Left atrial dissection: an almost unknown entity

Abstract

Left atrial dissection is an exceedingly rare but potentially fatal complication of cardiac surgery. It is most commonly associated with mitral valve surgery, including both replacement and repair, with a reported incidence rate of 0.16%. However, other cardiac surgical or catheter-based interventional procedures are also known as potential predisposing factors. The time of presentation from the cause of dissection varies extremely, ranging from immediate occurrence up to 20 years later. The dissection forms a large cavity between the endocardium and epicardium of the left atrium, causing obliteration of the left atrial cavity and resultant haemodynamic compromise, which almost always requires immediate surgical intervention. In contrast, left atrial dissection without haemodynamic instability can often be managed non-operatively with satisfactory outcomes. This article reviews this rare but relevant clinical entity to further elucidate the incidence, pathogenesis, clinical course, management and outcome of left atrial dissection.

Left atrial dissection, Mitral valve surgery, Transoesophageal echocardiography

INTRODUCTION

Left atrial dissection (LatD), an exceedingly rare complication of cardiac surgery, is defined as a false, blood-filled cavity or lumen from the mitral annular area to the left atrial free wall or interatrial septum, creating a new chamber with or without communications into the true left atrium, and is most commonly associated with mitral valve surgery [1]. Most previous reports describing LatD were anecdotal or single case reports without extensive discussion of the pathogenesis underlying this complication. True incidence, aetiology, pathophysiology, clinical course and management are poorly understood. LatD can be caused by any cardiac interventions, including both surgical and catheter-based, that involve manipulation of the left atrium. Varying presentation and clinical course are its unique characteristics. LatD may be fatal, resulting in haemodynamic collapse and death [2]. We previously reported our series of LatD and proposed a contained atrioventricular (AV) separation as the mechanism of LatD development after mitral valve surgery [2].

The purpose of our review is to better define the aetiology, pathogenesis, clinical course and surgical management of LatD to improve the recognition and outcome of this rare but relevant complication.

METHOD

A literature search of the National Library-based Pub Med and Ovid was performed. The search was limited to English articles. Diagnostic reports with no discussion of patient treatment were excluded. The article search identified 69 reports comprising 87 patients from 1979 to 2014 [1–71]. The case reports of patients from these articles are summarized in Table 1.

Table 1:

Patient demographics and suggested cause of left atrial dissection

Total number of cases	87
Age (n = 86)	62.1 ± 13.1 years
Male:female (n = 86)	39:47 (45%:55%)
Suggested aetiology
Mitral valve surgery	49 (56.3%)
Replacement	41 (47.1%)
Repair	8 (9.2%)
Spontaneous	9 (10.3%)
Cardiac amyloidosis	3 (3.5%)
Infectious endocarditis	1 (1.2%)
Radiofrequency ablation	7 (8.1%)
PCI	6 (6.9%)
Aortic valve surgery	4 (4.6%)
Myocardial infarction without PCI	3 (3.5%)
Coronary artery bypass grafting	3 (3.5%)
Cardiac mass excision	2 (2.3%)
Cardiac blunt trauma	2 (2.3%)
Pulmonary vein cannulation	1 (1.2%)
Left ventricular aneurysm repair	1 (1.2%)

PCI: percutaneous coronary intervention.

AETIOLOGY

A variety of aetiologies has been suggested in previous reports, but a detailed discussion elucidating the pathogenesis of LatD has been limited. Aetiologies or precipitating factors can be categorized into two categories: a surgical origin and a non-surgical origin. The latter is mainly caused by catheter-based cardiac interventions or spontaneous LatD.

Surgical aetiology

LatD has been mostly described as a complication associated with mitral valve surgery and can occur in both the trans-septal and the standard right lateral approach [1, 3, 4]. LatD can be caused whether the primary procedure is mitral replacement or repair for either degenerative, myxomatous or rheumatic heart disease. Severe calcification of the mitral annulus may be contributory [5, 6]. Aside from mitral procedures, aortic valve replacement (AVR) [7–9], coronary artery bypass grafting (CABG) [2, 10, 11], left ventricular aneurysmectomy [12], pulmonary vein cannulation [13] and cardiac mass excision [14, 15] have been associated with LatD. Partial AV separation is the probable pathogenesis of LatD associated with mitral valve procedures [2], although non-mitral cardiac surgeries quite remote from the AV junction can cause a LatD because of the creation of a small entry tear in the left atrial endocardium. Tissue fragility, such as collagen vascular disease and chronic steroid use, were also suggested [16] but are probably secondary rather than primary causative factors. On the contrary, LatD does not seem to be related to the type of implanted valve prosthesis. The correlation between left atrial size and incidence of LatD is unclear, but is likely not to be an aetiological factor.

