Definition = a condition in which the pressure in the pericardial space is increased, resulting in hemodynamic abnormalities that reflect compression of the chambers of the heart. Hemodynamic abnormalities due to compression of the heart constitute a spectrum.
Compromise of the circulation represents an advanced degree. Any syndrome of hemodynamic abnormalities caused by fluid under increased pressure in the pericardial space.
Pathophysiology
- hemodynamic effects of pericardial disease result entirely from interference with cardiac filling
- low CO with high CVP = pericardial, myocardial, valvular, pulmonary vascular disease
- understanding the pathophysiology of disordered cardiac filling helps distinguish between cardiac tamponade , constrictive pericarditis , and effusive-constrictive pericarditis
- pericardial space pressure normally equal to intrapleural pressure, with the mean value close to atmospheric pressure
- with inspiration, pleural pressure becomes more negative, with increased Venous Return, and increased filling of RA. This increased filling means higher transmural pressures but we record a fall in right-sided pressures because the reference point ( atmospheric ) has not changed, but the more negative pleural pressures are transmitted through the pericardium to the heart. Therefore RAP normally falls with inspiration despite increased filling.
- Ventricular systole - AV valve closed
- Increased Venous Return - increasing RAP = V wave
- Ventricular diastole - ventricular pressure drops below RAP and thus the
AV valve
opens
- passive flow from atria to ventricles occurs in early diastole = Y descent
- ventricle fills - Atrial to Ventricular pressure gradient narrows, and flow stops in mid-diastole
- atrial systole or contraction results in a rapid rise in RAP with additional flow from the atria to ventricles = A wave
- AV valve closes - flow stops
- isovolumic atrial relaxation = X descent
- Pericardial pressure is distributed equally among all chambers since pericardial fluid is free flowing. This reduces the gradients between chambers throughout diastole. This is inconsequential in small effusions, but becomes hemodynamically significant in large effusions in which a greater pressure in the pericardium is transmitted to all four cardiac chambers resulting in "equalization of central pressures". The reduction of the pressure gradient between the atria and the ventricles when the AV valves open mean that there is less transfer of blood from the atria to the ventricles. This is seen as a loss of the y-descent of the CVP or PCWP waveform tracings.
- In contrast, the thickened pericardium in constrictive pericarditis does not restrict chamber enlargement at low volumes and therefore does not impair early diastolic filling but at higher volumes the limiting constraint is reached and filling is limited and the pressures in all chambers will become equal. Filling is preserved in early diastole but compromised in late diastole.
- The effective pressure ( Ptm or transmural pressure) that distends the cardiac chambers is the difference between intracardiac and intrapericardial pressures. Normally, there is 10 - 20 ml fluid in the pericardial space ( minimal ).Pericardial restraint is recognized as an important function of the normal pericardium. Pericardial pressures rise abruptly when the volume rises above 200 cc.
- Ppericardium normally lower than Pright atrium allowing distension of RA
Pmean systemic > JVP > Pra > P peri
When Pperi > 6 cmH2O, then these pressures become more equal and ventricular filling is compromised.
If Pperi > Pchamber then cardiac filling cannot occur.
Pericardial pressure is an external pressure which pushes on the cardiac chambers. Relative to atmosphere, a given chamber volume will generate a greater intracavitary pressure if it is squeezed externally. Ptm is the actual distending pressure. Therefore, the Pmeasured does not reflect volume ( preload ) and thus in tamponade the preload will be on the ascending portion of the Starling curve.
An effusion is equally distributed and thus equalize pressures across chambers. Therefore no gradient for flow exists except during atrial contraction. In early diastole filling does not occur = absence of the y descent.
- Get compensatory rise in CVP by venoconstriction and increased vascular volume. Stroke Volume is maintained by increase in Ejection Fraction. CO maintained by increase in HR. MAP maintained by vasoconstriction- until a late decompensation occurs. The reduced size of the LV lowers myocardial wall tension and O2 demand is protective.
