pathophysiology of Left to right shunt

this is a presentation, giving idea about pathophysiology of left to right shunt in congenital heart disease.

1. PATHOPHYSIOLOGY OF LEFT TO RIGHT SHUNT Dr. Dhaval A Bhimani

2. Normal hemodynamics

3. Atrial septal defect

4. Atrial septal defect

5. Key points LA is not enlarged Because of increased pulmonary venous return to LA does not stay  goes into RA. Absence of LA enlargement is one of the helpful X-RAY findings for differentiating ASD from VSD. Prolong depolarisation of RV because of enlargement lead to RBBB. Left to right shunt is silent in ASD. Murmur is because of high flow through normal pulmonary valve  relative stenosis. So, heard more in systole, in pulmonary area, (Upper left Sternal border)

6. Shunt is large  more flow through TV  relative TV stenosis. Wide split S2 ( delayed depolarisation of RV  late closure of PV ) Important:- 1- Infant and small children does not have classical symptom until 3-4 year ?? Because compliance of RV improve slowly so that any significant shunt does not occuruntil that age. 2 - CHF is rare in children even in presence of large shunt?? PA can handle blood flow for longer period without developing CHF because of no direct systemic flow to PA. However, Pulmonary HTN developes by third to fourth decade.

7. Ventricular septal defect

8. Ventricular septal defect

9. Key points Acynotic VSD is L  R shunt, shunt determined  by the size, not the location of the defect and the level of pulmonary vascular resistance (PVR).  small VSD  large resistance to shunt occurs at the defect, and the shunt does not depend on the level of PVR  normally PVR large VSD  Minimal resistance  shunt depends largely on the level of PVR. lower the PVR, the greater the magnitude of the left-to-right shunt. This type of left-to-right shunt is called a  dependent shunt.

10. In VSD, it is the LV that does volume overwork, not the RV. This results in LV enlargement; the RV does not enlarge. WHY ?? Because the shunt of VSD occurs mainly during systole when the RV also contracts, the shunted blood goes directly to the PA rather than remaining in the RV cavity. VSD & PDA both has LA,LV enlargement.

11. Small VSD Small flow in shunt (only half arrow)  minimal PVR & other changes. Murmur is due to shunt itself (regurgitant systolic) Moderate VSD One arrow shunt  significant changes, LVH RV is not significant volume pressure load, so no RVH. Due to pressure flow across MV leads to relative stenosis of MV  MDM murmur, best at apex. PA is mild elevated  p2 may be loud.

12. Large VSD Relatively more chamber enlargement due to more flow across shunt Direct pressure to RV  RVH. Bi-ventricular enalargement in bith ECG & X-ray. Along with LA enlargement. A large VSD usually results in CHF in early infancy

13. What if left, Untreated ?? Irreversible changes take place in the pulmonary arterioles, producing pulmonary vascular obstructive disease (or Eisenmenger’s syndrome). May take years to develop this canges . PVR  L R Shunt. Eventually lead to decrease in LA ,LV size. Only RVH remains. Cynosis is present. S2 is Loud due to PAH.

14. Patent Ductus Arteriosus(PDA)

15. Patent Ductus Arteriosus(PDA)

16. Key points Hemodynamics of PDA are similar to those of VSD. The magnitude of the left-to-right shunt is determined by the  resistance  offered by the ductus (i.e., diameter, length, and tortuosity) when the ductus is small and level of PVR is large ( i.e.,dependent shunt). Similar Of VSD.

17. Hemodynamic consequences of PDA are similar to those of VSD. LA ,LV enlarge same as VSD, Except here Aorta upto level of PDA is enlarged. Continuous murmur Small Shunt- No significant changes. Moderate shunt- LA, LV & PA enlarge, ECG - s/o LVH. In addition, there may be an apical diastolic flow rumble as a result of relative stenosis of the mitral valve. The P2 slightly increases in intensity if it can be separated from the loud heart murmur.