Non-surgical aetiology

There have been non-cardiac surgical aetiologies described in the literature, including myocardial infarction [1, 17], percutaneous coronary intervention (PCI) [18, 19], radiofrequency ablation (RFA) [21, 22] and blunt cardiac trauma [1]. There were also 7 cases of spontaneous LatDs without any intracardiac manipulations [5, 22–26]. These spontaneous cases were attributed to underlying pathology including 3 cases of amyloid light-chain amyloidosis [23, 26], and 2 cases of severe mitral annular calcification [5, 6], 1 of was complicated by infectious endocarditis. Infection and necrosis of a heavily calcified posterior mitral annulus probably led to the formation of a dissection. Interestingly, LatD caused by RFA has been recently increasingly reported secondary to the increasing use of transatrial catheter ablation procedures. RFA entails catheter manipulation within or adjacent to the left atrium [27]. One of the LatDs caused by catheter ablation was complicated by a right superior pulmonary vein laceration, which was confirmed as the entry of the dissection intraoperatively [28]. Periprocedural concomitant anticoagulation during ablative therapy may contribute to the occurrence of LatD as well.

Pathogenesis and pathophysiology of LatD

The pathogenesis of LatD may be multifactorial. The clinical course of LatD varies from a self-limited stable disease managed conservatively to a devastating dissection with catastrophic outcomes, suggesting two distinct entities, although a clear separation into either category is often difficult.

LatD begins with an initial insult to the left atrial endocardium with entry of pressurized blood to create the dissection within the left atrial wall. In mitral valve surgery, overly aggressive debridement of the posterior annulus or subvalvular apparatus, oversizing of the prosthesis, inappropriate suturing or intense traction applied on the annulus might all be contributory as a cause of laceration of the annulus or bleeding from the AV groove [29]. Inadequate reversal of anticoagulation may exacerbate the dissection.

The presence of a pressurized inflow into the entry of the dissection, which can originate from the left ventricle, left ventricular outflow tract and retrograde cardioplegia infusion, is likely to be playing an important role in the pathogenesis of LatD. The close proximity of the circumflex artery and coronary sinus to the posterior wall of the left atrium, AV groove and mitral annulus is another important factor for the development of LatD. LatD due to RFA may be caused by creation of an endocardial flap of the left atrial wall due to a stiff wire manipulation [20, 21, 27, 28, 30, 31]. PCI to the circumflex or distal right coronary artery, retrograde cardioplegia injection through a malpositioned coronary sinus catheter, pulmonary vein cannulation, mechanical external compression for cardiopulmonary resuscitation and blunt cardiac trauma can all cause an entry within the myocardium and form a large cavity between the left atrial endocardium and epicardium by receiving a pressurized inflow. Typically, coronary sinus injuries are caused by forceful catheter insertion or repositioning attempts resulting in punctation or perforations of the coronary sinus wall [72]. Bright-red bleeding from the back of the heart and inability to achieve adequate pressure during cardioplegia infusion are usually seen. However, the coronary sinus is a low-pressure system and LatD is unlikely to occur with this injury alone without a source of pressurized inflow. Coronary sinus injury and its major rupture usually occur in the middle section of the coronary sinus, which can potentially cause a large AV groove haematoma, which is most relevant in patients with septal hypertrophy [72]. Avoidance of forceful catheter insertion and distortions of the coronary sinus lumen and careful monitoring of the infusion pressure are important for prevention of these injuries. Cardiac massage has been described as a possible aetiological factor of LatD [32], although this patient in the report had undergone MVR 5 years prior to the episode of cardiac arrest. The mitral prosthesis had dehisced due to the cardiac compression and the resultant shear force might have created dissection in the left atrium.

