Quantification of right to left shunt through pulmonary arteriovenous malformations using 99Tcm albumin microspheres

Exercise capacity reflects airflow limitation rather than hypoxaemia in patients with pulmonary arteriovenous malformations

BACKGROUND

Pulmonary arteriovenous malformations (PAVMs) generate a right-to-left shunt. Impaired gas exchange results in hypoxaemia and impaired CO2 clearance. Most patients compensate effectively but some are dyspneic, and these are rarely the most hypoxaemic.

AIM

To test degrees of concurrent pathology influencing exercise capacity.

DESIGN

Replicate, sequential single centre, prospective studies.

METHODS

Cardiopulmonary exercise tests (CPETs) were performed in 26 patients with PAVMs, including individuals with and without known airflow obstruction. To replicate, relationships were tested prospectively in an independent cohort where self-reported exercise capacity evaluated by the Veterans Specific Activity Questionnaire (VSAQ) was used to calculate metabolic equivalents (METs) at peak exercise (n = 71). Additional measurements included oxygen saturation (SpO2), forced expiratory volume in 1 s (FEV1), vital capacity (VC), fractional exhaled nitric oxide (FeNO), haemoglobin and iron indices.

RESULTS

By CPET, the peak work rate was only minimally associated with low SpO2 or low arterial oxygen content (calculated as CaO2=1.34 × SpO2 × haemoglobin), but was reduced in patients with low FEV1 or VC. Supranormal work rates were seen in patients with severe right-to-left shunting and SpO2 < 90%, but only if FEV1 was >80% predicted. VSAQ-calculated METS also demonstrated little relationship with SpO2, and in crude and CaO2-adjusted regression, were lower in patients with lower FEV1 or VC. Bronchodilation increased airflow even where spirometry was in the normal range: exhaled nitric oxide measurements were normal in 80% of cases, and unrelated to any PAVM-specific variable.

CONCLUSIONS

Exercise capacity is reduced by relatively mild airflow limitation (obstructive or restrictive) in the setting of PAVMs.

Veterans Specific Activity Questionnaire (VSAQ): a new and efficient method of assessing exercise capacity in patients with pulmonary arteriovenous malformations

Introduction

Assessment of performance status is an important component of clinical management of patients with pulmonary arteriovenous malformations (PAVMs). Usual methods are time-consuming and insensitive to variations within normal or supranormal exercise capacity.

Methods

The Veterans Specific Activity Questionnaire (VSAQ) was modified to facilitate completion by patients independently. Patient-reported activity limitations were converted to the Medical Research Council (MRC) Dyspnoea Scale, New York Heart Association (NYHA) classification and metabolic equivalents (METs) in which 1 MET equals the consumption of 3.5 mL O₂ per kilogram of body weight per minute.

Results

The study population consisted of 71 patients with PAVMs aged 20-85 (median 52) years. Oxygen saturation (SaO₂) was 80%-99.5 % (median 96%), and haemoglobin was 73-169 g/L in women and 123-197 g/L in men (p<0.0001). Arterial oxygen content (CaO₂) (1.34 × [haemoglobin × SaO₂]/100) was maintained unless iron deficiency was present. Most patients (49/71, 69%) did not need to stop until activities more energetic than walking briskly at 4 mph were achieved (6.4 km per hour, VSAQ >5, MRC Dyspnoea Scale 1 or 2, NYHA class I). SaO₂ was inversely associated with the MRC Dyspnoea Scale and NYHA class, but not the VSAQ. Raw VSAQ scores captured a marked difference between men and women. METs were also higher in men at 3.97-15.55 (median 8.84) kcal/kg/min, compared with 1.33-14.4 (median 8.25) kcal/kg/min (p=0.0039). There was only a modest association between METs and SaO₂ (p=0.044), but a stronger association between METs and haemoglobin (p =0.001). In crude and sex-adjusted regression, the CaO₂ was more strongly associated with METs than either SaO₂ or haemoglobin in isolation.

