Review Article

Idiopathic Annular Ventricular Arrhythmias

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Abstract

Idiopathic arrhythmias originating from the mitral and tricuspid annuli are commonly encountered in clinical practice. This review focuses on distinguishing features of ventricular arrhythmias arising from these structures and the importance of distinguishing idiopathic arrhythmias from those associated with structural heart disease. Each region along the mitral and tricuspid annuli (including the cardiac crux and para-Hisian region) is then discussed separately, with a particular emphasis on the ablation strategies and pitfalls for each. Although this review series is centred around idiopathic ventricular arrhythmias, the strategies for ablation techniques in these regions are broadly applicable.

Keywords

Catheter ablation, ventricular arrhythmias, idiopathic arrhythmias, mitral annulus, tricuspid annulus,

Disclosure:WGS has received grants from the American Heart Association, National Institutes of Health and Varian Health Systems; royalties from Elsevier; honoraria from Abbott, Biotronik, Boston Scientific, Johnson & Johnson, Mediasphere and Medtronic; and travel support from the Japanese Heart Rhythm Society; and is on the editorial board of Arrhythmia & Electrophysiology Review; this did not affect peer review. ZTY has no conflicts of interest to declare.

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Accepted:

Published online:

DOI:https://doi.org/10.15420/aer.2024.40

Correspondence Details:William G Stevenson, Professor of Medicine, Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Medical Center East, 5th Floor, 1215 21st Avenue South, Nashville, TN 37232, US. E: william.g.stevenson@vumc.org

Open Access:

This work is open access under the CC-BY-NC 4.0 License which allows users to copy, redistribute and make derivative works for non-commercial purposes, provided the original work is cited correctly.

Ventricular arrhythmias arising from the mitral and tricuspid annuli are commonly encountered in clinical electrophysiology. Sometimes referred to as ‘inflow tract’ arrhythmias, in contrast to outflow tract arrhythmias, they occur in a spectrum of diseases and may be benign and idiopathic in those without identifiable structural heart disease or manifestations of underlying severe cardiomyopathy. With improvements in technology, most of these arrhythmias can be effectively treated with ablation.1,2 Although this review focuses on the idiopathic arrhythmias, the ablation strategies described are also applicable to arrhythmias arising from these important clinical regions in patients with structural heart disease.

Incidence and Mechanism

Idiopathic arrhythmias arise from annular structures in 5–10% of patients referred for ablation of idiopathic ventricular arrhythmias.3 In cohort studies of idiopathic ventricular arrhythmias, sites of origin from the tricuspid and mitral annulus are relatively uncommon compared with the outflow tracts, papillary muscles and fascicular system.2,4 Because the valve annulus is a common origin for idiopathic focal tachycardias arising in both the ventricle and atrium, a common developmental origin for these arrhythmias has been suggested.5 The sustained ventricular arrhythmias usually have a focal origin, are often catecholamine sensitive and some can be terminated with a Valsalva manoeuvre, adenosine and/or verapamil, suggesting triggered automaticity as a potential mechanism.6

Recent studies of genetic cardiomyopathies, including those related to lamin A/C (LMNA), titin (TTN) and desmoplakin (DSP) gene variants, have demonstrated a propensity for fibrosis to develop at the base of the heart.7−9 Annular ventricular arrhythmias can potentially be an early manifestation of disease. Because this distinction carries prognostic implications for both procedural planning and long-term follow-up and prognosis, a thorough cardiac evaluation is important.10

Evaluation of Patients With Annular Arrhythmias

The likelihood that premature ventricular contractions (PVCs) or ventricular tachycardia (VT) originate near the valve annulus is often initially recognised based on the QRS morphology of the arrhythmia and is reviewed in detail for specific locations below. Although idiopathic annular ventricular arrhythmias cannot be distinguished from those arising from structural heart disease by ECG alone, there are features of the ECG that may provide some insight.11 The presence of conduction system abnormalities always raises the suspicion for structural heart disease.12 In a patient with otherwise unexplained conduction system abnormalities, the presence of annular ventricular arrhythmias arising from a location remote from the septum may signify a more diffuse ventricular scar than previously recognised. Along similar lines, the presence of more than one ventricular arrhythmia, especially if arising from remote locations, may reflect extensive or diffuse disease. Fractionation of the sinus rhythm QRS suggests an underlying myopathic process, although is not definitive.13–16

