Dual left anterior descending artery: diagnostic criteria and novel classification

Abstract

Duplication of the left anterior descending artery is an uncommon coronary anomaly. Since no proper classification has been established after the initial description and numerical classification by Spindola-Franco et al., many newer numbers have evolved with many overlapping and unclassified variants described in the literature. Identification and reasonable management strategies for dual left anterior descending artery (LAD) are crucial in preventing the long-term disastrous consequences of inadequate revascularization. Clinicians and diagnosticians should be aware of this specific angiographic-based congenital coronary abnormality of the LAD. We, therefore, sought a new, reasonable classification of the dual LAD system, which would clarify this ambiguity, which also has therapeutic implications.

Introduction

Generally, the left anterior descending artery (LAD) follows a predictable course and its congenital abnormalities are less frequent compared to the other coronary arteries [1, 2]. Dual LAD is a collective term that includes a group of anomalies where LAD duplicates either by splitting into two major divisions or by originating from two different ostial sources to supply the same territory in parts [3]. The incidence of dual LAD varies from 0.68 to 6% in different case series [4–6] which is always inadvertently diagnosed during coronary angiography. Upon its detection, the clinician should correlate the symptoms of patients to establish its clinical significance based on the aberrant course of dual LAD. Besides clinical guidance, correct knowledge of the nature of dual LAD and morphological characteristics of its subtypes is essential to the successful revascularization. The objective of this review was to create a consistent and systematic blend of alpha-numeric and descriptive classification of dual LAD with a therapeutic value.

Definitions

The following definitions were used for the novel classifications of the dual LAD to differentiate it from the other normal variations or anomalies of the LAD.

Normal LAD

Normal LAD originates from the left main coronary artery (LMCA) which emerges from the left coronary sinus (LCS) and courses towards the cardiac apex in the anterior interventricular sulcus (AIVS). The septal branches arise almost perpendicularly and supply mainly the anterior 2/3rd interventricular septum which is its characteristic feature. The diagonal branches are divided into two types, the majority of left ventricular (LV) diagonal branches which supply the anterolateral LV wall, and right ventricular (RV) diagonal branches, less in number which supply the anterior RV wall [1, 2, 7].

Parallel LAD and parallel diagonal

Sometimes the LAD runs a regular course in the AIVS but gives off a large diagonal branch that runs parallel to the LAD which does not re-enter the distal AIVS. This form of anatomy is colloquially known as a parallel LAD where a large diagonal branch supplies septal arteries and if, however, it does not give septal branches, it should be labeled as parallel diagonal [5, 8].

Split LAD

The word “split” or bifurcated LAD should be confined to variations of a LAD which originates entirely from the LCS like normal LAD and separates into two branches, both contributing in part or the entire region of its distribution (Fig. 1a–d). But the terms dual LAD and split LAD cannot be distinguished separately as their descriptions to a large extent overlap that we chose to use the term dual LAD for all of these LAD variants in our study [3].

Fig. 1.

a-d: Conventional coronary angiography of Group I dual LAD (case 1). LAO caudal views (a) demonstrated separate origins of LAD₁ (solid arrows) and LAD₂ (dashed arrows) with critical stenosis of the ostio-proximal segment of LAD₂. After the percutaneous coronary intervention, LAD₂ was visualized better (AP cranial, b; RAO caudal, c). It ran on the left ventricular side of AIVS and re-entered distally near the apex to continue beyond into the posterior interventricular sulcus (dashed line; d). LAD₁ predominantly supplied septal branches while LAD₂ gave rise to peri-apical septals while most of the diagonal branches arose from the LAD₂. LAD, left anterior descending artery; RAO, right anterior oblique; LAO, left anterior oblique; AIVS, anterior interventricular sulcus

Dual LAD

The term “dual or double LAD” is used for a variation of LAD, where two separate arteries supply a part or whole of its collective territorial destinations. Dual LAD anomaly is identified by the existence of two separate LAD components in the AIVS and usually identifies as a short LAD and a long LAD. This division of the LAD into the short LAD or LAD₁ and long LAD or LAD₂ corresponds to the usual course of single LAD in the AIVS based on their lengths [3, 4]. Generally, LAD₁ ends high in the proximal AIVS, but may occasionally stretch to the mid-AIVS (Fig. 2a, b). Although the proximal path of the LAD₂ is usually variable, extends outside of the AIVS, and can emerge from the right coronary sinus (RCS) from either the common or separate ostium of the right coronary artery (RCA), the constant or usual feature is that it enters the distal AIVS (Fig. 2c, d). The LAD₁ emanates primarily to proximal septal perforators, proximal LV diagonals, and occasionally RV diagonals, while the LAD₂ stems from distal septal perforators, distal LV diagonals, and even sometimes RV diagonals [3, 5].