Interestingly, LatD most frequently occurs along the posterior wall of the left atrium (63/78 cases; 80.8%). Unlike the anterior leaflet, the attachment of the posterior leaflet to the annulus is primarily muscular with little or no fibrous tissue. In addition, the attachment of the anterior leaflet is tougher and has fewer calcifications than that of the posterior leaflet [42, 73]. The AV groove also provides a naturally weakened transitional area vulnerable to overdistension and forceful manipulation [74]. We postulate that this anatomical difference accounts for the tendency of occurrence of LatD on the posterior wall in patients undergoing mitral valve surgery. In contrast, in patients undergoing AVR, LatD tends to occur along the interatrial septum and anterior wall of the left atrium rather than the posterior wall [8, 9, 16]. Disruption of the non-coronary annulus in the region of aortic/mitral valve continuity can occur during AVR, allowing pressurized inflow into the dissected layer of the left atrium [8]. The atrial myocardium in the aortoatrial space is formed of loosely arranged muscle bundles that allow for the expansion of the haematoma [33]. Expansion of the dissected cavity may be dependent on pressurized inflow of blood.

Haemodynamic instability is mainly secondary to obstruction of mitral valve inflow or pulmonary vein orifice and eventual congestive heart failure and low-output syndrome. The left atrium can be easily compressed by intramural haematoma and, therefore, could lead to impairment of pulmonary venous return and thereby failure to wean off CPB [34]. LatD may be classified as a subtype of left ventricular rupture type I [1], which occurs at the posterior AV groove, given the similarity of the pathogenesis. The difference between mitral surgery-induced LatD and left ventricular rupture may be the status of rupture free or directed towards the left atrium, leading to spread of tissue and formation of a cavity within the left atrial wall.

INCIDENCE

The incidence rate of LatD in our previously reported series was 0.16% of mitral valve patients and 0.02% of isolated CABG patients [2]. Most of the available information is based on isolated cases [1]. However, LatD is currently becoming more recognized along with the utilization of perioperative transoesophageal echocardiography (TEE). Interestingly, LatD has been increasingly reported over the last 10 years, possibly because of the routine use of TEE and improvement of diagnostic detectability and accuracy. In contrast, this complication was almost not recognized until the 1990s when TEE became the routine intraoperative monitoring technique and diagnostic tool for the management of cardiac surgical patients. In fact, the diagnosis of LatD in the literature before the era of TEE was based on gross intraoperative findings or incidental autopsy findings [32]. It is obvious that many other cases have never been reported. Furthermore, LatD is often labelled differently, such as a left atrial (intramural) haematoma and AV groove haematoma in some reports, although these appeared to be the same pathology as the ‘LatD’ in this article. Despite the potential underreporting, it is still an exceedingly rare complication.

PRESENTATION AND DIAGNOSIS

It is important to differentiate two distinct clinical features: stable and unstable LatD. LatD can demonstrate a variety of presenting symptoms, including chest pain, dyspnoea, palpitations, fatigue, syncope and cardiac arrest [1–3, 6, 35–37]. One of the most common presentations of LatD is rapid haemodynamic change with weaning of CPB [2] (Table 2). Obstruction of the pulmonary veins and mitral inflow causing congestive heart failure and low-output syndrome are pathognomonic features and diagnosed on intraoperative TEE. Conversely, patients are sometimes asymptomatic and found to have LatD incidentally on a routine follow-up examination [14, 38]. Objective findings include a systolic jet flow between the left ventricle and the left atrium on TEE, which may be detected on auscultation as a systolic murmur.

Table 2:

Clinical presentation, management and outcomes of left atrial dissection

Time to presentation after initial insults (n = 71)	<24 h	31 (43.7%)
	Days	21 (29.6%)
	Months	7 (9.9%)
	Years	12 (16.9%)
Clinical presentation (n = 85)	Dyspnoea	23 (27.1%)
	Intraoperative haemodynamic instability	19 (22.4%)
	Haemodynamic instability on presentation	18 (21.2%)
	No symptoms	10 (11.8%)
	Chest pain	5 (5.9%)
	Tachybradyarrhythmia	4 (4.7%)
	Intraoperative incidental finding	4 (4.7%)
	Syncope	1 (1.2%)
	Dysphagia	1 (1.2%)
Location of LatD (n = 78)	Posterior wall	63 (80.8%)
	Interatrial septum	11 (14.1%)
	Anterior wall	4 (5.1%)
Treatment	Surgical repair	63 (72.7%)
	Primary/patch repair	43 (68.3%)
	Prosthesis explantation and reimplantation	15 (23.8%)
	Unknown detail	5 (5.8%)
	Conservative management	21 (24.1%)
	Incidental finding on necropsy	3 (3.5%)
Outcomes	Overall mortality	12 (13.8%)
	Mortality after surgical intervention for LatD (n = 63)	8 (12.7%)

LatD: left atrial dissection.