A careful history and physical examination may reveal other signs of incipient cardiomyopathy. Syncope can be a feature of idiopathic ventricular arrhythmias, but should increase the suspicion for underlying heart disease and warrants careful investigation for underlying cardiomyopathy.17 Prior history of chest pain and heart failure symptoms are worrying features of potential underlying structural heart disease. A careful family history is important, including identifying relatives who had sudden death, cardiomyopathy or prior defibrillator implantation, which may indicate a genetic cardiomyopathy or arrhythmic disorder. In addition, miscarriages and accidental or traumatic deaths in the family may be sudden deaths.18,19 Finally, the presence of AF along with annular ventricular arrhythmias may be further evidence of an underlying myopathic process, especially in younger patients.20

Thorough evaluation of patients with annular ventricular arrhythmias for underlying structural heart disease is highly recommended. Cardiac imaging to assess left ventricular (LV) and right ventricular (RV) size and function is warranted. In patients with myopathic processes, cardiac MRI may show areas of delayed gadolinium enhancement consistent with scar, although small scars and scars along an annulus may escape detection.

At the time of electrophysiological study, further evidence of underlying structural heart disease should be carefully considered. The majority of idiopathic ventricular arrhythmias are catecholamine sensitive, consistent with foci of triggered activity or enhanced automaticity.21,22 Re-entrant arrhythmias in the absence of structural heart disease are rare, although they have been reported.23 Some of these arrhythmias involve the fascicular Purkinje conduction system and are discussed elsewhere.24,25 More commonly re-entrant arrhythmias are associated with myocardial scar. The presence of a re-entrant ventricular arrhythmia or more than one QRS morphology of ventricular arrhythmia strongly suggests an underlying myopathic process.26 Similarly, the finding of low-voltage regions and abnormal electrograms consistent with regions of ventricular scar within the basal region of the heart are common in many cardiomyopathies.27,28

General Strategies for Focal Arrhythmias

Because the majority of idiopathic ventricular arrhythmias are focal, the principles and strategies for ablation are similar to those used for all focal arrhythmias.29,30 The QRS morphology of the arrhythmia gives insight as to the likely site of origin for a focal arrhythmia.31 The suggested origin can help guide the vascular access and approach to the rest of the mapping and ablation. Particularly for PVCs, it is important to obtain a 12-lead ECG of the arrhythmia prior to implementation of sedation or anaesthesia that may suppress the arrhythmia.

Once the general region has been located, two primary methods are used to identify the site of origin: activation mapping and pace mapping.31 The two methods are complementary, although activation mapping is more accurate. The goal of activation mapping is to identify the earliest site of activation. Computerised electroanatomical mapping systems have automated and accelerated this process, but can make errors, and it is important to evaluate the electrograms carefully in the region of interest.32 Simultaneously recording both bipolar and unipolar signals from the mapping catheter can be helpful.33 At successful ablation sites, a closely spaced bipolar electrogram usually shows a signal approximately 20–30 ms prior to the QRS onset.34 Care must be taken that the bipolar signal represents a true myocardial potential, because mapping along valve annuli signals can be an artefact from leaflet or chordal interaction with the catheter or adjacent atrial electrograms. Concomitant with the bipolar signal, a unipolar signal from the distal pole of the mapping catheter will usually demonstrate a QS pattern consistent with a wave front of activation uniformly moving away from the potential site of origin. However, if the unipolar signal is an rS pattern, there is yet more myocardium between the site of origin and the location of the catheter, although this does not preclude successful ablation because the origin may still be within reach of ablation heating. The onset of the unipolar electrogram should coincide with the onset or first peak of the bipolar electrogram. If the local electrogram does not precede the QRS, the chance of success with ablation is low.35