Diagnosis ( Tamponade )
- elevated diastolic pressures
- equal end-diastolic pressures in RV or LV ( or PCWP )
- absence of ventricular filling early in diastole
- absence of Y descent in atrial tracings
Diagnosis ( Constrictive Pericarditis )
- elevated diastolic pressures
- equalization of diastolic pressures in the RV and LV
- completion of diastolic filling in early diastole ( dip and plateau in ventricular trace )
- rapid x and y descents
- Kussmal's
Clinical Occurrence
- penetrating trauma
- -aortic dissection
- perforation from cardiac cath, pacer, PTCA, central line
- post CABG
- viral pericarditis
- neoplasm
- radiotherapy
- uremia
- CTD
- bacterial, TB
- Dressler/ myocardial rupture
Clinical
- dyspnea
- fullness in abdomen due to liver and GI congestion
- ascites
- substernal pleuritic chest pain, relief with sitting
- muffled HS
- absent S3 ( limitation of early diastolic rapid filling phases
- absent S4 ( atrium has decreased effective pressure)
- pericardial friction rub
- compensatory venoconstriction may make detection of JVD difficult
- Beck's triad = muffled HS, JVD, hypotension
- SV low because of inadequate EDV
- PP usually < 40
- pulsus is result of fall in LV SV
- increase VR in inspiration
- distension of RV
- septal shift to L
- compromised filling of LV
- all that is required for pulsus to develop is an increase in VR with inspiration to a heart that is limited in its ability to expand
- tachycardia
- atrial dysrhythmias
Waveforms
- Y descent ( early diastolic fall in pressure ) is diminished or absent
- distinguishes from constrictive pericarditis or right-sided CHF, where the Y descent is typically the most prominent part of the waveform
Kussmal's sign
- abdominal pressure rises with inspiration so that the driving pressure to translocate blood into the thorax during inspiration is negative pleural pressure plus positive intraabdominal pressure
- ie; the abdominal drivng pressure
- requires steep compliance curve of right side so that the rise in RAP with volume load is greater than the drop in ITP
- also requires "full tank " to translocate enough volume, thus elevated CVP is necessary to generate Kussmal's
- cardiomyopathy, PE, RV infarct
- does not occur in uncomplicated tamponade
Paradoxic Pulse
- an exaggerated fall in systemic arterial pressure with inspiration > 15 mmHg
- waxing and waning of LV stroke volume with inspiration
- waxing and waning of VR with respiration
- RV and LV filling wax and wane out of phase with each other
- inspiration leads to increased RV filling and decreased LV filling
- total volume of the heart is relatively fixed when the heart is surrounded by a tense pericardial effusion, increase in RV volume with inspiration occurs at the expense of LV volume with shift of ventricular septum to the left, reduction of LV volume
- increase shift of septum in tamponade because RV can't expand into the pericardial space
- lungs outside the constriction, thus with inspiration blood tends to pool in the lungs
- occurs in tamponade, COPD, asthma, PE, RV infarct, shock, constrictive pericarditis
Radiologic
- increased cardiomediastinal silhouette, water bottle sign
- clear lung fields ( absence of congestion )
EKG
- low voltage
- electrical alternans
- ST - T changes due to pericarditis
ECHO
- pericardial effusion
- swinging of the heart
- exaggerated changes with respiration
- volume of R and L ventricles
- movement of the ventricular septum
- velocity of diastolic flows through MV and TV
- absent variability in SVC and hepatic vein flows with resp
- right atrial collapse when Pperi > Pra
- collapse indicates that pericardial pressure exceeds intracavitary pressure at
- least briefly at some point in the cardiac cycle
- RV collapse
Localized Cardiac Tamponade
- RA and RV - resembles SVC obstruction
- LA - pulmonary edema
- unusual clinical and hemodynamic features when it is associated with localized compression of the heart, CHF, volume depletion, or visceral constrictive pericarditis
Effusive-Constrictive Pericarditis
Therapy
- moderate = CVP > 10 or SBP < 100
- pericardiocentesis or window
- fluids
- vasoactive drugs
- afterload reduction may reduce cardiac size and lessen compression
Patrick Melanson, MD, FRCPC