Conclusion

The VSAQ, capturing patient-reported outcome measures, is an efficient and quantifiable measure of exercise capacity that can be readily employed in clinical services particularly where patients have normal to high exercise tolerance. In the PAVM population, exercise capacity reflects haemoglobin and CaO₂ more than SaO₂, even where SaO₂ measurements are low.

Hemoglobin Is a Vital Determinant of Arterial Oxygen Content in Hypoxemic Patients with Pulmonary Arteriovenous Malformations

RATIONALE

Pa_O2 and Sa_O2 are commonly measured in respiratory practice, but arterial oxygen content (Ca_O2) refers to the volume of oxygen delivered to the tissues per unit blood volume. Ca_O2 is calculated from Sa_O2 and the hemoglobin concentration in blood, recognizing that each gram of hemoglobin can transport approximately 1.34 ml of oxygen when fully saturated.

OBJECTIVES

To prospectively evaluate serial changes in Ca_O2 in humans, incorporating and excluding dynamic changes to oxygenation and hemoglobin parameters that may occur during life.

METHODS

A cohort of 497 consecutive patients at risk of both hypoxemia and anemia were recruited. The patients had radiologically proven pulmonary arteriovenous malformations (PAVMs), which result in hypoxemia due to right-to-left shunting, and concurrent hereditary hemorrhagic telangiectasia, which placed them at risk of iron deficiency anemia due to recurrent hemorrhagic iron losses. Presentation Sa_O2 (breathing room air, by pulse oximetry), hemoglobin, red cell and iron indices were measured, and Ca_O2 calculated as Sa_O2 × hemoglobin × 1.34 ml/g. Serial measurements were evaluated in 100 cases spanning up to 32.1 (median, 10.5) years.

RESULTS

Presentation Ca_O2 ranged from 7.6 to 27.5 (median, 17.6) ml/dl. Ca_O2 did not change appreciably across the Sa_O2 quartiles. In contrast, hemoglobin ranged from 5.9 to 21.8 g/dl (median, 14.1 g/dl), with a linear increase in Ca_O2 across hemoglobin quartiles. After PAVM embolization and an immediate increase in Sa_O2, hemoglobin fell and Ca_O2 was unchanged 1.6-12 (median, 4) months later. When hemoglobin fell because of iron deficiency, there was no change in Sa_O2. Similarly, when hemoglobin rose after iron treatment, there was no change in Sa_O2, and the expected Ca_O2 increment was observed. These relationships were not evident during pregnancy when hemoglobin fell, and PAVMs usually deteriorated: in pregnancy Sa_O2 commonly increased, and serial Ca_O2 values (incorporating hemodilution/anemia) more accurately reflected deteriorating PAVM status. An apparent fall in Ca_O2 with age in females was attributable to the development of iron deficiency. There was an unexplained increase in Ca_O2 with age in follow-up of males after embolization.

CONCLUSIONS

Hemoglobin/Ca_O2 should be further incorporated into oxygenation considerations. More attention should be given to modest changes in hemoglobin that substantially modify Ca_O2.

Pulmonary arteriovenous malformation in a neonate: a condition commonly misdiagnosed

Pulmonary arteriovenous malformations (PAVMs) are congenital defects in the form of an anomalous bridging between a pulmonary arterial and venous system that sidesteps the normal pulmonary capillary. This anomaly is usually associated with hereditary hemorrhagic telangiectasia, leftover small group are sporadic cases but may occur as an isolated anomaly or as multiple lesions. Rarely, such abnormalities can be acquired. Few cases are diagnosed in the neonatal period, as it will pass silent without symptoms. Clinical manifestations occur soon after birth as cyanosis, tachypnea, and an abnormal sound as bruit over the AVM; and the most important point is the clinical suspicion of diagnosis in absence of pulmonary parenchymal and cardiac disease that can explain the persistence of cyanosis. We report a successful Amplatzer vascular plug occlusion of isolated multiple left side PAVM in a neonate, which was done on two stages with a 6 months interval, with no complications. Over 2-year follow-up, the patient remained well with no symptoms.