Due to infrequent ventricular arrhythmias, especially under sedation, activation mapping is sometimes not possible. In these cases, and to complement activation mapping, pace mapping is useful. The method of pace mapping for annular arrhythmias is the same as that described for other idiopathic ventricular arrhythmias.36 Pacing at the site of origin of the QRS should be identical to that of the arrhythmia. Ideally the minimum pacing output should be used to capture the minimum amount of myocardium to increase the precision of this manoeuvre, but determining the pacing threshold is not usually practical at each site and we commonly start with pacing at 10 mA, 2 ms pulse width. Although unipolar pacing would theoretically have better resolution, bipolar pacing from closely spaced electrodes is more commonly used.37 The QRS should be an exact match in all 12 leads and with identical notching to the paced QRS. Electroanatomical mapping systems incorporate software that can quantitate the agreement of the paced QRS with the arrhythmia, but can be misled by artefact from pacing stimuli and by ECG leads that are low amplitude.32 Spatial resolution of pace mapping alone is limited compared with activation mapping and a similar QRS can occur over a relatively large area, including sites where ablation is ineffective.36 For some foci, pace mapping identifies an exit region that is remote from the focus. In the case of mid-myocardial or deep sites of origin, the site of successful ablation may be in a different location from the exit site, because the electrical wave front may be concealed passing through tissue prior to producing a QRS.38

Specific Annular Ventricular Arrhythmia Localisation

Mitral Annulus

The mitral annulus is a relatively large structure, encompassing the majority of the basal portion of the LV. In studies of patients undergoing ablation for idiopathic ventricular arrhythmias, an origin from the anterior portion of the mitral annulus appears to be roughly three times as common as a site of origin from the posterior inferior portions of the annulus.39 Both epicardial and endocardial sites of origin occur, with epicardial PVCs generally demonstrating a wider QRS than endocardial origins. These arrhythmias must be distinguished from origins in the papillary muscles and the fascicles of the Purkinje system. A QRS duration <130 ms excludes a mitral annular site of origin and favours a Purkinje system origin.39 In the surface ECG, septal origin arrhythmias can have a right bundle branch block (RBBB)-like configuration (dominant R wave in V1) or a left bundle (dominant S wave in V1) or Qr in V1. At non-septal sites, the arrhythmias have a RBBB-like configuration in V1 with a dominant R wave. The frontal plane axis further suggests the location, with those from the superior part of the annulus having an inferiorly directed frontal plane axis and those from the inferior annulus having a superiorly directed frontal plane axis. Most display positive precordial concordance, but can have an Rs in V5 and V6. Septal origin mitral annular arrhythmias can have a transition from dominant S in V1 to dominant R at V2 (Figure 1).39–41

Figure 1: Twelve-lead ECG Morphologies of Idiopathic Annular Premature Ventricular Contractions

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Figure 1: (Continued)

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Following analysis of QRS morphology, initial mapping of the perimitral annulus can be performed, assessing far-field ventricular signals from the coronary sinus and great cardiac vein (GCV) as it courses along the mitral valve. This usually allows rapid localisation of the arrhythmia.

Arrhythmias arising from the mitral valve annulus are potentially amenable to ablation either from a transeptal or a retrograde approach.42 Success rates vary, but are reported as high as approximately 80%.42 PVCs arising from the mitral annulus often arise from or in very close proximity to the valve ring itself, and both an atrial and ventricular electrogram are often present at the successful ablation site.43 Electrogram interpretation is complicated by the presence of an atrial signal, as well as possible artefact from valve motion. It is critical to ensure the ablation catheter is directly opposed to the valve ring and not against the valve leaflet. In most cases this requires the use of the catheter inversion technique, forming a looped catheter within the LV cavity, which is then withdrawn to the valve annulus.44 In making this loop from a transeptal approach, care must be taken to avoid exerting excessive force against the free wall of the LV. Pacing from the ablation electrode should demonstrate capture if the electrode is in contact with the ventricular myocardium. When the catheter is wedged in trabeculae underneath the mitral annulus, steam pops and ventricular perforation are risks if heating is excessive. Careful titration of power based on impedance fall and intracardiac ultrasound imaging is a reasonable approach.45

