The challenging nature of chronically occluded coronary artery recanalization is driving the development of novel procedural techniques such as HydroDynamic contrast recanalization (HDR), an antegrade chronic total occlusion (CTO) crossing strategy derived from the Carlino technique involving intraplaque injection of a small volume of contrast beyond the boundary of the proximal cap, followed by polymer-jacketed wire use. Results of a retrospective case series study by Mauro Carlino et al. in September 2024 highlighted its efficacy in patients with favourable CTO anatomy [1].
We provide a step-by-step outline of the HDR technique using a case study of a 74-year-old female smoker, with arterial hypertension, symptoms of Canadian Cardiovascular Society (CCS) grade II angina, upper and lower extremity arterial disease and colon cancer. Her resting echocardiogram showed left ventricular ejection fraction of 60%, with no evidence of regional abnormalities. A single left radial access was obtained due to right radial occlusion and severe bilateral iliac disease. Furthermore, we discovered left ostial subclavian artery occlusion, which was subsequently opened with balloon angioplasty to gain access to the ascending aorta (Figures 1 A, B). Coronary angiography showed significant proximal left anterior descending artery (LAD) stenosis (Figure 1 C) and proximal right coronary artery (RCA) occlusion with J-CTO score = 2 and CASTLE score = 2 (Figures 2 A, B).
Figure 1
Left subclavian artery recanalization and percutaneous coronary intervention (PCI) of left main (LM) and left anterior descending artery (LAD). A – ostial left subclavian artery (LSA) occlusion (white star); B – post-angioplasty angiogram showing LSA opened with 6.0/15 mm balloon; C – significant stenosis of the ostium and proximal segment of LAD (black curved arrow), D – numerous tortuous septal collateral connections CC1 (Werner’s classification) to the posterior descending artery, potentially suitable for retrograde approach (black stars); E, F – DES Ultimaster Nagomi 3.0/33 mm implantation in LM and LAD (white curved arrow); G, H – IVUS measurement after stent implantation: LM minimal stent area of 12.3 mm2, LAD minimal stent area of 6.7 mm2
The first part of the procedure involved percutaneous coronary intervention (PCI) on the left main (LM) and LAD with DES implantation (Figures 1 E, F), and intravascular ultrasound (IVUS) imaging confirming the optimal result (Figures 1 G, H). Then the RCA was intubated with a JR 4.0 6F guiding catheter with side holes due to severe pressure dumping when the AL 7F was used. We applied the reference images of the distal RCA from the left coronary injection.
We advanced a Finecross M3 microcatheter (MC) over Sion Blue work-horse wire to the proximal cap. More penetrable coiled MCs should be used in cases of severe calcifications.
Proximal cap was easily punctured with the Fielder XTA guidewire. In cases of resistance, medium- (Gaia family) or high-penetration force wires (CP12, Hornet 14, or Infiltrac) are recommended. The wire should penetrate the body of the CTO by up to 3–5 mm to minimise the possibility of entering the extraplaque space. Then the MC was advanced over the wire up to its tip beyond the proximal cap boundary (Figure 2 C).
In the next step, after filling the microcatheter with pure contrast and ensuring that it was free of air, a small amount (0.5 ml) of contrast was very slowly (1 min) injected using a 2 ml Luer-lock syringe under cineangiography, until it appeared within the CTO body distal to the MC tip (Figure 2 D).
The contrast syringe was removed, and a Gladius EX guidewire was inserted into the microcatheter. Low-penetration polymeric wires (Fielder family, Fighter), straight or with a short tip bend (< 2 mm and ~30° angle), could be used alternatively at this stage. If the wire cannot be advanced further into the plaque, further injections after advancing the microcatheter by a few millimetres are recommended until the wire reaches the distal true lumen.