Fig. 2.

a-d: Conventional coronary angiography of Group II dual LAD (case 2). The LAD₁ (dashed arrows) originated from the common LAD and terminated in proximal AIVS after supplying few septal branches (RAO and LAO cranial views; a, b). The angiography of the dominant RCA revealed non-obstructive plaques (c). Selective angiography of LAD₂ (solid arrow) which originated separately from the RCS demonstrated an initial slight upward horizontal course that gave rise to septal perforators and then turned downwards to supply the mid and distal interventricular septum (d). LAD, left anterior descending artery; RAO, right anterior oblique; LAO, left anterior oblique; RCA, right coronary artery; RCS, right coronary sinus

Hyperdominant LAD

Hyperdominant LAD is an anomaly in which the LAD wraps around the LV apex and extends to the territory supplied by the inferior interventricular artery along the posterior interventricular groove. There are various terminologies used to describe like super-dominant LAD, type IV LAD, or an anomalous origin of the inferior interventricular artery from the LAD [9]. One of our cases demonstrated the combination of dual LAD and hyperdominant LAD is not mentioned in the literature (Fig. 2d).

Historical aspects

• The first mention of a dual LAD found in the literature in 1939 was the case of Sir James Mackenzie, who had a dual LAD in addition to ischemic heart disease, described by Waterson et al. [10].

• In 1983, Spindola-Franco et al. published the first review and classification of dual LAD anomalies based on coronary angiography, which provided a primarily numerical method of classification [5].

• After the publication by Voudris et al. [11], describing this entity as a “double LAD,” Spindola-Franco and Greenberg reiterated in a letter to the editor the importance of a standard, uniform nomenclature to be used to avoid misunderstanding about this condition [8].

• In 2006, Tuncer et al. compiled multi-center data in retrospect and analyzed the origin and distribution of LAD anomalies in 70,850 patients. They categorized their 3 patients of type IV dual LAD, under the anomalous aortic origins of coronaries with a prevalence of 0.004%. In two cases, the LAD₂ had a prepulmonary course, while one case had an intramyocardial course that was later labeled by Manchanda et al. as type V dual LAD [1, 12].

• Despite the earlier assertion of type V dual LAD in 2013 by Manchanda et al., where LAD₂ originates from the RCS and takes an aberrant trans-septal course to reach the distal AIVS, Moulton et al. have described it again in the same year [12, 13].

• The identification of an inter-arterial course of LAD₂ originating from the RCS that further expanded the numerical classification to type VI dual LAD by Maroney and Klein [14].

• A new variant of type IV dual LAD was identified by Montero-Cabezas et al., where the descending septal artery or Bonapace’s branch originates from the RCS or RCA or common ostium of the conus branch was considered to be LAD₁, while LAD₂ usually continues as a branch of the left coronary artery. They named it reverse type IV dual LAD [15].

• Moreno-Martínez et al. formulated in 2012 a newer classification based on the older classification of Spindola-Franco et al. A variant of type I dual LAD and five variants of type IV dual LAD based on minor variations of reported cases in the literature have been described in their classification. Moreno-Martínez et al. again updated their classification in 2016 by adding type V variant as defined by Montero-Cabezas et al. with 4 subgroups based on the slight variations in the origin of the descending septal artery [16, 17].

• Subban et al. (2014) and Dhanse et al. (2018) identified a dual LAD form VII where LAD₁ originates from the LMCA earlier, which then stems from the bifurcation of LAD₂ and left circumflex artery (LCX). Bozlar et al. identified a new form of type VII dual LAD in 2015, despite previous claims by Subban et al., where the LMCA originates from the RCS and then follows the inter-arterial malignant course [4, 18, 19].

• The classification of the dual LAD was expanded by Bozlar et al. to type IX in 2015 and later, Celik et al. identified type X dual LAD in the same year. Except for a minor variation in the origin of LAD₂ and RCA from the separate ostia in the RCS, respectively, there was not much difference between types IV and X [4, 20].

• In 2018, Al-Umairi et al. reported a type XI dual LAD variant in which LAD₁ and LAD₂ shared a common ostium with the RCA originating separately from the RCS. In 2020, Pandey et al. labeled a new variant as a type XII dual LAD with just a minor variation in the origin, where LAD₂ and LMCA shared a common ostium with the RCA, and the LMCA was further divided into the LAD₁ and the LCX [21, 22].