Cardiopulmonary exercise testing demonstrates maintenance of exercise capacity in patients with hypoxemia and pulmonary arteriovenous malformations

BACKGROUND

Patients with pulmonary arteriovenous malformations (PAVMs) are unusual because hypoxemia results from right-to-left shunting and not airway or alveolar disease. Their surprisingly well-preserved exercise capacity is not generally appreciated.

METHODS

To examine why exercise tolerance is preserved, cardiopulmonary exercise tests were performed while breathing room air in 21 patients with radiologically proven PAVMs, including five restudied 3 to 12 months after embolization when their PAVMs had regressed. Where physiologic matching was demonstrable, comparisons were made with 12 healthy control subjects.

RESULTS

The majority of patients achieved their predicted work rate despite a resting arterial oxygen saturation (SaO₂) of 80% to 96%. Peak work rate and oxygen consumption (VO₂) were no lower in patients with more hypoxemia. Despite higher SaO₂ following embolization (median, 96% and 90%; P = .009), patients achieved similar work rates and similar peak VO₂. Strikingly, treated patients reset to virtually identical peak oxygen pulses (ie, VO₂ per heart beat) and in many cases to the same point on the peak oxygen pulse/work rate plot. The 21 patients had increased minute ventilation (VE) for given increases in CO₂ production (VE/VCO₂ slope), but perceived dyspnea was no greater than in the 12 control subjects or in the same patients before compared to after embolization comparison. Overall, work rate and peak VO₂ were associated not with oxygenation parameters but with VE/VCO₂ slope, BMI, and anaerobic threshold.

CONCLUSIONS

Patients with hypoxemia and PAVMs can maintain normal oxygen delivery/VO₂ during peak exercise. Following improvement of SaO₂ by embolization, patients appeared to reset compensatory mechanisms and, as a result, achieved similar peak VO₂ per heart beat and peak work rates.

Arterial oxygen content is precisely maintained by graded erythrocytotic responses in settings of high/normal serum iron levels, and predicts exercise capacity: an observational study of hypoxaemic patients with pulmonary arteriovenous malformations

BACKGROUND

Oxygen, haemoglobin and cardiac output are integrated components of oxygen transport: each gram of haemoglobin transports 1.34 mls of oxygen in the blood. Low arterial partial pressure of oxygen (PaO2), and haemoglobin saturation (SaO2), are the indices used in clinical assessments, and usually result from low inspired oxygen concentrations, or alveolar/airways disease. Our objective was to examine low blood oxygen/haemoglobin relationships in chronically compensated states without concurrent hypoxic pulmonary vasoreactivity.

METHODOLOGY

165 consecutive unselected patients with pulmonary arteriovenous malformations were studied, in 98 cases, pre/post embolisation treatment. 159 (96%) had hereditary haemorrhagic telangiectasia. Arterial oxygen content was calculated by SaO2 x haemoglobin x 1.34/100.

PRINCIPAL FINDINGS

There was wide variation in SaO2 on air (78.5-99, median 95)% but due to secondary erythrocytosis and resultant polycythaemia, SaO2 explained only 0.1% of the variance in arterial oxygen content per unit blood volume. Secondary erythrocytosis was achievable with low iron stores, but only if serum iron was high-normal: Low serum iron levels were associated with reduced haemoglobin per erythrocyte, and overall arterial oxygen content was lower in iron deficient patients (median 16.0 [IQR 14.9, 17.4]mls/dL compared to 18.8 [IQR 17.4, 20.1]mls/dL, p<0.0001). Exercise tolerance appeared unrelated to SaO2 but was significantly worse in patients with lower oxygen content (p<0.0001). A pre-defined athletic group had higher Hb:SaO2 and serum iron:ferritin ratios than non-athletes with normal exercise capacity. PAVM embolisation increased SaO2, but arterial oxygen content was precisely restored by a subsequent fall in haemoglobin: 86 (87.8%) patients reported no change in exercise tolerance at post-embolisation follow-up.