Free Wall Mitral Annular Arrhythmias

The lateral mitral annulus is a relatively uncommon location for idiopathic PVCs. The papillary muscles and chordae can be obstacles to orienting the loop of the catheter to reach this location from a transeptal approach. A retrograde aortic approach can be easier. Epicardial ablation is a consideration when endocardial ablation fails, but is often limited by epicardial fat in the atrioventricular (AV) groove that limits effective ablation, and by the epicardial coronary arteries that must be avoided. Coronary venous ethanol ablation has been used for PVCs arising from this region. However, the coronary venous anatomy can be limiting.46

Aorto-mitral Continuity and Superior Mitral Annulus

The aorto-mitral continuity (AMC) is a fibrous trigone connecting the aortic and mitral valve rings and is bounded by several cardiac structures, including the left coronary cusp and aorta, the mitral annulus and LV myocardium.47 In a study of patients referred for idiopathic PVC ablation, the myocardium adjacent to the AMC was found as the site of origin in 8.8%.47 On surface electrogram, AMC PVCs may be either RBBB or left bundle branch block (LBBB) configuration in V1, with inferior axis and typically a prominent S wave in V2.47 Ventricular mapping has identified a sharp potential prior to the QRS in this region, suggesting that conduction tissue remnants may run within this area and be the source of origin for some ventricular arrhythmias.48

Ventricular arrhythmias arising from the AMC are amenable to ablation. A retrograde aortic approach allows for easy access to the area below and above the aortic valve. However, the AMC region below the valve is also reachable with a transeptal approach by prolapsing the catheter similar to the approach described above for the mitral annulus; however, the curve necessarily tends to be tighter. Ablation from the left coronary sinus of Valsalva, endocardial LV or GCV are all options to consider. Lesions in the left sinus of Valsalva directed towards the AMC are successful for some, but care must be taken to avoid the left main coronary artery. An intracardiac echocardiogram may be helpful.

The site of origin for PVCs arising from the anterior mitral annulus may be deep within the myocardium or epicardial. The finding of a simultaneously early GCV and LV endocardial site or a GCV site earlier than the earliest LV site may be a clue. Endocardial ablation adjacent to the early epicardial activation site, described as the anatomical approach, can be successful.49,50 This approach can also be used when ablation at the earliest endocardial site fails. Long radiofrequency applications of 2–4 min with careful power titration based on impedance falls may enhance lesion depth for suspected deep intramural foci (Figure 2).

Figure 2: Anatomical Ablation of a Mitral Annular Premature Ventricular Contraction

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Ablation from within the GCV can be successful but is often limited by venous anatomy and limited energy delivery. Coronary angiography is required to assess the potential for damage to adjacent coronary arteries, and maintaining a distance of 4–5 mm or more between the coronary artery and the ablation catheter is prudent.51 Ablation energy delivery is limited by low blood flow and high impedance.40,52 The use of half normal saline irrigation may improve energy delivery.53 Bipolar ablation between the GCV and LV endocardium or left sinus of Valsalva has also been reported.54,55

Basal Left Ventricular Septum and Peri-His

The septum can be a source of idiopathic ventricular arrhythmias, although arrhythmias in this area are often associated with structural heart disease. The basal septum away from the membranous portion is thick. In an early case series of patients undergoing ablation for ventricular arrhythmias without recognised heart disease, 8% originated from within the septum.56 A recent study reported that only 2% of idiopathic ventricular arrhythmias had an inferobasal septum origin.57 This discrepancy is likely explained by a more complete realisation of incipient underlying myocardial processes in those patients previously deemed as idiopathic. Cardiac MRI of patients with ‘idiopathic’ ventricular arrhythmias, especially arising from the basal septum, uncovered late gadolinium enhancement or signs of fibrosis in a proportion of these patients.58 Unsurprisingly, the presence of concealed fibrosis in the basal septum predicted recurrence of ventricular arrhythmias after ablation. In patients with ventricular arrhythmias originating from the basal intraventricular septum, careful evaluation for underlying structural heart disease should be considered, especially if coexisting with other signs of septal fibrosis (i.e. conduction disease).

