Intracardiac shunts


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Intracardiac shunts

  1. 1. Dr. Fuad Farooq Resident Cardiology Aga Khan University Hospital
  2. 2.  Normal circulation  Left to right shunting of blood as in ASD,VSD and PDA  Unoxygenated blood can be shunted from the right heart to the left heart - Eisenmenger syndrome  Intracardiac shunts can be either congenital or acquired e.g., VSD as a complication of myocardial infarction
  3. 3.  Detection, localization and quantification of intracardiac shunts are an integral part of the hemodynamic evaluation in these patients
  4. 4.  Intracardiac shunting of blood results when there is an opening between the right and left heart chambers and a pressure difference between the connected chambers  Pressures on the left side of the heart are generally higher than on the right side so most shunts are predominantly left to right although right to left and bidirectional shunts are seen (predominantly in Eisenmenger syndrome)
  5. 5.  Many techniques are available for the detection intracardiac shunts • Indicator dilution method – Injecting indocyanine green into a right sided heart chambers and then monitoring its appearance in the systemic circulation • Contrast angiography – Contrast dye is injected into high pressure chamber of suspected shunt • Oximetry run – Most frequently used measurement of the oxygen saturations in various locations in the venous system and the right heart
  6. 6.  Basic technique for detecting and quantifying left to right shunts  Oxygen content or percent saturation is measured in blood samples drawn sequentially from the pulmonary artery, right ventricle, right atrium, superior vena cava and inferior vena cava  A left to right shunt may be detected and localized if a significant step-up in blood oxygen saturation is found in one of the right heart chambers
  7. 7.  Samples need to be acquired with the patient breathing room air or a gas mixture containing no more than a maximum of 30% oxygen  Saturation data may be inaccurate in patients breathing more than 30% oxygen, as a significant amount of oxygen may be present in dissolved form in the pulmonary venous sample  Dissolved oxygen is not factored into calculations when saturations are used and thus pulmonary flow will be overestimated and the amount of shunt exaggerated Heart 2001;85:113–120.
  8. 8. The simplest way to screen for a left to right shunt is to sample SVC and pulmonary artery blood and measure the difference in O2 saturation if >=8%, a left to right shunt may be present at atrial, ventricular or great vessel level, and a full oximetry run should be done
  9. 9.  Samples are obtain (2-mL) from each of the following locations with the end hole catheter
  10. 10.  To ensure the results are as accurate as possible, the samples must be collected as close in time as good technique permits  Blood samples should not be withdrawn into the syringe too rapidly, “rapid aspiration increased oxygen saturations”  Complete mixing of blood is assumed in all chambers Matta et al. Anesthesiology 1997;86:806–808.
  11. 11.  Oximetry method of quantifying shunts loses accuracy when determining small shunts or in the presence of high cardiac output (which decreases AVO2 difference)  The magnitude of the step-up varies with the oxygen carrying capacity of blood  Relationship between the magnitude of step-up and the shunt flow is nonlinear and with increasing left to right shunting, a given change in shunt flow produces less of a change in the saturation step-up
  12. 12.  Saturation step-ups are increased if hemoglobin concentration is low or cardiac output is low
  13. 13. Hillis et al. found that the difference between RA and PA saturations in 980 patients without intracardiac shunts was 2.3% ± 1.7%. In this same population,the difference between SVC and RA saturations was 3.9% ± 2.4% Using threshold values of 8.7% and 5.7% respectively, between SVC to RA and RA to PA as “cut-offs” to identify patients with intracardiac shunts had excellent sensitivity and specificity Am J Cardiol 1986;58:129–132
  14. 14. Level of shunt Difference in O2 saturation Differential diagnosis Atrial (SVC/IVC to RA) >7% ASD; PAPVD; Ruptured sinus of Valsalva; VSD with TR; Coronary to RA fistula Ventricular (RA to RV) >5% VSD; PDA with PR; Primum ASD; coronary to RV fistula Great Vessel (RV to PA) >5% PDA; AP window; Aberrant coronary artery origin Any level (SVC to PA) >7% All the above
  15. 15.  Generally done in two ways 1. The ratio of pulmonary blood flow versus the systemic blood flow can be calculated (QP/QS) 2. Calculation of actual flow of the shunt by difference between the pulmonary blood flow and the systemic blood flow  These two are equal in a normal heart
  16. 16. Quantification of shunt size using Qp/Qs is not affected by hemoglobin concentration and the relationship between Qp/Qs and shunt flow is linear
  17. 17.  If a PV has not been entered, systemic arterial oxygen content may be used if >95%
  18. 18.  If systemic oxygen saturation is <95% then, • Must determine whether a right to left intracardiac shunt is present • If right to left shunt is present then an assumed value for pulmonary venous oxygen content of 98% oxygen capacity should be used • If no right to left intracardiac shunt is found, then the observed systemic arterial oxygen saturation should be used to calculate pulmonary blood flow
  19. 19. Oxygen consumption can measured by using the metabolic rate meter Mixed venous oxygen content must be measured in the chamber immediately proximal to the shunt
  20. 20. Location of shunt as determined by site of O2 step-up Mixed venous sample to use in calculating systemic blood flow 1. Pulmonary artery (e.g., patent ductus arteriosus) Right ventricle 2. Right ventricle (e.g., ventricular septal defect) Right atrium 3. Right atrium (e.g., atrial septal defect) 3 SVC + 1 IVC 4