SIGNIFICANCE

Haemoglobin and oxygen measurements in isolation do not indicate the more physiologically relevant oxygen content per unit blood volume. This can be maintained for SaO2 ≥78.5%, and resets to the same arterial oxygen content after correction of hypoxaemia. Serum iron concentrations, not ferritin, seem to predict more successful polycythaemic responses.

Ischaemic strokes in patients with pulmonary arteriovenous malformations and hereditary hemorrhagic telangiectasia: associations with iron deficiency and platelets

Background

Pulmonary first pass filtration of particles marginally exceeding ∼7 µm (the size of a red blood cell) is used routinely in diagnostics, and allows cellular aggregates forming or entering the circulation in the preceding cardiac cycle to lodge safely in pulmonary capillaries/arterioles. Pulmonary arteriovenous malformations compromise capillary bed filtration, and are commonly associated with ischaemic stroke. Cohorts with CT-scan evident malformations associated with the highest contrast echocardiographic shunt grades are known to be at higher stroke risk. Our goal was to identify within this broad grouping, which patients were at higher risk of stroke.

Methodology

497 consecutive patients with CT-proven pulmonary arteriovenous malformations due to hereditary haemorrhagic telangiectasia were studied. Relationships with radiologically-confirmed clinical ischaemic stroke were examined using logistic regression, receiver operating characteristic analyses, and platelet studies.

Principal Findings

Sixty-one individuals (12.3%) had acute, non-iatrogenic ischaemic clinical strokes at a median age of 52 (IQR 41–63) years. In crude and age-adjusted logistic regression, stroke risk was associated not with venous thromboemboli or conventional neurovascular risk factors, but with low serum iron (adjusted odds ratio 0.96 [95% confidence intervals 0.92, 1.00]), and more weakly with low oxygen saturations reflecting a larger right-to-left shunt (adjusted OR 0.96 [0.92, 1.01]). For the same pulmonary arteriovenous malformations, the stroke risk would approximately double with serum iron 6 µmol/L compared to mid-normal range (7–27 µmol/L). Platelet studies confirmed overlooked data that iron deficiency is associated with exuberant platelet aggregation to serotonin (5HT), correcting following iron treatment. By MANOVA, adjusting for participant and 5HT, iron or ferritin explained 14% of the variance in log-transformed aggregation-rate (p = 0.039/p = 0.021).

Significance

These data suggest that patients with compromised pulmonary capillary filtration due to pulmonary arteriovenous malformations are at increased risk of ischaemic stroke if they are iron deficient, and that mechanisms are likely to include enhanced aggregation of circulating platelets.

Arterio-venous shunts or low oxygen utilization?

An idea of arteriovenous shunts (AVS) was proposed for explanation of dynamic regulation of oxygenation and venous hyperoxia. A formula enabling calculation of AVS and real CO 2 production has recently been derived by comparing data of arterial and venous blood gases. Regarding venous hyperoxia, there is a need to differentiate capillary to tissue transport defect (low oxygen utilisation-LOU) from AVS, which may exist simultaneously. The AVS may be associated with normal or relatively high oxygen utilization from the capillary vessels and increased CO2 production. AVS is proposed to carry protective and ‘stealing’ properties including renal, cardiac, and pulmonary hemodynamic. Calculations of the AVS may be important for dynamic assessment of vascular and metabolic status and in emergency medicine.

Periumbilical uptake of Tc-99m MAA on lung perfusion scanning in a patient with superior vena cava obstruction

A 25-year-old woman with severe parenchymal lung disease of unknown etiology and existing for more than a decade was referred for ventilation-perfusion scintigraphy because of suspicion of pulmonary embolism. Both ventilation and perfusion images showed, apart from perfusion defects from her severe lung disease, a left apical pneumothorax and signs of recurrent pneumonia of the left lower lobe. Noteworthy was the periumbilical uptake of the Tc-99m macroaggregated albumin (MAA). Her medical history revealed iatrogenic superior vena cava (SVC) obstruction. In this case, the main collateral pathway of portosystemic shunting is probably, after recanalization of the left umbilical vein, a network of smaller paraumbilical veins.

