Coronary angiography and angioplasty are commonly performed through the radial artery. In some patients, anatomical variations of the radial and brachial arteries, such as loops, increased tortuosity or sharp angulations may pose challenges to equipment advancement.

Both the hydrophilic guidewire 0,035'' approach and the "Serpentine" technique have been described in the literature as techniques for overcoming radial anatomical challenges, with the hydrophilic guidewire approach being the more commonly used method.

In practical terms, both techniques involve the use of the same standard materials, with differences relating mainly to operator handling and technical manipulation. This study does not introduce any experimental device, material, or treatment; instead, it aims to compare the established approach using a 0.035'' hydrophilic guidewire with the emerging " Serpentine" technique with respect to effectiveness, procedural time, and safety.

Transradial access (TRA) has become the preferred approach for diagnostic coronary angiography and percutaneous coronary intervention (PCI), compared with transfemoral access (TFA). Contemporary guidelines on revascularization in both chronic and acute coronary syndromes (ACS) recommend TRA as the first-line strategy, primarily due to its reduced risk of complications.

Additional advantages of TRA include improved cost-effectiveness, shorter intensive care unit stay, shorter overall hospitalization, faster patient mobilization, and greater patient comfort. TRA has also been associated with reduced contrast use and a lower risk of contrast-induced acute kidney injury.

Despite its advantages, TRA has limitations. It is associated with a modest increase in radiation exposure. A key drawback is the need for crossover to another access site, which is relatively common; however, this can be mitigated by operator experience and ultrasound guidance.

Anatomical variants are a major cause of procedural failure and crossover, occurring in 9-23% of patients. The most frequent variants include high origin of the radial artery from the brachial artery, arterial loops, and tortuosity of the radial or subclavian artery. Radial artery loops and severe tortuosity, observed in 4.2-13,1% of cases, are strongly associated with procedural failure (3.8-50%) and increased crossover rates. These anatomical challenges prolong procedural time, increase radiation exposure, and raise the risk of vascular complication.

Several techniques have been proposed to overcome these challenges. The most commonly adopted is the use of hydrophilic guidewires. Other techniques include mechanical straightening of tortuous segments from the operator, the use of angioplasty guidewires, microcatheters, balloon-assisted tracking (BAT), pigtail-assisted tracking (PAT), or switching to ulnar, transfemoral, or contralateral radial access.

Preservation of the transradial approach is critical, as it reduces complications, facilitates faster mobilization, and shortens hospital stay. The most common cause of TRA failure is the presence of loops and tortuosity in the radial or brachial artery. To date, no randomized trials have directly compared different strategies for overcoming these challenges. The novel "Serpentine" technique, which will be compared against the widely used "0.035" hydrophilic guidewire, could become an additional tool for interventional cardiologists-providing a reliable method for crossing loops and tortuous segments, with reduced equipment use and comparable outcomes in terms of procedure time, radiation exposure, contrast use, and local complications.

The aim of this study is to compare the efficacy and safety of the novel "Serpentine" technique with that of hydrophilic guidewires in navigating radial and brachial artery loops and tortuosity during coronary angiography and PCI via TRA.

The S-TRACK Trial will be designed as a prospective, randomized, controlled, non-inferiority study. Consecutive eligible patients undergoing coronary angiography via transradial access, and not meeting any exclusion criteria, will be screened for enrollment. After successful radial artery cannulation, patients who demonstrate resistance to guidewire or catheter advancement will undergo radial and/or brachial angiography to identify the underlying anatomical cause. Participants with angiographically confirmed anatomical variants-specifically loops, pronounced tortuosity, or sharp angulations-will be considered eligible. Once the variant is confirmed, and oral consent provided, patients will be randomized in a 1:1 ratio to arterial navigation using either the standard hydrophilic 0.035'' guidewire-first technique or the Serpentine technique. At the end of the procedure informed consent will be signed. The study will involve operators-interventional cardiologists who will have been trained in the technique.

Baseline demographic, clinical, and laboratory parameters will be recorded, including age, sex, medical history, and indications for angiography. Additionally, the anatomical location of the loop or tortuosity will be recorded.

Inclusion Criteria:

• Age ≥18 years
• Feasibility of TRA
• Indication for coronary angiography
• Angiographic documentation of radial or brachial artery loop/tortuosity
• Written informed consent

Exclusion Criteria:

• STEMI - high risk NSTEMI presentation
• Hemodynamic instability
• Anatomical contraindications (e.g., arteriovenous fistula)
• Significant calcification of the radial or brachial artery on angiographic evaluation.