  21. 21. These equations are simplified as Since pulmonary veins are rarely entered during a cardiac cath, a pulmonary catheter wedge sample or LA sample (if the LA is entered via an ASD) can be used in its place Alternatively, arterial saturation can be substituted or an assumed value of 98% may be used
  22. 22.  Qp/Qs can be a very useful tool in making decisions about the need for repair of a shunt • Qp/Qs of 1–1.5 – observation is generally recommended. • Qp/Qs ratio of 1.5–2.0 – significant enough that closure (either surgically or percutaneously) should be considered if the risk of the procedure is low • Qp/Qs ratio of greater than 2 – closure (either surgically or percutaneously) should be undertaken unless there are specific contraindications
  23. 23. If there is no evidence of an associated right to left shunt, the left-to-right shunt is calculated by
  24. 24.  Primary indication for the use of techniques to detect and localize right to left intracardiac shunts is the presence of cyanosis, or more commonly, arterial hypoxemia  Right to left shunting is unusual except in the case of Eisenmenger syndrome  Qp/Qs will be less than 1
  25. 25.  In right to left shunting, the effective pulmonary flow is reduced by the amount of the shunt Flow through the + Flow through the shunt = Flow through the pulmonary valve aortic valve
  26. 26. 1. Angiography: May demonstrate Right to Left intracardiac shunts Important in detecting Right to Left shunting owing to a pulmonary AVF Although angiography may localize Right to Left shunts, it does not permit quantification
  27. 27. 2. Oximetry : The site of Right to Left shunts may be localized if blood samples can be obtained from a pulmonary vein, LA, LV and aorta The pulmonary venous blood of patients with arterial hypoxemia caused by an intracardiac Right to Left shunt is fully saturated with oxygen Site of a Right to Left shunt may be localized by noting which left heart chamber is first to show desaturation (i.e., a step-down in oxygen concentration)
  28. 28. e.g., If LA blood oxygen saturation is normal but desaturation is present in the LV and in the systemic circulation, the Right to Left shunt is across a VSD
  29. 29.  The only disadvantage of this technique is that a pulmonary vein and the left atrium must be entered • This is not as easy in adults as it is in infants, in whom the left atrium may be entered routinely by way of the foramen ovale
  30. 30.  Simplified approach to the calculation of simultaneous right-to-left and left-to- right (also known as bidirectional) shunts makes use of a hypothetic quantity known as the effective blood flow, the flow that would exist in the absence of any left-to-right or right-to-left shunting
  31. 31. Oxygen content = hemoglobin × 1.36 × percent saturation The approximate left-to-right shunt then equals Qp - Qeff, and the approximate right-to-left shunt equals Qs - Qeff
  32. 32.  Pulmonary circulation is characterized by high flow, low pressure and low resistance system  Normal pulmonary systolic pressures are 18-25 mm Hg, end diastolic pressure ranges from 6-10 mm Hg and mean pulmonary arterial pressures of 10-16 mm Hg  Pulmonary hypertension is define as mean pulmonary artery pressure (MPAP) >25 mm Hg at rest or > 30mmHg on exercise or systolic pulmonary artery pressure >30 mm Hg  Pulmonary artery pressure increase in response to increase on LA pressures, pulmonary vascular resistance and cardiac output
  33. 33.  The pulmonary vasculature is a dynamic system and is subject to many mechanical, neural and biochemical influences  Pulmonary vascular resistance provides general information about the pulmonary circulation but this must be interpreted in the context of the clinical situation and other hemodynamic data obtained during cardiac catheterization
  34. 34.  Expressed in Woods unit (1WU=1mm Hg/L = 80 dynes/cm3 )  Normal value is < 3 WU or 150 – 250 dynes/sec/cm3  PVR is one sixth SVR
  35. 35.  Factors increases PVR • Hypoxia • Hypercapnia • Increased sympathetic tone • Polycythemia • local release of serotonin • Mechanical obstruction by multiple pulmonary emboli • Precapillary pulmonary edema • Lung compression (pleural effusion, increased intrathoracic pressure via respirator)
  36. 36.  Factors that decreases PVR: • Oxygen • Adenosine • Isoproterenol • Inhaled nitric oxide • Prostacyclin infusions • High doses of calcium channel blockers
  37. 37.  Pulmonary vasoreactivity can be checked with the help of • 100% oxygen • Adenosine • Epoprostenol • Inhaled nitric oxide
  38. 38.  Positive response is define as: • 20% fall in pulmonary artery pressure and PVR or decrease in mean pulmonary artery pressure of 10 mm Hg to an absolute value of less than 40 mm Hg without in decrease in cardiac output  These are the patient who are most benefited from corrective procedure and calcium channels blockers
  39. 39.  The ratio between pulmonary vascular resistance and systemic vascular resistance (resistance ratio) can be used as a criterion for operability in dealing with congenital heart disease • Normally, this ratio is <0.25 • Values of 0.25 to 0.50 indicate moderate pulmonary vascular disease • Values greater than 0.75 indicate severe pulmonary vascular disease • When the PVR/SVR resistance ratio equals 1.0 or more, surgical correction of the congenital defect is considered contraindicated because of the severity of the pulmonary vascular disease
  40. 40. Q 1. What is the level of shunt? Q 2. What is the direction of shunt? Q 3. What is diagnosis? Q 4. What is Qp/Qs
  41. 41. Q 1.What is the level of shunt? Q 2.What is the direction of shunt? Q 3.What is diagnosis? Q 4.What is Qp/Qs?
  42. 42. Q 1. What is the level of shunt? Q 2. What is the direction of shunt? Q 3. What is diagnosis? Q 4. What is Qp/Qs
  43. 43. Q 1.What is the level of shunt? Q 2.What is the direction of shunt? Q 3.What is diagnosis? Q 4.What is Qp/Qs
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