Quantitative lung perfusion scintigraphy and detection of intrapulmonary shunt in liver cirrhosis

OBJECTIVE

Frequent association between liver cirrhosis and hypoxemia has been well documented. It is mostly attributable to intrapulmonary shunt due to dilation of pulmonary vasculature. We performed quantitative lung perfusion scintigraphy to detect an intrapulmonary shunt in cirrhosis patients.

METHODS

Prior to injection, Tc-99m MAA was applied to thin layer chromatography for quality control. Three cirrhosis patients who had hypoxemia were examined as well as 11 control subjects. After i.v. injection of Tc-99m MAA, whole body anterior and posterior images were taken at 5 min in patients with cirrhosis and at 8 time points up to 60 min in control subjects. Regions of interest were placed at the bilateral lungs and the whole body, and pulmonary accumulation was calculated.

RESULTS

All the control subjects demonstrated more than 90% of radioactivity in the lungs until 20 min. In contrast, all the patients showed values less than 80% at 5 min. In the cirrhosis patients with hypoxemia, the presence of intrapulmonary shunt was confirmed on quantitative lung perfusion scan. In control subjects, pulmonary accumulation of Tc-99m MAA dropped as a function of time and became less than 90% after 30 min.

CONCLUSION

The timing of measurements is essential in evaluating intrapulmonary shunt.

Pulmonary arteriovenous malformations: effect of embolization on right-to-left shunt, hypoxemia, and exercise tolerance in 66 patients

OBJECTIVE

This study assessed the effect and safety of percutaneous transcatheter coil embolization of pulmonary arteriovenous malformations.

MATERIALS AND METHODS

In 58 (88%) of 66 patients, all malformations with feeding vessels greater than or equal to 3 mm in diameter were embolized with steel coils. Arterial oxygen saturation at rest and exercise, intrapulmonary right-to-left anatomic shunt fraction ((99m)Tc-macroaggregate injection), maximum exercise capacity (incremental work rate test), and pulmonary function were measured before and after embolization. Complications were analyzed.

RESULTS

Three categories of patients were identified. Patients in group 1 (27%) had complete occlusion of all angiographically visible pulmonary arteriovenous malformations; patients in group 2 (61%) had complete occlusion of all malformations with feeding vessels greater than or equal to 3 mm in diameter, but with smaller lesions persisting; and patients in group 3 (12%) had incomplete embolization, with feeding vessels greater than or equal to 3 mm in diameter remaining. The mean right-to-left shunt after embolization was least in group 1 (7%), intermediate in group 2 (10%), and greatest in group 3 (19%). Arterial oxygen saturation and right-to-left shunt fraction returned to normal levels (>96% and <3.5%, respectively) in 33% of patients. A significant improvement occurred after embolization in carbon monoxide diffusing capacity per unit of alveolar volume and in exercise capacity in 16 and 10 patients, respectively. In 93 procedures, 12 complications (13%) occurred.

CONCLUSION

Coil embolization of pulmonary arteriovenous malformations is effective in reducing right-to-left anatomic shunt fraction and in improving arterial oxygenation. Coil embolization of pulmonary arteriovenous malformations is well tolerated and has a low complication rate.

Hepatopulmonary syndrome: a prospective study of relationships between severity of liver disease, PaO(2) response to 100% oxygen, and brain uptake after (99m)Tc MAA lung scanning

BACKGROUND

Because of the spectrum of intrapulmonary vascular dilation that characterizes hepatopulmonary syndrome (HPS), PaO(2) while breathing 100% oxygen varies. Abnormal extrapulmonary uptake of (99m)Tc macroaggregated albumin (MAA) after lung perfusion is common.

GOAL

To describe relationships between (1) severity of liver disease measured by the Child-Pugh (CP) classification; (2) PaO(2) while breathing room air (RA) and 100% oxygen on 100% oxygen; and (3) extrapulmonary (brain) uptake of (99m)Tc MAA after lung scanning.