Figure 2
Recanalization of the right coronary artery with HydroDynamic contrast recanalization (HDR) technique. A – blunt and moderately calcified proximal cap (white arrow), chronic total occlusion (CTO) body length > 20 mm; B – non-ambiguous, blunt and moderately calcified distal cap with the bifurcation with small right ventricular branch (black arrow); C – Finecross M3 microcatheter (MC) advanced to the proximal cap, Fielder XTA guidewire penetrating up to 4 mm into the body of the CTO (white star); D – staining within the body of the CTO after slow injection of 0.5 ml of contrast identifying pattern type 2A (black arrows); E – wiring postero-lateral artery (PLA) of RCA (black star); F – contrast MC tip injection into the posterior descending artery (PDA) confirming intraluminal distal course (white curved arrow); G – IVUS-guided strategy planning after wire exchange for Sion Blue; H – RCA angiogram after DES Xience Pro 3.5/48 mm implantation, followed by post-dilatation (black curved arrow); I – optimal stent expansion in IVUS imaging
We managed to wire the distal true lumen after single intraplaque injection. The reference images, successful repeated wiring of both RCA branches, and contrast tip injection confirmed the intraluminal distal course of the wire after it crossed the occlusion site (Figures 2 E, F). Subsequently, the proximal segment of the RCA received a drug-eluting stent, with the optimal result confirmed by IVUS (Figures 2 H, I). The procedure took 90 min, we used 150 ml of contrast volume, fluoroscopy time was 33 min and the dose exposure was 752 mGy. In the event of the wire failing to enter the distal true lumen, crossing into the extraplaque space, or forming a knuckle, re-puncturing the proximal cap at a different location and repeating the HDR sequence, switching to a wire escalation or an antegrade (ADR) or retrograde (RDR) dissection re-entry strategy are the options.
Using contrast as a therapeutic tool for CTO PCI was first described by Carlino et al. in 2008 as contrast-guided subintimal tracking and re-entry (CG-STAR) [2]. The technique initially involved forceful injection of a large volume of contrast (3–5 ml) into the subintimal space to create at least one fenestration for wire re-entry into the distal true lumen. Unfortunately, this approach was associated with high restenosis rates, likely due to unpredictable and extensive vessel injury. Despite the well-established safety of contrast-based plaque modification, the Carlino technique is thought of as a “bail-out” manoeuvre in challenging anatomical subsets due to uncertainties regarding its mechanism, concerns over intraplaque contrast delivery safety, fears of vessel disruption limiting further crossing strategies, and a lack of standardisation. Furthermore, intraplaque staining following contrast delivery can be challenging to interpret and may be mistaken for a perforation. Subsequent attempts to improve the initial technique included more precise proximal cap puncturing methods to minimize entry into extraplaque spaces. Additionally, intraplaque injections using a reduced contrast volume (< 3 ml) mixed with nitroglycerine were introduced, culminating in the development of HDR [3–5].
The HDR developers postulate that intraplaque delivery of small contrast volumes can facilitate polymer-jacketed wire crossing through the recruitment of lipid-rich soft regions within the plaque, and they classify the resulting staining patterns into three distinct types based on morphology [1]:
Pattern 1: A patchy appearance with soft edges, typically forming around the microcatheter tip. The pattern is frequently observed in long occlusions (> 20 mm) and may result from contrast infiltration into soft, lipid-rich areas of the plaque.
Pattern 2: Characterised by a more defined, often linear appearance that terminates either in the distal true lumen (type 2A) or a side branch (type 2B). The pattern is related to the recruitment of multiple adjacent soft areas.
Pattern 3: Displays morphological features of types 1 and 2 and can be observed in occlusions of any length, initially appearing patchy at the origin and becoming more defined towards the distal true lumen or a side branch.
Despite the preliminary excellent results of HDR CTO PCI with a 100% success rate reported by Carlino et al., the real life experience, at least from our perspective, shows that HDR alone can serve as a final strategy in 50–60% of the cases. This success rate improves significantly when selecting patients with favourable CTO anatomy (well-defined proximal cap and distal target). Citing the founding fathers of HDR, the technique offers several advantages: a) it is simple and effective and readily applicable without requiring additional equipment, b) it is universally applicable across diverse CTO anatomies, c) it features a short learning curve, and d) it is not mutually exclusive and can complement other subsequent crossing strategies, making it suitable for a hybrid algorithm.