Older classifications: Drawbacks

Dual LAD numbers have increased up to 12 types since the initial classification by Spindola-Franco et al., as reported to date in the literature [5, 23]. Also, several overlaps of numbers of the classified dual LAD variants occurred in the literature which created more ambiguity. More controversy was created as there are several unclassified cases of dual LAD [4]. The main drawback of this numerical classification was that it does not signify a concise description of the dual LAD system. The need for transparent, uniform classification was also asserted in the letters to the editor [8, 24]. We suggested a new classification to avoid the current uncertainty of an ever-increasing number of dual LADs after rejecting the least significant variables that formed the basis of previous classifications.

Novel classification: Clustering of dual LAD systems into three common groups

Criteria for the diagnosis of dual LAD

The diagnostic criteria for dual LAD based on angiographic and autopsy findings

• Two recognizable arteries, each supplying a part of the vascular territory of the LAD, should be present [3].

• Each of which will run in AIVS for a certain length before terminating [3, 4].

• The first artery—It originates either separately from the LCS or as a branch of the LMCA and/or common LAD from the LCS or anomalous origin from the RCS or RCA, which primarily courses and terminates in the proximal AIVS. It should be designated as LAD₁ (short LAD), irrespective of its place of origin, length, and branching pattern [4, 5].

• The second artery—It originates either separately from the LCS or as a branch of LMCA and/or common LAD from the LCS or anomalous origin from the RCS or RCA, which proximally travels outside the AIVS and always terminates in the distal AIVS. It should be designated as LAD₂ (long LAD) irrespective of its origin, duration, and branching pattern [7, 25].

Description and method of classification

A novel classification in which dual LADs can be clustered into each of the three groups based on their morphological characteristics such as origin, course, and patterns of distribution is shown in Fig. 3. The characterization of dual LADs into groups and subgroups is based upon their usual features, the course of LAD₁ and LAD₂, and variable features as follows:

1. Group: The origin of the two components of the dual LAD (LAD₁ and LAD₂) either completely from the LCS (group I) or partly from the LCS and RCS (group II) or entirely from the RCS (group III) which are the usual [constant] features should be used to assign the dual LAD to one of the three groups.

2. Subgroups: The course of one or both of the LADs should be used to subclassify the dual LAD which has therapeutic and prognostic implications [26].

3. Variable features: There are minor morphological variations in patterns of distribution in each category, which should be defined after the categorization of dual LADs into groups and subgroups. Older classifications have used these variable features to categorize dual LAD into separate numerical classes or unclassified variants (Fig. 4).

Fig. 3.

Flow diagram showing the scheme of a novel classification of dual LAD. The diagnosis of dual LAD is based on angiographic or autopsy findings of 2 arteries that supply the same vascular territory. Based on the origins of the LAD₁ and LAD₂ either completely from the LCS and RCS or exclusively from the RCS, dual LAD is categorized into one of the three groups. It is further subgrouped based upon their four courses: epicardial or prepulmonic or anterior (A); inter-arterial or between (B); retro-aortic or posterior (P); intra-myocardial or septal (S). LAD, left anterior descending artery; LCS, left coronary sinus; RCS, right coronary sinus

Fig. 4.

Variable features of three groups of novel classification. Upper panel (group I): the absence of the LMCA and common LAD and separate origin of LAD₁ and LAD₂ form LCS (Ia), the early origin of LAD₁ from the LMCA which bifurcates into LAD₂ and LCX (Ib), the separate origin of LAD₁ from LCS (Ic), equal lengths of LAD₁ and LAD₂ (Id), reverse lengths of LAD₁ and LAD₂ (Ie), epicardial right ventricular course of LAD₂ (If), epicardial left ventricular course of LAD₂ (Ig), triple LAD anomaly wherein the inferior ventricular artery enters AIVS (Ih). Middle panel (group II): the absence of the LMCA (IIa), the separate origin of LAD₁ and LCX (IIb), equal lengths of LAD₁ and LAD₂ (IIC), reverse lengths of LAD₁ and LAD₂ (IId), the separate origin of RCA and LAD₂ from RCS (IIe), the origin of LAD₂ from the proximal segment of the RCA (IIf) and the mid-segment of the RCA (IIg), anomalous origin of the LCX from the RCS/RCS (IIh). Lower panel (group III): the origin of LAD₁ and LAD₂ from the RCS both of which courses epicardially, anterior to the right ventricular outflow tract (prepulmonic) and then follows the distribution like group I (IIIa), the common origin of LAD₂ and LMCA from the RCS wherein LMCA divides into LAD₁ and LCX which takes retro-aortic course (IIIb), separate origins of LAD₂ and LMCA from the RCS wherein LMCA divides into LAD₁ and LCX which takes retro-aortic course (IIIc), the origin of the LAD₂ from the proximal segment of RCA while LMCA, LAD₁, and LCX follow a similar course as in IIIb (IIId), the origin of the LAD₂ from the proximal segment of RCA, LAD₁ from the RCS while the normal course of the LCX from the LCS (IIIe), absence of LMCA and separate origin of LAD₁ and LAD₂ from the RCS while the normal course of the LCX from the LCS (IIIf), inter-arterial course of the LAD₂ (IIIg), intramyocardial course of the LAD₂ (IIIh)