METHODS AND PATIENTS

We prospectively measured PaO(2) on RA, PaO(2) on 100% oxygen, and brain uptake after lung perfusion of (99m)Tc MAA in 25 consecutive HPS patients.

RESULTS

Mean PaO(2) on RA, PaO(2) on 100% oxygen, PaCO(2) on RA, and (99m)Tc MAA brain uptake were similar when categorized by CP classification. Brain uptake was abnormal (> or = 6%) in 24 patients (96%). Brain uptake was 29 +/- 20% (mean +/- SD) and correlated inversely with PaO(2) on RA (r = -0.57; p<0.05) and PaO(2) on 100% oxygen (r = -0.41; p<0.05). Seven patients (28%) had additional nonvascular pulmonary abnormalities and lower PaO(2) on 100% oxygen (215+/-133 mm Hg vs 391+/-137 mm Hg; p<0.007). Eight patients (32%) died. Mortality in patients without coexistent pulmonary abnormalities was associated with greater brain uptake of (99m)Tc MAA (48+/-18% vs 25+/-20%; p<0.04) and lower PaO(2) on RA (40+/-7 mm Hg vs 57+/-11 mm Hg; p<0.001).

CONCLUSION

The degree of hypoxemia associated with HPS was not related to the CP severity of liver disease. HPS patients with additional nonvascular pulmonary abnormalities exhibited lower PaO(2) on 100% oxygen. Mortality was associated with lower PaO(2) on RA, and with greater brain uptake of (99m)Tc MAA.

Intrapulmonary arteriovenous shunting may be a universal phenomenon in patients with the superior cavopulmonary anastomosis: a radionuclide study

OBJECTIVE

To evaluate the extent of intrapulmonary right to left shunting in children after bidirectional cavopulmonary anastomosis (BCPA).

DESIGN

Prospective study of patients who underwent BCPA in a single centre.

PATIENTS

17 patients with complex cyanotic congenital cardiac malformations who underwent BCPA at 1-45 months of age (median 21 months) were evaluated 15-64 months postoperatively (median 32 months). Five children between 1 and 10 years (median 5 years) with normal or surgically corrected intracardiac anatomy and peripheral pulmonary circulation who required V/Q scanning for other reasons were used as controls.

INTERVENTIONS

All patients underwent cardiac catheterisation to exclude angiographically demonstrable venovenous collaterals followed by pulmonary perfusion scanning using (99m)technetium ((99m)Tc) labelled albumen microspheres to quantify the intrapulmonary right to left shunt.

MAIN OUTCOME MEASURE

Percentage of intrapulmonary right to left shunt.

RESULTS

The mean (SD) level of physiological right to left shunting found in the control group was 5.4 (2.3)%. All patients with BCPA showed the presence of a significantly higher level of intrapulmonary shunting (26.8 (16.9)%, p < 0.001). The degree of shunting was significantly increased in the subgroup of 11 patients with BCPA as the only source of pulmonary blood flow (34.9 (15.8)%), when compared to the six remaining patients with an additional source of pulmonary blood supply (12.0 (2.6)%, p < 0.001). There was a negative correlation between age at BCPA and the shunt percentage found in the patients with a competitive source of pulmonary blood flow (r = -0.63, p < 0. 01).

CONCLUSIONS

Intrapulmonary right to left shunting develops in all patients following BCPA. This may be caused by a sustained and inappropriate vasodilatation resulting from absence or decreased levels of a substance that inhibits pulmonary vasodilatation. Augmenting BCPA with an additional source of blood flow containing hepatic factor limits the degree of intrapulmonary arteriovenous shunting and may help provide successful longer term palliation.

Embolotherapy in the bronchial and pulmonary circulations

This two-part article first discusses the role of bronchial artery transcatheter embolotherapy in the management of patients with hemoptysis. Following this discussion, the authors review pulmonary arteriovenous malformations, their embolization, follow-up protocols, and outcome criteria as currently practiced at the authors' Vascular Malformation Center.