Ventricular arrhythmias arising from the basal inferior LV septum typically have a left superior axis with lead II less negative than lead III. The pattern may be either right bundle in morphology or left bundle with a ‘reverse pattern break’ in V2 with a prominent R wave.57 As the point of origin moves more superiorly along the septum, the axis remains leftward but shifts more inferiorly. At sites approaching the left bundle and left-sided His bundle region, the QRS is narrower.

The approach for the ablation of foci within the basal septum is similar to that of the approach to septal ventricular arrhythmias arising in structural heart disease.59,60 Ablation from both sides of the intraventricular septum may be required to reach a deep septal focus. Small-diameter mapping catheters able to cannulate septal venous perforating veins from the GCV can be helpful in identifying mid-mural points of origin.61 These small perforating septal branches can also be potentially used for ethanol ablation. However, in idiopathic arrhythmias, this less targeted approach risks the development of bundle branch block or AV block.60

Cardiac Crux

The cardiac ‘crux’ refers to an inferior region of the heart where many of the heart structures come together. Located at junction of the right atrium, left atrium, inferior basal portion of the RV and LV, this pyramidal region is composed of epicardial fat and the epicardial vessels on its epicardial borders. Within this region, the middle cardiac vein splits from the coronary sinus in this location and runs in the intraventricular groove on the inferior aspect of the heart. The posterior descending artery also arises from this location, typically from the right coronary artery. Ventricular arrhythmias that arise from this region were described in 2009 in four patients out of 340 referred for catheter ablation for idiopathic ventricular arrhythmias.62 Compared with idiopathic ventricular arrhythmias from other sources, syncope is relatively common as a presentation, and sudden cardiac death requiring resuscitation has been reported.63 Crux ventricular arrhythmias have been further subdivided into apical crux and basal crux.63 In the surface electrogram, crux ventricular arrhythmias have a left superior axis, with the majority of patients having an abrupt V2 transition.1 The apical versus basal crux locations were distinguished by the LBBB versus RBBB pattern in V1 and the R versus S pattern in V6. Apical crux VT patients were noted to have an RBBB pattern with S greater than R in V6. In contrast, basal crux VT patients were noted to have an LBBB pattern with more prominent R waves in V6. In contrast with idiopathic ventricular arrhythmias arising from other annular structures, VT is relatively more common for arrhythmias arising from the cardiac crux. This VT is often catecholamine sensitive.

Strategies for treating crux ventricular arrhythmias involve ablation from within the middle cardiac vein for basal crux VT or from within the pericardial space after epicardial access for more apical crux VT (Figure 3). Due to the proximity of the posterior descending artery, coronary angiography is required in this location. In the largest series reported, success rates for the basal crux acutely were as high as 94% with ablation within the middle cardiac vein or coronary sinus, with recurrence rate of 6%.64 Success rates for apical crux VT are considerably lower, at only 14% despite epicardial mapping and ablation.65

Figure 3: Basal Cardiac Crux

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Posterior–superior Process

The posterior–superior process (PSP) of the LV is the most posterior and superior (dorsal) structure of the LV.66 Ventricular arrhythmias arising from the PSP are relatively uncommon and were first reported in 2016.67 Similar to the para-Hisian region, the PSP is primarily of interest due to the proximity of other structures. The ECGs of these arrhythmias may show right or left bundle morphology and the frontal plane axis can be inferior, superior or in between.67

Unique among the idiopathic ventricular arrhythmias, ventricular arrhythmias arising from the PSP can be ablated successfully from the right atrium.67 Consequently, the AV node can be a risk. Ablation from within the LV can also be successful, but does not negate the risk entirely.68 AV nodal conduction should be monitored closely during ablations in this region.