Group I or “split” dual LAD system

Usual features

1. The entire left coronary artery and its major branches arise from the LCS.

2. Typically, the LMCA divides into the LAD and the LCX.

3. The proper or common LAD bifurcates into LAD₁ and LAD_2.

4. LAD₁: terminates in the proximal AIVS and predominantly gives rise to septal branches.

5. LAD₂: traverses epicardially with deviated course either on the LV or RV side or intramyocardially to re-enter into the distal AIVS that terminates either at the apex or may continue beyond the apex [3–5].

Subgroups

Group I was further divided into three subgroups depending on a single clinically relevant variable like the course of the LAD₂ as follows:

• i.Anterior or epicardial [A]
• ii.Septal or intramyocardial [S]
• iii.Combined

Variable features

1. Early or separate origin of the LAD₁ from the LMCA or the LCS [19, 27, 28].

2. Absence of the common LAD—separate origin of the LAD₁ and LAD₂ from the LMCA (illustrated case 1: Fig. 1a–d) [29].

3. Epicardial LV or RV course of the LAD₂ [4, 5].

4. Equal or reverse lengths of the LAD₁ and LAD₂ [30].

5. Branching pattern—a trifurcation lesion involving a large diagonal branch, the LAD₁, and LAD₂ [31].

6. Associated coronary anomalies—triple LAD anomaly, hyperdominant LAD, and congenital absence of the LCX [4, 9, 32, 33].

Group II or “true” dual LAD system

Usual features

• The left coronary artery originates partially from the LCS and RCS.

• Usually, the LMCA divides into the LAD₁ and the LCX.

• LAD₁: can be called a left-sided LAD that terminates in the proximal AIVS. This course is relatively unaltered.

• LAD₂: can be called a right-sided LAD that originates from the RCS or any segment of the RCA. Typically, the proximal segment of the LAD₂ follows a variable path while its distal segment has a constant course that re-enters in the distal AIVS to terminate into the LV apex [34].

Subgroups

Group II was further divided into five subgroups depending on a single clinically relevant variable like the course of the LAD₂ as follows:

• i.Anterior free wall or prepulmonic [A]
• ii.Inter-arterial [B] (illustrated case 2: Fig. 5a–c)
• iii.Posterior or retro-aortic [P]
• iv.Septal or intramyocardial [S]
• v.Combined

Fig. 5.

a-c: Multi-detector computed tomography coronary angiography of Group II dual LAD (case 2). It revealed a separate origin form the RCS (black arrow) and malignant inter-arterial course (between the right ventricular outflow tract and aorta) of the LAD₂ (maximum intensity projection view, a) origin from volume rendered images (b, c) confirmed the findings of conventional angiography which demonstrated LAD₁ (dashed arrow) and LAD₂ (solid arrows). As per the novel classification, we categorized a group, II-B dual LAD. LAD, left anterior descending artery; RCS, right coronary sinus

Variable features

1. Absence of the LMCA and separate origin of the LAD₁ and the LCX from the LCS [12, 13].

2. The separate or common origin of the LAD₂ from either the RCS or the proximal or mid-segment of the RCA [20, 35–37].

3. Equal or reverse lengths of the LAD₁ and LAD₂ [34, 38].

4. Branching pattern—after entering the superior aspect of the AIVS, the LAD₂ provides a small septal perforator or the LAD₁ gives off a large diagonal branch [13, 39].

5. Associated coronary anomalies—anomalous origin of the LCX from the RCS or intercoronary communication [40–46].

Group III or “anomalous” dual LAD system

Usual feature

The entire left coronary system arises from the RCS and lacks a constant morphological feature.