The time of presentation of LatD varies, ranging from immediately intraoperative to 20 years after the original precipitating factors (Table 1). It can be classified by time patterns: early, delayed and late presentation. It mostly occurs shortly after the causative procedure (73.3%), and a delayed (9.9%) or late (16.9%) presentation of LatD seems to be less common. TEE is demonstrated to be the technique of choice [3] and is mandatory to establish the diagnosis of LatD. The efficacy and diagnostic value of transthoracic echocardiography, computed tomography scan and magnetic resonance imaging may be limited. An entry of dissection or communication between the inflow and the left atrium on TEE, even in the presence of expanding dissection, is often difficult to visualize. The echocardiographic findings of LatD are quite confusing, resembling a left atrial mass and cardiac tamponade, especially when the dissection is focal and containing clots. Other differential diagnoses include conditions that can cause external compression of the left atrium such as hiatal hernia and oesophageal perforation. Cardiac tamponade secondary to coronary artery perforation is also an important differential diagnosis in patients undergoing PCI.

MANAGEMENT

No definitive criteria exist to help guide management of this rare entity. In fact, the prompt diagnosis of LatD is often difficult, given the often confusing clinical picture with haemodynamic instability. Afterload reduction in critical situations using intra-aortic balloon pumping may be beneficial. However, operative intervention is always indicated if haemodynamic collapse exists. In previous reports, prompt surgical repair was undertaken in most of the patients (73.4%; 63/87) (Table 2). In addition, most patients even with delayed or late presentation (>months from original procedures) required surgical intervention.

In 1985, Maeda et al. [39] first reported a surgical repair of LatD through a left thoracotomy. Since then, different surgical approaches have been described to repair LatD. The keys to the success of the surgical repair are the following: (1) to gain adequate evacuation of the haematoma; (ii) obliteration of the false lumen; and (iii) addressing the entry point, if identified [2]. It can recur even after surgical repair without addressing the communication, which can cause a persistent pressurized inflow [37]. The atrial wall tissue and mitral annulus are often friable and do not hold sutures adequately. Concomitant use of BioGlue adhesive and a bovine pericardial/synthetic patch may also be helpful. If explantation of the prosthesis is necessary, careful sizing of the valve for reimplantation is crucial. In our series, surgical repair was successful in all patients, with satisfactory early and midterm outcomes [2].

Conversely, surgical intervention may not be necessary with LatD without haemodynamic compromise, as seen in several reports (21/87; 24.1%) (Table 2). Therefore, haemodynamic instability, which is indicative of coexistent rapid expanding of the haematoma that can result in occlusion of the left atrial cavity, pulmonary veins or mitral inflow obstruction, is the critical factor that determines the necessity of surgical repair. Reversal of anticoagulation may be helpful for intraoperative LatD without haemodynamic instability [75].

OUTCOMES

The overall mortality rate in the reported literature was 13.8% (12/87). LatD does not seem to carry a high mortality rate if promptly diagnosed and managed. Serial imaging follow-up studies of non-operatively managed cases showed resolution of the dissected cavity, suggesting a remodelling process of the left atrial wall after initial insults [2].

CONCLUSION

LatD is an exceptionally rare and potentially devastating complication of cardiac surgery and interventional procedures. LatD may be more recognized with the routine use of intraoperative TEE monitoring and improvement in the accuracy of echocardiographic interpretation. One of the mechanisms of LatD secondary to mitral valve surgery is likely to be partial AV separation causing dissection of the layers of the posterior left atrium. Prompt intraoperative diagnosis and surgical repair are recommended in any case with haemodynamic compromise. In contrast, non-operative treatment is also effective in a stable patient in whom natural remodelling of the left atrium occurs.

Conflict of interest: none declared.