Atrial septal defect (ASD)

Illustrated Review with ECG, CXR, Echo Video, Cath Images

X-ray chest in atrial septal defect

X-ray chest PA view in atrial septal defect with pulmonary hypertension

(Click on the image for an enlarged view)

The main pulmonary artery (MPA) is grossly dilated. The right pulmonary artery (RPA) is also quite enlarged. Right atrial enlargement is seen as a shift of the cardiac contour to the right of the spine. Pulmonary vascularity is increased and prominent end on vessels (End on) are also seen. Apex is upwards, suggesting a right ventricular configuration. All features suggest a large secundum atrial septal defect with a large left to right shunt producing severe pulmonary hypertension. Cardiomegaly on chest x-ray is suggestive of atrial septal defect in Eisenmenger syndrome, while it is unlikely in ventricular septal defect and patent ductus arteriosus. Cardiomegaly is mainly due to the grossly dilated right atrium in atrial septal defect. The right atrium is not enlarged in the other two varieties of Eisenmenger syndrome. In ventricular septal defect with large left to right shunt, the cardiac size comes down as pulmonary hypertension develops and the shunt decreases. Cardiomegaly in ventricular septal defect and patent ductus arteriosus with large left to right shunt are due to left ventricular enlargement. But this comes down with the development of pulmonary hypertension. That is why cardiomegaly is not a feature of Eisenmenger syndrome due to ventricular septal defect and patent ductus arteriosus. In patent ductus arteriosus, an additional feature on x-ray chest is the dilated aortic shadow. Inverted Y shaped ductal calcification may also be seen with patent ductus arteriosus and Eisenmenger syndrome.

X-ray chest PA view in atrial septal defect with pulmonary hypertension

Atrial septal defect with pulmonary hypertension

(Click on the image for a larger view)

X-ray chest PA view in atrial septal defect with severe pulmonary hypertension. Prominent main pulmonary artery, right pulmonary artery and left pulmonary artery (behind the main pulmonary artery) and end on views of dilated branch pulmonary arteries are seen. Echocardiography documented large secundum atrial septal defect (ASD) with severe pulmonary hypertension and bidirectional shunt across the ASD.

What is the importance of PR interval prolongation in secundum atrial septal defect (ASD)?

There is a higher incidence of sudden cardiac death (SCD) in familial ASD with prolongation of PR interval.

Crochetage sign in atrial septal defect

Crochetage sign in ASD

(Click on the image for an enlarged view)

Crochetage sign in atrial septal defect was described by Heller J et al [1] in 1996. It is a notch near the apex of the R wave in inferior leads. They noted a sensitivity of about 73% and specificity of 92% if the sign was present in all the three inferior leads. Early disappearance of the crochetage sign after surgical correction of atrial septal defect was found in 35% of cases even when the incomplete right bundle branch block (RBBB) pattern was persisting. The ECG illustrated above shows the notch at the apex of the R wave in leads II and aVF and a notch in the ascending limb of lead III.

This ECG also shows right atrial overload as evidenced by P wave amplitude of 0.3 mV in lead II. Incomplete RBBB pattern is seen as slurred S waves in lead I and rSrS pattern in V1.

Low atrial rhythm

(Click on the image for an enlarged view)

This ECG shows inverted P waves in inferior leads (II, III and aVF). This indicates that the atrial activation is spreading from below upwards. It is suggestive of a focus either in the low atrium or high junction. A mid junctional rhythm will have no visible P waves as the P wave will be within the QRS due to simultaneous activation of the atria and ventricles. In low junctional rhythm the P wave occurs after the QRS, in the ST segment and is inverted in inferior leads. In left atrial rhythm originating from the lower part, the P waves are inverted in inferior leads as well as lateral leads.

There is notching of the QRS complex in the inferior leads which suggest the crochetage sign in atrial septal defect. Low atrial rhythm can occur with sinus venosus atrial septal defect as the sinus node may be defective so that alternate focus arising in the low atrium gives the dominant rhythm. The PR interval is also shorter in low junctional and low atrial rhythm, more in the former than in the latter, due to obvious reasons.

ECG in atrial septal defect with severe pulmonary hypertension

Atrial septal defect with severe pulmonary hypertension

(Click on the image for a larger view)

ECG in atrial septal defect with severe pulmonary hypertension. rSR’ pattern is seen in V1 with a tall R’, possibly reflecting right ventricular hypertrophy. The strain pattern is extensive, from V1 to V6. RSR pattern is seen in III and aVF as well. The QRS duration is also increased. Echocardiogram in this case confirmed a large secundum atrial septal defect with severe pulmonary hypertension and bidirectional shunt.