Sensitivity and specificity of radioisotope right-left shunt measurements and pulse oximetry for the early detection of pulmonary arteriovenous malformations

STUDY OBJECTIVES

To assess the effectiveness of pulse oximetry and radioisotope measurement of right-to-left (R-L) shunt for the early detection of pulmonary arteriovenous malformations (PAVMs) in patients with hereditary hemorrhagic telangiectasia (HHT).

DESIGN

Patients with HHT had serial measurements of the following: (1) arterial oxygen saturation (SaO2) by pulse oximetry in erect and supine positions, and on maximal exercise using cycle ergometry; (2) quantitative radioisotope measurements of R-L shunt using IV 99mTc-labeled macroaggregates of albumin; and (3) routine pulmonary function. After percutaneous transcatheter embolization of all PAVMs with feeding vessel diameters > 3 mm, residual PAVMs were assessed with selective digital subtraction pulmonary angiography. Using postembolization angiography as the "gold standard," SaO2 and radioisotope shunt measurements after embolization were analyzed retrospectively using logistic regression to assess the ability of each test to predict for the presence of residual PAVMs.

RESULTS

Of the 66 patients included, 40 had small PAVMs remaining postembolization. Using univariate logistic regression, radioisotope shunt and erect saturation showed a significant relationship with the presence of residual PAVMs (p=0.001, 0.005, respectively). Erect SaO2 < or = 96% had 73% sensitivity and 35% specificity for detecting PAVMs. Radioisotope shunt >3.5% of cardiac output had 87% sensitivity and 61% specificity for detecting PAVMs.

CONCLUSIONS

These results confirm that noninvasive measurements are useful in the screening of patients with HHT for the presence of PAVMs without need for angiography and its associated risks, and that radionuclide scanning is better than pulse oximetry.

Pulmonary arteriovenous malformations

Pulmonary arteriovenous malformations (PAVMs) are uncommon lesions, but are the cause of considerable morbidity and occasional mortality. They most commonly occur in association with hereditary haemorrhagic telangectasia and screening of families with this condition is therefore important. Embolization of PAVMs by coils is a well tolerated effective procedure with a low complication rate in skilled hands. Treatment results in both symptomatic and physiological improvement, and evidence for a reduction in stroke and cerebral abscess is accumulating. Radiological techniques now represent the primary treatment of choice, with surgical resection rarely required.

Spontaneous improvement in a patient with the hepatopulmonary syndrome assessed by serial exercise tests

A 37 year old patient with chronic active hepatitis progressing to cirrhosis presented with increasing breathlessness and was found to be hypoxic with finger clubbing. A progressive exercise study with measurement of oxygen saturation (SaO2) showed abnormally high ventilation and desaturation to 81% at 100 W. Serial studies over nearly two years showed, first, deterioration, then improvement with lower ventilation and higher saturation levels at all work loads. This could not be correlated with any change in treatment with azathioprine, prednisolone, or propranolol.

Oxygen and 99mTc-MAA shunt estimations in patients with pulmonary arteriovenous malformations: effects of changes in posture and lung volume

BACKGROUND

Patients with arteriovenous malformations are routinely monitored with arterial oxygen saturation (SaO2) estimations (breathing air) from which an oxygen shunt fraction can be calculated. This simple estimation has been compared with an anatomically defined estimate of the right to left shunt using a radioisotopic method. The fall in SaO2 which occurs in patients with pulmonary arteriovenous malformations in the erect posture and at high lung volumes was used to test the ability of SaO2 alone to follow changes in right to left shunt.

METHODS

Radiolabelled albumin macroaggregates (99mTc-MAA) or microspheres (MS) were injected intravenously and kidneys and lungs were imaged. The shunt fraction (QS/QTTc) in the supine position at functional residual capacity (baseline) was obtained by quantifying right kidney radioactivity. On standing or while breath holding at total lung capacity, shunt fraction was calculated from baseline QS/QTTc and from lung counts and the injected dose. Arterial oxygen saturation (SaO2) was recorded by a pulse oximeter for calculation of the oxygen shunt (QS/QTO2) (breathing air).