Tricuspid Annulus

Idiopathic ventricular arrhythmias arising from the tricuspid valve annulus are rare. Similar to the mitral valve, the majority arise from the superior (anterior) aspect of the annulus. The QRS morphology shows a left bundle-like pattern with a dominant S wave in V1 and a leftward frontal plane axis with dominant R in lead I. Other features depend on the precise location.69

Similar to the mitral valve, achieving ablation of ventricular arrhythmias from the tricuspid valve annulus requires ensuring that a valve leaflet is not interfering with tissue contact. However, the tricuspid valve is more mobile than the mitral valve apparatus, which may make achieving stability in this region challenging. The lateral tricuspid valve is particularly mobile. Elimination of ventricular arrhythmias arising from the tricuspid valve annulus on the free wall often requires the inverted catheter technique described above for the mitral apparatus.70 Care must be taken to avoid excessive forces on the catheter in this orientation due to the risk of perforation. Access from the internal jugular vein into the RV may assist with the angle of approach.

Para-Hisian Region

The para-Hisian region is the area in proximity to the proximal conduction system, which, on the RV side, is a region of the septal aspect of the tricuspid valve annulus/RV inflow tract near the membranous portion of the ventricular septum adjacent to the His bundle.71 Para-Hisian PVCs typically have a relatively narrow left bundle QRS. Lead II is positive, but the frontal plane axis can be inferior, horizontal or superior leftward such that lead III can be positive or negative in polarity.72 The precordial transition can be after V3.73 Although near the conduction system, ventricular arrhythmias from this location do not generally involve the conduction system directly. Rather, it is the proximity to the conduction system and the potential for collateral damage from ablation that lead to the unique characterisation. Due to the high degree of concern for conduction system damage, a thorough risk–benefit discussion with the patient is necessary prior to proceeding with ablation for ventricular arrhythmias arising near the His bundle.

Para-Hisian PVCs are considered higher risk primarily due to the risk of damage to the conduction system. However, ablation can often be achieved without AV block.74,75 Although a His potential may be recorded at the initially detected early site, in fact the focus may be removed from the true region of concern either inferior or superior to the His bundle, which may be determined by more detailed mapping. Pacing manoeuvres have been used to identify a safe distance between His capture and earliest activation.76

When the site of origin is found to be close to the His bundle, additional strategies can be considered. The first is mapping within the aorta in the right and non-coronary cusp.77,78 Successful ablation may be achieved at this site with a lower risk of heart block. For ablation in close proximity to the conduction system, cryoablation can be considered.79 The primary advantage of this approach is widening the window of safety between the time that cooling of the conduction system is observed and the production of permanent damage. However, even with this approach, permanent AV block has been reported.79 In rare cases, the site of origin for the ventricular arrhythmias may remain close enough to the His bundle that elimination of the arrhythmia obligates heart block and pacemaker implantation. A careful risk–benefit discussion with the patient is crucial.

Conclusion

Although relatively uncommon among idiopathic ventricular arrhythmias, annular ventricular arrhythmias are an important clinical entity. Arrhythmias associated with cardiomyopathies often arise in these locations and careful assessment for structural heart disease is an important consideration. The approach, risks and efficacy of ablation are importantly influenced by the location of the origin of the arrhythmia, which can be anticipated from the ECG.

Clinical Perspective

  • Idiopathic ventricular arrhythmias arising from the mitral and tricuspid annuli are less common than those from the outflow tracts, but more common in structural heart disease.
  • These regions are amenable to ablation, with high success rates for idiopathic arrhythmias.
  • Strategies and pitfalls for ablation in each annular region are broadly applicable to arrhythmias arising in structural heart disease as well as idiopathic arrhythmias.

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