18. Large Shunt:- marked cardiomegaly and increased pulmonary vascular markings are present LVH, & occasionally LAH in ECG. The free transmission of the aortic pressure to the PA produces pulmonary hypertension and RV hypertension, with resulting RVH on the ECG. ECG shows BVH and LAH, as in a large VSD. The continuous murmur is present, with an apical diastolic rumble owing to relative mitral stenosis. The P2 is accentuated in intensity due to pulmonary hypertension.

19. What if left, Untreated ?? Irreversible changes take place in the pulmonary arterioles, producing pulmonary vascular obstructive disease (or Eisenmenger’s syndrome). As in VSD, Eventually lead to decrease in LA ,LV size. Only RVH remains. Cynosis is present , but only in lower half of body. ECG- RVH, NO LVH. No continuous murmur, only S2 is single & Loud due to PAH.

20. Endocardial Cushion Defect

21. Introduction During fetal life, the endocardial cushion tissue contributes to the closure of both the lower part of the atrial septum (i.e., ostium primum) and the upper part of the ventricular septum in addition to the formation of the mitral and tricuspid valves. The failure of normal development of this tissue may be either complete or partial. A simple way of understanding the complete form of endocardial cushion defect (ECD) is that the tissue in the center of the heart is missing, with resulting VSD, the primum type of ASD, and clefts in the mitral and tricuspid valves. In the partial form of the defect, only an ASD is present in the ostium primum septum (primum type of ASD), often associated with a cleft in the mitral valve.

22. primum-type ASD Hemodynamic abnormalities of primum-type ASD are similar to those of secundum-type ASD, in which the RA and RV are dilated with increased pulmonary blood flow. The cleft mitral valve is usually insignificant from a hemodynamic point of view because blood regurgitated into the LA is immediately shunted to the RA, thereby decompressing the LA. The physical findings are also similar to those of secundum ASD: a widely split and fixed S2, a systolic ejection murmur at the upper left sternal border, and a mid-diastolic rumble of relative tricuspid stenosis at the lower left sternal border. Systolic murmur of mitral regurgitation (MR) is occasionally present.

23. ECG RBBB, mild RVH. One exception, which is important in differentiating between the two types of ASDs, is the presence of a “superior” QRS axis or left anterior hemiblock (with the QRS axis in the range of −20 to −150 degrees) in primum-type ASD. It occurs as a result of the primary abnormality in the development of the bundle of His and the bundle branches.

24. complete ECD Hemodynamic changes seen with complete ECD are the sum of the changes seen in ASD and VSD. There is volume overload of the LA and LV as in VSD and partially due to MR. In addition, it has volume overload of the RA and RV as in ASD. The result is biatrial and biventricular enlargement. he magnitude of the left-to-right shunt in complete ECD is determined by the level of PVR (i.e., dependent shunt). 

25. ECG & Clinical findings BVH and occasional biatrial hypertrophy (BAH) “Superior” QRS axis is also characteristic of ECD. Hyperactive precordium Regurgitant systolic murmurs of VSD and MR, Loud and narrowly split S2 (because of PAH), Apical or tricuspid diastolic rumble (or both), and Signs of CHF.  Those who survive infancy may develop pulmonary vascular obstructive disease, as already discussed for large VSD and large PDA

26. DIRECT COMMUNICATION BETWEEN THE LV AND RA This may occur as part of ECD (or as an isolated defect unrelated to ECD). The direction of the shunt is from the high-pressure LV to the low-pressure RA. The magnitude of the shunt is determined by the  size  of the defect, regardless of the state of PVR; blood shunted to the RA must go forward through the lungs even if the PVR is high. This type of shunt, which is independent of the status of PVR, is called an  obligatory shunt.

27. When an LV-RA shunt is present as part of complete ECD, CHF may occur within a few weeks, which is earlier than in the usual VSD. The enlarged chambers are identical to those of the complete form of ECD. Therefore, the chest radiographs and ECG findings are similar to those seen in complete ECD.  Physical findings also resemble those of complete ECD, although the holosystolic murmur (resulting from the LV-RA shunt) may be more prominent at the mid-right sternal border.

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