Patients with advanced chronic kidney disease (CKD) have a high burden of coronary artery disease (CAD), which is frequently diffuse, heavily calcified, involves the left main coronary artery (LM), and coexists with comorbidities that may limit the suitability of surgical revascularization. At the same time, these patients are less likely to undergo invasive coronary assessment. More than two decades ago, this phenomenon was termed “renalism”, referring to the declining use of coronary angiography with worsening renal function despite an appropriate clinical indication [1]. This reluctance is largely related to concerns about contrast-associated acute kidney injury (CA-AKI), which is linked to prolonged hospitalization, initiation of renal replacement therapy, and increased mortality [2]. In patients with stage G5 CKD, the risk of precipitating dialysis may therefore substantially influence decisions regarding invasive diagnosis and treatment. Consequently, patients with a high ischemic burden may be less likely to receive guideline-directed invasive management [1].

In this context, the case reported in the present issue of Advances in Interventional Cardiology, describing intravascular ultrasound (IVUS) guided ultra-low contrast (ULC) percutaneous coronary intervention (PCI) of a heavily calcified distal LM lesion in a patient with stage G5 CKD, is particularly relevant [3]. It illustrates that advanced renal dysfunction does not necessarily preclude complex PCI when contrast exposure is systematically minimized.

The rationale underlying this approach is straightforward. Contrast angiography provides information on vessel dimensions, lesion length, calcium distribution, device position, stent expansion and apposition, and procedural complications. Many of these parameters can be assessed more accurately with intravascular imaging. Systematically replacing angiographic assessment with intravascular imaging and fluoroscopic landmarks therefore allows contrast administration to be restricted to selected procedural steps. Current terminology distinguishes zero-contrast PCI, in which no contrast is administered, from ULC PCI, commonly defined by a total contrast volume not exceeding the eGFR, corresponding to a contrast volume-to-eGFR ratio of ≤ 1 [4]. This approach reflects the concept of adjusting contrast exposure to the degree of renal dysfunction rather than solely to body weight.

A reproducible ULC strategy requires prospective procedural planning and consistent application throughout the intervention. Its principal components have been described in structured protocols and are illustrated by the present case [3, 5, 6] and summarized in Table I. Of note, catheter engagement may be confirmed without contrast by intracoronary saline injection, which produces transient ECG changes when the catheter is appropriately positioned in the coronary ostium and may also be useful during diagnostic angiography [5]. More generally, contrast administration should be restricted to predefined safety checkpoints, primarily to exclude major complications such as perforation, flow-limiting dissection, or no-reflow.

Evidence supporting contrast-sparing PCI has increased substantially. The randomized MOZART trial demonstrated an approximately threefold reduction in contrast volume with IVUS-guided compared with angiography-guided PCI, without compromising procedural success [7]. Subsequent registry data have supported the feasibility and safety of ultra-low and zero-contrast PCI in broader clinical populations [8, 9], while prospective studies have evaluated this strategy specifically in patients with severe CKD [10]. A systematic review and meta-analysis has also compared zero- and ultra-low-contrast approaches with conventional PCI in patients with advanced CKD [11]. Importantly, reducing contrast exposure does not necessarily require a compromise in procedural quality. Intravascular imaging guidance has improved clinical outcomes in patients undergoing complex PCI in adequately powered randomized trials [12]. ULC PCI may therefore be considered an extension of contemporary imaging-guided PCI in which contrast exposure is systematically minimized.

The case is particularly instructive because of the complexity of the coronary anatomy. Severe, nearly circumferential calcification of a distal LM lesion represents a setting in which angiography has important limitations and intravascular imaging provides substantial additional information. IVUS allows characterization of calcium severity and distribution, facilitates selection of an appropriate lesion-modification strategy, and enables assessment of the effects of intravascular lithotripsy and subsequent stent expansion. These considerations are especially important in the LM, where inadequate stent expansion is particularly associated with adverse clinical outcomes. Thus, patients in whom contrast reduction is most important frequently have anatomical characteristics that independently provide a strong indication for intravascular imaging. The choice of femoral access in this patient, intended to preserve both radial arteries for potential future arteriovenous fistula creation, similarly illustrates the importance of incorporating the anticipated course of renal disease into procedural planning.

Two additional considerations deserve attention. First, procedural measures remain central to the prevention of CA-AKI because pharmacological prophylaxis has not demonstrated consistent benefit. In a large randomized trial involving patients with CKD undergoing angiography, neither intravenous sodium bicarbonate nor oral acetylcysteine reduced clinically relevant renal outcomes [13]. Preventive management therefore relies primarily on avoidance of nephrotoxic agents, minimization of contrast exposure relative to renal function, and appropriate periprocedural hydration. Hydration requires particular attention in patients with concomitant heart failure, in whom excessive volume administration may be poorly tolerated. In such patients, the left ventricular end-diastolic pressure (LVEDP)-guided hydration strategy evaluated in the POSEIDON trial provides one approach to individualizing fluid administration according to filling pressures [14].

Second, contrast-sparing strategies are increasingly being applied to structural heart interventions. Zero- and ultra-low-contrast transcatheter aortic valve implantation using non-contrast computed tomography and echocardiographic or intravascular imaging guidance has been reported in patients with impaired renal function, with outcomes comparable to conventional approaches [15]. In patients requiring staged coronary and structural interventions, cumulative contrast exposure across the entire treatment pathway should therefore be considered during procedural planning rather than assessing each procedure independently.

Several practical and evidentiary issues remain. Contrast volume and the contrast volume-to-eGFR ratio should be reported systematically in studies of complex PCI, alongside established procedural parameters such as fluoroscopy time and dose area product, to facilitate comparisons across studies. Because optical coherence tomography generally requires contrast administration for blood clearance, IVUS is better suited to patients in whom substantial contrast restriction is required. Contrast-reduction systems, automated injection systems, and careful manifold management may further reduce contrast exposure but should be regarded as adjuncts to, rather than substitutes for, an imaging-based procedural strategy. Finally, adequately powered randomized studies evaluating clinically meaningful renal endpoints – including the need for dialysis and mortality – would further define the clinical benefit of ULC and zero-contrast PCI in patients with advanced CKD. Such studies should also assess whether systematic implementation of contrast-sparing strategies may help reduce “renalism” by increasing access to clinically indicated invasive coronary assessment and revascularization in patients with advanced CKD.

The techniques required for ULC PCI are available in contemporary catheterization laboratories with expertise in intravascular imaging and complex PCI. Their effective implementation, however, requires a standardized workflow and familiarity with contrast-sparing techniques before they are applied to patients with advanced renal dysfunction and complex coronary anatomy. The case presented in this issue [3] demonstrates the feasibility of this strategy in stage G5 CKD and complex calcified LM disease. More broadly, it illustrates how systematic integration of intravascular imaging, procedural planning, and selective contrast administration may allow clinically indicated PCI to be performed while minimizing renal risk in patients with advanced CKD.