systole is seen as the A. The flow is reduced during inspiration. A drop by 33% in the E peak velocity is highly suggestive of constrictive pericarditis. Opposite changes are seen during expiration. (Figure 7.)
Figure 6. Pulsed wave Doppler of mitral valve (simulated).
Figure 7. Respiratory changes of the mitral valve velocity in constrictive pericarditis.
Right and left heart catheterization allows for direct atrial and ventricular pressure measurements. This assists in confirming the diagnosis of constrictive pericarditis and excluding other diagnoses.
This patient’s systems and imaging studies were very suggestive of constrictive pericarditis. He had an echocardiogram that demonstrated constrictive physiology. He ultimately went to the cardiac catheterization lab for a right and left heart catheterization and coronary angiography to confirm the diagnosis and preoperative planning. The treatment for constrictive pericarditis is pericardiectomy, which the patient is still considering. More than 90 percent of patients will have improved symptoms following the procedure.