RESULTS

In the postural study (n = 8) SaO2 decreased from a mean (SD) value of 89 (5)% supine to 80 (6)% erect, corresponding to QS/QTO2 28 (8)% and 44 (8)% respectively. QS/QTTc increased from 28.7 (10.3)% to 39 (14.3)%. In the lung volume study (n = 8) QS/QTTc increased from 16.6 (11.5)% at functional residual capacity to 23.3 (11.9)% at total lung capacity while QS/QTO2 increased from 19.5 (7.5)% to 25.9 (10.6)% respectively. When all measurements were compared for QS/QTTc% and QS/QTO2% (n = 32) the difference in the mean values was 2.5% (absolute) and the limits of agreement between the two methods were +38% to -18% (relative). In neither the postural nor the volume study did delta (QS/QTO2) reliably predict delta (QS/QTTc)%.

CONCLUSIONS

In pulmonary arteriovenous malformations the simple physiological shunt calculated from SaO2 breathing air agreed well with the anatomical right to left shunt measured with 99mTc-MAA, but predicted poorly the changes in anatomical shunt induced by postural or lung volume changes.

Quantification of right to left shunt at rest and during exercise in patients with pulmonary arteriovenous malformations

BACKGROUND

Current treatment of patients with pulmonary arteriovenous malformations requires serial embolisations by means of steel coils or balloons. Measurement of right to left shunt is the most specific index of response to treatment. A new method of measuring shunt has been developed that is less invasive than traditional methods.

METHODS

Right to left pulmonary shunt (expressed as percentage of cardiac output) was measured at rest in 19 patients with pulmonary arteriovenous malformations and six normal subjects by using intravenously injected albumin microspheres labelled with technetium-99m. The technique was compared with a simultaneous shunt measurement in subjects breathing 100% oxygen while they rested. The microsphere technique was adapted to measure the right to left shunt during exercise in 12 patients and five normal subjects with a new method of quantification.

RESULTS

The mean (SD) shunt at rest as measured by the microsphere method was 23.2% (15.6%) in the patients and 2.7% (1.2%) in the normal subjects. When these values were compared with those of the 100% oxygen method the difference in mean values was 1% and the limits of agreement between the two methods -32% to +45%. The microsphere method is less invasive (arterial blood gas sampling is not required), quicker, and more comfortable for patients than the 100% oxygen method. In five of the normal subjects the mean (SD) 99mTc microsphere shunt increased from 2.9% (1.3%) at rest to 5.1% (2.9%) during exercise. In the 12 patients studied during exercise the shunt increased from 33.7% (12.7%) at rest to 41.7% (13.3%) during exercise in eight but decreased from 22.6% (2.4%) at rest to 17.6% (2.2%) during exercise in four. Arterial desaturation during exercise correlated with change in the size of the right to left shunt during exercise (r = +0.80).

CONCLUSIONS

The microsphere method allows measurement of right to left shunt at rest and during exercise. Serial measurements at rest provide a simple, safe assessment of the physiological response to embolisation in patients with pulmonary arteriovenous malformations.

Pulmonary nuclear medicine

This article reviews the contribution made by nuclear imaging to the assessment, diagnosis and monitoring of patients with respiratory disease. It focuses on several specific areas including the diagnosis of pulmonary embolism, the investigation of intrapulmonary infection and neoplasm and the role of positron emission tomography (PET) scanning.

Coil embolization of pulmonary arteriovenous malformations

Pulmonary arteriovenous malformations (PAVMs) are uncommon lesions that can be treated by surgery or interventional radiology. Forty-four PAVMs in 11 patients were occluded by transcatheter coil embolization with only one symptomatic complication, deep venous thrombosis, attributable to the procedure. There was a significant improvement in symptoms and a reduction in pulmonary AV shunting in the 9 patients in whom embolization of all visible discrete lesions was successfully completed. Coil embolization is an effective alternative to other methods of treating PAVMs.