ECG after surgical closure of ASD
irbbb-first-degree-av-block-small

(Click on the image for an enlarged view)

PR interval is prolonged and measures 280 msec. There is additional incomplete right bundle branch block with rSR’ pattern in V1 with a QRS width of 110 msec. This combination of first degree AV block with incomplete right bundle branch block is seen in familial atrial septal defect, which is transmitted in an autosomal dominant pattern. This means that 50% of first degree relatives have a chance to have atrial septal defect. In this individual there is no family history of atrial septal defect though a formal family study has not been done. Though this person had undergone surgical closure of the atrial septal defect three decades back, the abnormal ECG pattern is persisting.

Atrial septal defect (ASD)- colour Doppler echo

ASD on 2D echo

Echocardiographic image from subcostal four chamber view showing the atrial septal defect (ASD). Subcostal view is the ideal view for imaging atrial septal defect to exclude false echo dropouts which may be seen in apical four chamber view. This is because the imaging ultrasound beam is perpendicular to the septum in subcostal view while it is parallel the to the atrial septum in apical four chamber view. This ASD has good rims above and below, and could be suitable for device closure, which has to be decided after a trans oesphageal echocardiogram to assess all the rims.

ASD flow by colour Doppler

Colour Doppler flow mapping showing the red coloured flow across the atrial septum from left atrium (LA) to the right atrium (RA). The flow is red coloured because it is towards the echo transducer in this view. RV: right ventricle; LV: left ventricle. The flow reversal (blue colour and jet moving from RA to LA) can occur when there is severe pulmonary hypertension. Reverse flow across the atrial septal defect (right to left) can also be seen in total anomalous pulmonary venous connection.

Echocardiogram in ostium primum ASD with tricuspid regurgitation

Primum ASD

Echocardiogram in apical four chamber view of primum ASD

Echocardiogram in apical four chamber view demonstrating a primum atrial septal defect (primum ASD). RV: right ventricle; LV: left ventricle; RA: right atrium; LA: left atrium; Primum ASD is part of the AV canal defect and is sometimes called a partial AV canal defect. In AV canal defects the atrioventricular septum (AV septum) is absent and both AV valves are at the same level. Primum ASD is usually associated with a cleft of the anterior mitral leaflet (AML) which appears like an additional commissure in the parasternal short axis view. Cleft AML produces significant mitral regurgitation, which is an association of ostium primum ASD. A similar defect in the tricuspid valve can cause tricuspid regurgitation. Another association of an ostium primum ASD is the inlet or canal ventricular septal defect (VSD).

Primum ASD L - R Shunt

Colour Doppler echocardiogram showing left to right shunt in ostium primum ASD

This frame with colour flow mapping demonstrates the left to right shunt (L>R Shunt) across the primum ASD. Though the actual direction of the shunt is perpendicular to the direction of the beam, most of the blood moves from the left atrium across the ASD towards the tricuspid valve in a direction which is parallel to the beam and towards the transducer. That is why this flow is encoded red.

Primum ASD TR Jet

Apical four chamber view showing tricuspid regurgitation in primum ASD

Apical four chamber view demonstrating tricuspid regurgitation (TR jet) in a case of primum ASD. The bluish mosaic coloured jet is due to the blood flowing away from the transducer in systole. The mosaic indicates turbulent flow with aliasing since the velocity is above the Nyquist limit of the colour Doppler system. Nyquist limit is the maximum velocity which can be imaged by a particular system and is half of the pulse repetition frequency.

Echocardiogram video showing the primum atrial septal defect and the associated tricuspid regurgitation

Patent foramen ovale vs small ASD

Patent foramen ovale or small atrial septal defect?

Echocardiogram from subcostal view showing the interatrial septum with a small defect and left to right flow across. Red colour encodes flow towards the transducer at the top and hence a flow from left atrium (LA) to right atrium (RA). Whether it has to be called a small atrial septal defect (ASD) or a patent foramen ovale (PFO) is the question. Conventionally PFO is a valvular opening which closes when the blood tries to flow from the left atrium to the right atrium. In certain phases of the cardiac cycle or during a Valsalva manoeuvre, right to left flow of blood can occur across the PFO. This is thought to be the mechanism of paradoxical embolism and stroke in case of PFO. Left to right shunt can occur across a stretched open PFO when the right or left atrium enlarges due to another pathological condition which elevates the left atrial pressure. In this case there was an associated ventricular septal defect (VSD). But the size of the defect and the magnitude of the shunt across the VSD was not sufficient enough to produce volume overloading of the left sided chambers.