Subgroups

Group III was further divided into five subgroups depending on a single clinically relevant variable like the course of the LMCA, LAD₁, and LAD₂ as follows:

• i.Anterior free wall or prepulmonic [A]
• ii.Inter-arterial [B]
• iii.Posterior or retro-aortic [P]
• iv.Septal or intramyocardial [S]
• v.Combined

Variable features

There are several variables with either combined or separate origins of LMCA, LAD₁, and LAD₂ from either the RCS or RCA contributing to various combinations as follows:

1. Origin of the LMCA: Separately from the RCS or common ostium with the RCA or the proximal segment of the RCA [43, 47].

   1. The LMCA bifurcates into the LAD₁ and LAD₂ and each of which traverses to the left side to reach the AIVS and follows a pattern of distribution like the group I dual LAD [4, 48].
   2. The LMCA bifurcates into the LAD₁ and the LCX which traverses to the left side and LAD₁ terminates in the proximal AIVS. There is a separate origin of the LAD₂ from the RCS or the RCA which supplies the mid and distal AIVS. It follows the pattern of distribution like group II dual LAD [49, 50].
   3. The absence of the LMCA and the separate origins of the LAD₁ and LAD₂ from either the RCS or the RCA [21].

2. Equal or reverse lengths of the LAD₁ and LAD₂—not reported in the literature.

3. Branching pattern—LAD₁ supplies all the septal and diagonal branches [47].

4. Associated coronary anomalies—the joint origin of the LMCA and the RCA (single coronary artery pattern) from the RCS is categorized as the anomalous coronary artery origin from the opposite sinus (ACAOS) [7, 51].

Method of classification

Due to the omniplanar ability of multi-detector computed tomography (MDCT) to understand the exact course of the anomalous coronary arteries, MDCT is recommended to be performed in addition to conventional angiography while classifying dual LAD as described below [26, 52].

• One of the three groups is assigned to the dual LAD, as described in the usual features, following confirmation of the diagnosis.

• The variable course of the proximal segment of the LAD₂ is defined using a single alphabet to allocate the subgroup where the LAD₁ follows a usual course, e.g., group I-A, group II-S, group III-B (Fig. 6).

• Use two alphabets to assign the combined subgroup if the proximal segments of both the LADs have a different course. The first alphabet refers to the course of the LAD₁ while the second alphabet refers to that of the LAD₂, e.g., group I-SA, group II-SB, group III-AP.

• The variable feature of the dual LAD to be described after assigning to one of the three groups and corresponding subgroup as described below, e.g.

  • Group I-A: Separate origin of LAD₁ and LAD₂ from the LMCA and absence of the common LAD with hyperdominant LAD₂ (illustrated case 1: Fig. 1a–d).
  • Group II-B: Inter-arterial course of LAD₂ (illustrated case 2: Figs. 2a–d and 5a–c).
  • Group III-SA: Intramyocardial course of LAD₁ and prepulmonic course of LAD_2.

Fig. 6.

Schematic representation of the novel classification. Depending upon the origins of LAD₁ and LAD₂ either from the LCS, LCS/RCS, and RCS, a dual LAD anomaly is divided into three groups. Furthermore, the course of the LAD₂ is either epicardial or prepulmonic or anterior (A); inter-arterial or between (B); retro-aortic or posterior (P); intra-myocardial or septal (S). CA, coronary arteries; LAD, left anterior descending artery; LMCA, left main coronary artery; Cx, circumflex artery; RCA, right coronary artery; IVS, interventricular septum; LCS, left coronary sinus; RCS, right coronary sinus

Conclusion

A novel classification of dual LAD is proposed where it follows the three common patterns of distribution. Each case of dual LAD should be placed in one of these three groups, additional subgroups, and variable features to be meaningfully defined. This will create uniformity in the identification and diagnosis of the dual LAD system. Our novel classification carries therapeutic implications as it helps to divide into benign or malignant types based on the original classification of a single coronary artery. Since the LAD is by far the most critical coronary artery, clinicians and diagnosticians need to be aware of the possibility of a dual LAD to prevent the misinterpretation of coronary angiography and to facilitate effective myocardial revascularization.

Author contributions

All the authors contributed to conceptualization, data curation, formal analysis, investigation, methodology, software, supervision, validation, roles/writing—original draft, and writing—review and editing.

Funding

There is no source of funding for this article.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Informed consent

Informed consent was obtained from a participant included in the study.