In normal canine heart, without any septal defects or any other congenital defect in heart, there will be equal output from the right and left ventricles. Blood leaves the right ventricle will circulate through the lungs, then return to the left heart to be ejected to the body.  In this event, the systemic blood flow (Qs) is equal to the pulmonary blood flow (Qp). Therefore, the Qp:Qs ratio is 1:1. In dogs with patent ductus arteriosus, blood passes from the aorta to the pulmonary artery. Thus, the left atrium, left ventricle and pulmonary artery realize a volume overload, but the right atrium and right ventricle do not. The magnitude of a left-to-right shunt can be expressed in terms of the ratio of the volume of pulmonary flow (Qp) and systemic flow (Qs). In normal dogs this ratio is one because, in normal dogs the volume of blood that is pumped to the lungs (Qp) is equal to the volume of blood that is pumped to the body (Qs). In dogs with left-to-right shunts, the Qp–Qs ratio is greater than one. In general, if Qp–Qs ratio is 1.5 or less it is considered a small shunt; a Qp–Qs ratio of 1.5 to 2.0 is considered a moderate shunt; and a Qp–Qs ratio of more than 2.0 is considered a large shunt.

Both in human patients (Sabry et al., 1995) and in experimental canine models (Valdes-Cruz et al., 1983; Valdes-Cruz et al., 1984; Meijboom et al., 1983) the assessment of Qp/Qs using Doppler echocardiography has been validated. Serres et al., 2009 assessed Qp/Qs by the Doppler echocardiographic method in healthy dogs and he reported Qp/Qs offers an attractive approach for the assessment of ICS severity in dogs, because of its non-invasive aspect. However, Serres et al., 2009 opined, for clinical relevance, longitudinal studies has to be conducted in dogs. With this background the study was designed to determine Qp/Qs by Doppler echocardiography in Dilated cardiomyopathy (DCM), Mitral valve disease (MVD) and Patent ductus arteriosus (PDA) affected dogs.

Materials and Methods

Dogs presented to the cardiology service of the Veterinary Teaching Hospital, Veterinary College Bangalore eligible for entry into the study. Dilated cardiomyopathy (37 cases), Mitral valve disease (26 cases) and Patent ductus arteriosus (8 cases) were diagnosed by Doppler echocardiography and these affected dogs were subjected to following assessment.

Doppler Assessment of Left Ventricular Systolic Function

Aortic Outflow

In left apical five chamber view Aortic outflow was recorded (Fig. 1) and following measurement were carried out-

1. Peak velocity of aortic flow
2. Velocity time integral (VTI) – The aortic outflow spectrum was traced, and the area under its curve determined.
3. Ejection time (ET) – the duration of the aortic outflow spectrum (Boon, 2011).

Pulmonic Outflow

In the right cranial short axis views, optimizing the pulmonary trunk Pulmonic outflow was recorded (Fig. 2). The following measurement were carried out-

1. Peak velocity of pulmonic outflow
2. Velocity time integral (VTI) – The pulmonic outflow spectrum was traced, and the area under its curve determined.
3. Ejection time (ET) – the duration of the pulmonic outflow spectrum (Boon, 2011).

Pulmonary to Systemic Flow Ratio (Qp/Qs)

Qp (Pulmonary flow ml) = (3.14× (mpa/2)²×VTIpul

Qs (Systemic flow ml) = (3.14× (Ao/2)²×VTIsys (Serres et al., 2009; Boon, 2011)

Fig. 1: Pulsed wave Doppler sample volume placed within the aorta, just beyond the aortic valves, to record aortic flow profiles in a dog

Fig. 2: Pulsed wave Doppler sample volume is placed just beyond the pulmonic valves to record pulmonic outflow profile in a dog

Statistical Analysis                                                                                     

Data were recorded as percent, Mean ± SE.  The data obtained were subjected to statistical analysis using SPSS 17 software.  Data between DCM, MVD and PDA were analysed by one-way analysis of variance.

Results and Discussion

The assessment of pulmonary to systemic flow ratio (Qp/Qs) in DCM and MVD affected dog were represented in Table 1. The assessment of Qp/Qs in PDA affected dog were represented in Table 2. Pulmonary to systemic flow ratio in DCM, MVD and PDA affected dogs were represented in Table 3.

Table 1: Assessment of Pulmonary to systemic flow ratio (Qp/Qs) in cardiac disease in dogs

Results are in Mean ± SE; **: Significant (P≤0.01);*: Significant (P≤0.05); + significant (P≤0.10); ^ns: Non-significant

Table 2: Assessment of Pulmonary to systemic flow ratio (Qp/Qs) in PDA (N=8)

Results are in Mean ± SE

Table 3: Pulmonary to systemic flow ratio (Qp/Qs) in DCM, MVD and PDA affected dogs

The mean Qp and Qs value in DCM affected dog were 34.54±10.77 and 20.82±3.6 respectively. The mean Qp and Qs value in MVD affected dog were 13.44±2.74 and 18.63±4.08 respectively.  The mean values of Qp/Qs ratio in DCM and MVD were 1.16±0.21 and 0.72±0.31 respectively. There was no significant difference between these groups. The normal range of Qp/Qs flow ratio was 0.71-1.29 (Serres et al., 2009).   In the present study Qp/Qs ratio was normal in DCM and MVD affected dogs, which is in agreement with the results of earlier workers (Serres et al., 2009). In the case of left to right shunting associated with intracardiac shunts, an increase in Qp may be observed due to pulmonary over circulation, and thus leading to an increase in Qp/Qs ratio. The mean values of Qp, Qs and Qp/Qs ratio was 25.62±4.47, 14.99±5.02 and 1.2±0.16 respectively in PDA affected dogs. Increase in Qp may be observed due to pulmonary over circulation, these leading to an increase in Qp/Qs ratio. Left to right shunting associated with intracardiac shunts in PDA leads to above mentioned condition. These findings are in agreement with earlier observations of Serres et al. (2009).

Conclusion

The combination of pulmonary to systemic flow ratio (Qp/Qs) with Doppler parameters, offers a striking approach for the assessment of intra cardiac shunt severity in dogs.  Further, the present method is rapid, easy and non-invasive and aids in early diagnosis.

References

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