If there is a spontaneous left to right shunt through out the cardiac cycle, the defect is better considered as a tiny atrial septal defect rather than a PFO. The reason is that PFO by definition, is a valvular opening which permits shunting only right to left. PFO shunts can be detected by contrast echocardiography in which agitated saline is injected into a peripheral vein. If the contrast appears in the left atrium within three cardiac cycles, it is suggestive of right to left shunt across the PFO. Transesophageal echocardiography may be better for the demonstration of PFO because of higher resolution.

Transcranial Doppler studies will document these bubbles reaching the brain and hence the possibility of paradoxical embolism and stroke in case there is deep vein thrombosis. PFOs have also been associated with migraine like symptoms. Whether these are also related to paradoxical emboli has to be considered.

PFO closure has been recommended for the secondary prevention of stroke as well as for primary prevention of stroke in case of transient ischemic attacks. PFO closure device is similar to the ASD closure device, but differs in two aspects. The right atrial disc is larger, unlike the ASD device. The connecting piece between the two discs is of much lesser diameter compared to an ASD device. The technique of device delivery is similar to that of ASD device closure. Device closure is done under fluoroscopy in the cath lab with guidance of device position by transesophageal echocardiography.

Trans esophagealechocardiogram in atrial septal defect

Transesophageal echocardiogram (TEE) is useful in the evaluation of atrial septal defect (ASD) to assess the finer details while deciding on device closure. It is also useful in delineating ASDs which are not visible by transthoracic echocardiography (TTE) either due to poor echo window or due to odd location of the ASD as in sinus venosus ASD. TEE is often used in this context while evaluating pulmonary hypertension of obscure etiology in an adult. TEE probe being very near the heart without any intervening lung tissue, can give excellent images. Moreover, the short distance permits the use of higher frequency transducers with better image resolution. Usually higher frequency transducers cannot be used for TTE because of poor depth of ultra sound penetration at higher frequencies in an adult.

Atrial septal defect on trans esophageal echocardiography

Atrial septal defect on transesophageal echocardiography

TEE image in short axis view showing the aorta (Ao), part of the inter atrial septum (IAS) and the ASD. It can be seen that there is hardly any aortic rim (bald aortic rim). Part of the left atrium is seen above the IAS at the top (not marked in the figure). Below the IAS the large right atrium is visible. The TEE probe has a temperature sensor which senses both the subjects temperature as well as the probe temperature. Automatic cooling is initiated when the probe temperature goes above the cut off limit. A visible alert is also displayed when the probe heats up, requesting the operator to reduce the power output of the ultrasound beam. A trade off between visibility of images and the heating up of the probe is required in some cases. Since it is difficult to repeat TEE studies frequently, either continuous or frequent recording of TEE videos during the entire study will permit re-assessment by the same operator as well as an independent operator. TEE studies are invariably done in a fasting state and under topical anaesthesia of the oropharynx to reduce gag reflex. A mouth gag is needed to prevent biting and damage to the probe. ECG monitoring is needed to time the events in the cardiac cycle as well for the rhythm in sick individuals. Pulse Oximetry and facility for suction are also ideal. Pat. T: temperature of the subject; TEE T: TEE probe temperature. The dial shows the plane of imaging from 0-180 degrees (58 degrees in this image).

Two atrial septal defects with a smal segment of intervening septum

Two atrial septal defects with a small segment of intervening septum

Dual ASDs with a small intervening segment of atrial septum seen on TEE. The right atrium appears dilated. The total size of both ASDs taken together is quite large and not suitable for device closure.

Measurement of first ASD

Measurement of first ASD

First of the two ASDs being measured by calipers. The next image shows the measurements of both ASDs.

Measurements of both ASDs

Measurements of both ASDs

This image displays the measurements of both ASDs. One measures 17.5 mm and another measures 15.6 mm. The total will be 33.1 mm. The rims at both ends also appear deficient so that device closure may not be feasible in this case. Surgical closure will be ideal, provided that there is no features of irreversible pulmonary hypertension.

Transesophageal echocardiogram video in atrial septal defect, demonstrating poor aortic rim and dual atrial septal defects in another view.

