case_images: PMC11694668_01
case_images: Resting electrocardiogram in the supine position. Inappropriate sinus tachycardia (heart rate 105 b.p.m.) and left bundle brunch block.
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case_images: Pre-exam electrocardiogram in the supine position (Figure 1) showed inappropriate sinus tachycardia (resting HR 105 b.p.m.). Functional limitation prevented visualization of the second ventilatory threshold (Figure 2C and Table 1). Again, it was not possible to visualize the second ventilatory threshold (Figure 3 and Table 1).
case_images: Cardiopulmonary exercise testing graphs obtained during the first test (off-therapy) with a ramp protocol of 20 W/min. Heart rate (HR) and oxygen pulse (VO2/HR) over time (A); heart rate (HR) and carbon dioxide production (VCO2) over oxygen consumption (VO2) (B); ventilation/oxygen consumption (VE/VO2) and ventilation/carbon dioxide production (VE/VCO2) over time (C). The black arrow indicates the first ventilator threshold.
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case_images: This was followed by a near-plateau in both HR and oxygen pulse (a surrogate for stroke volume), indicating a limited capacity to further increase cardiac output during exertion (Figure 2A). Functional limitation prevented visualization of the second ventilatory threshold (Figure 2C and Table 1).
case_images: Cardiopulmonary exercise testing graphs obtained during the second test (ivabradin 5 mg b.i.d.) with a ramp protocol of 20 W/min. Heart rate (HR) and oxygen pulse (VO2/HR) over time (A); heart rate (HR) and carbon dioxide production (VCO2) over oxygen consumption (VO2) (B); ventilation/oxygen consumption (VE/VO2) and ventilation/carbon dioxide production (VE/VCO2) over time (C). The black arrow indicates the first ventilator threshold.
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case_images: Again, it was not possible to visualize the second ventilatory threshold (Figure 3 and Table 1).
case_images: Cardiopulmonary exercise testing graphs obtained during the third test (ivabradin 5 mg b.i.d. plus metoprolol 50 mg b.i.d.) with a ramp protocol of 20 W/min. Heart rate (HR) and oxygen pulse (VO2/HR) over time (A); heart rate (HR) and carbon dioxide production (VCO2) over oxygen consumption (VO2) (B); ventilation/oxygen consumption (VE/VO2) and ventilation/carbon dioxide production (VE/VCO2) over time (C). The black arrow indicates the first ventilator threshold, the grey arrow the second ventilator threshold.
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case_images: At the third follow-up (ivabradine + beta-blocker), 1 month after the previous one, there was a marked improvement in the maximum workload achieved (220 W vs. 160 W at the first check), oxygen consumption (29.2 mL/min/kg, 101% of the predicted value), a continuously increasing oxygen pulse curve with a further reduction in peak HR (max HR 161 b.p.m.) (Figure 4A and B). Additionally, the improved overall exercise capacity translated into greater exploitation of anaerobic lactate metabolism (indicated by visualization of the second ventilatory threshold) (Figure 4C).