Device closure of atrial septal defect (ASD)

Device closure of ASD

Device closure of ASD

Device closure of ASD is suitable for secundum ASD with a good rim all around for holding the two discs together. Trans esophageal echo (TEE) is done to assess the superior, aortic and mitral rims as well as the total septal length. It is ideal to have TEE guidance during the procedure as well. A guide wire is introduced through the femoral vein into the inferior vena cava and further through the right atrium across the ASD. The tip of the wire is placed in the pulmonary vein and a long venous sheath is introduced. Once the sheath is in position, the device attached to the delivery cable is introduced into the sheath under water to avoid air bubbles in the system. Once the device reaches the left atrium, the left atrial disc of the device is released first and brought in contact with the left atrial side of the ASD. When the position is judged ideal, the right atrial disc is allowed to form by withdrawal of the sheath. Once the two discs are in position with the waist across the ASD, slight wiggling is done to make sure that the device is perfectly fitting and has no tendency for dislodgement. Position is confirmed by TEE with special care to see that the device does not interfere with the function of the AV valves. Once everything is fine, the device is released by unscrewing the delivery cable. The device usually used is the Amplatzer device.

Device closure of ASD in older patients

Generally closure of atrial septal defect (ASD) is done in children and young adults. Benefits of device closure of ASD in older patients are not well documented. A recent study [2] involving 23 patients with ASD and aged 50 – 91 years, having ASD size between 16 to 36 mm reported favorable cardiac remodeling and improvement of functional class. The NYHA (New York Heart Association) functional class improved in 16 patients. They had significant improvement in 6 minute walk distance and mental health score. No major complications were noted in these ASD device recipients. They also had significant change in the left ventricular end diastolic and end systolic dimensions at one year after the closure. There was accompanying significant reduction in right ventricular end diastolic dimensions as expected. The improvement of left ventricular function was due to offsetting of the reverse Bernheim effect in which right ventricular dilatation causes a septal bulge and impedance to left ventricular function. Though some studies have shown transient increases in left atrial pressure and consequent pulmonary edema in elderly patients after ASD closure, due to a stiff left ventricle, the current study did not report any such instance. The authors concluded that ASD closure with devices is technically feasible and is associated with favourable cardiac remodeling and improvement in functional class in older patients.

Holt-Oram syndrome

Holt-Oram syndrome was described by Mary Holt and Samuel Oram as ‘ Familial heart disease with skeletal malformations’ [3]. The initial description was of familial atrial septal defects and abnormalities of the thumb and radial aspect of the upper limb. Simian thumb, in which the thumb lies in the same plane as the other fingers is a characteristic description. Terminal phalanx was curved and pointed inwards. The thumb can also be triphalangeal and finger like, with inability to oppose. Most severe form of upper limb dysplasia resembling phocomelia has also been reported. Atriodigital dysplasia was another name suggested for the Holt-Oram syndrome. The original family described had also cardiac conduction disturbances and arrhythmias.

Holt-Oram syndrome is inherited in an autosomal dominant pattern and the mutation is in the transcription factor TBX5. The mutation was described by Li QY et al in 1997 [4]. Though the most common cardiac anomaly is atrial septal defect of the secundum variety, other defects like ventricular septal defect have been described.Ventricular septal defect is of the muscular or trabecular variety. Cardiac malformations are seen in 75% of the affected family members. Carpal bone abnormalities are seen in all affected individuals, though it may be clinically silent and evident only radiologically.

Since it is an autosomal dominant mode of transmission, offspring have a 50% chance of being affected. But about 85% of cases of Holt-Oram syndrome have de novo mutations. Mutations in TBX5 account for up to 70% of cases of Holt-Oram syndrome.

References

  1. Heller J, Hagège AA, Besse B, Desnos M, Marie FN, Guerot C. “Crochetage” (notch) on R wave in inferior limb leads: a new independent electrocardiographic sign of atrial septal defect. Am Coll Cardiol. 1996 Mar 15;27(4):877-82.
  2. Khan AA, Tan JL, Li W, Dimopoulos K, Spence MS, Chow P, Mullen MJ.The impact of transcatheter atrial septal defect closure in the older population: a prospective study. JACC Cardiovasc Interv. 2010 Mar;3(3):276-81.
  3. Holt M, Oram S. Familial heart disease with skeletal malformations. Br Heart J. 1960 Apr;22:236-42.
  4. Li QY, Newbury-Ecob RA, Terrett JA, Wilson DI, Curtis AR, Yi CH, Gebuhr T, Bullen PJ, Robson SC, Strachan T, Bonnet D, Lyonnet S, Young ID, Raeburn JA, Buckler AJ, Law DJ, Brook JD. Holt-Oram syndrome is caused by mutations in TBX5, a member of the Brachyury (T) gene family. Nat Genet. 1997 Jan;15(1):21-9