Study patients
From September 2011 to January 2012, asymptomatic heart transplanted recipients from the Heart Transplant Center of San Camillo - Forlanini Hospital in Rome were consecutively enrolled.
Study population comprised 25 patients who underwent DSE within 24 hours after MSCT coronary angiogram and, if the results of almost one of the two non-invasive diagnostic technique was positive, the patient underwent coronary angiography within 1 week after the tests, and if negative within 2 months. All patients were in sinus rhythm and on optimal and maximal tolerated pharmacological therapy, according to current guidelines for treatment and management of cardiac transplant [14]. Ongoing medical therapy was kept unchanged at the time of the stress test. No patients had implantable cardioverter-defibrillators or pacemakers. The exclusion criteria were: less than 12 months since transplant, iodinated contrast media allergy, signs or symptoms of CAV and New York Heart Association (NYHA) functional class IV. The sonographers were unaware of the results of the MSCT and of the coronary angiography.
The study complies with the Declaration of Helsinki. All patients gave written informed consent when they underwent stress echocardiography. When patients signed the consent forms, they also authorized physicians to use their clinical data according to Italian law.
Quality of life assessment
Quality of life has been assessed with the standard form of the SF–36 Health Survey (Version 1) [15], which has been used in a number of previous studies of organ-transplant candidates and recipients [16], with findings suggesting excellent validity and reliability. This test includes multiple-item scales to measure the following 8 health-related aspects: physical function (PF); role-physical (RP); bodily pain (BP); general health perceptions (GH); vitality (VT); social function (SF); role-emotional (RE); and mental health (MH). Scores were transformed into scores from 0 to 100, based on SF–36 scoring algorithms, where higher scores reflect better health [17]. SF-36 questionnaire was administered to the patients in the settings of DSE.
Stress protocol
Two-dimensional echocardiography and 12-lead electrocardiographic monitoring were performed in combination with high dose (up to 40 mcg/kg/min) dobutamine. Atropine infusion was considered if 85% of maximal heart rate wasn’t achieved at the end of DSE. During the procedure, blood pressure and the electrocardiogram were recorded each minute. Only representative cycles with optimal endocardial visualization were measured and the average of three measurements was taken. Images were acquired at baseline and at each 10-beat frequency increase during stress. LV volumes and ejection fraction were measured at rest and at each step using biplane Simpson rule. All volume measures were normalized by dividing by body surface area. Regional wall motion was assessed according to the recommendations of the European Society of Echocardiography from 1 (normal) to 4 (dyskinetic) in a 16-segment model of the left ventricle [18]. The blood pressure recording was made using a sphygmomanometer and the diaphragm of a standard stethoscope [19].
Non-echocardiographic criteria for ending the test were peak dobutamine, achievement 85% of target heart rate, (determined according to the equation: 220 – age), intolerable chest pain, excessive increase in blood pressure (defined as systolic blood pressure > 220 mm Hg; diastolic blood pressure > 120 mm Hg), hypotension (relative or absolute: > 30 mm Hg decrease in blood pressure), sustained supraventricular arrhythmias (supraventricular tachycardia or atrial fibrillation), ventricular arrhythmias (ventricular tachicardia, frequent, polymorphous premature ventricular beats), bradyarrhythmias. A maximal test was defined by the achievement of 85% of age-predicted maximal heart rate.
End-systolic pressure–volume determination
ESPVR was defined as the ratio of the systolic blood pressure (SBP)/end-systolic volume index (ESVi). The slope of the relationship was calculated as the ratio between SBP/ESVi and heart rate increase (from baseline to peak stress). The ESPVR was defined up-sloping when dobutamine-induced SBP/ESVi increase was higher than 25th percentile values of the entire study group, flat when below the 25th percentile values; biphasic, with an initial up-sloping followed by a later down-sloping trend, when peak dobutamine SBP/ESVi was lower than intermediate stress values [20, 21]. The critical heart rate was defined as the heart rate at which SBP/ESVi reached the maximum value during progressive increase in heart rate. In biphasic pattern, the critical heart rate was the heart rate beyond which SBP/ESVi declined by 5%.
Clinical follow-up
The patients were observed prospectively for 6 months with regular monthly outpatient visits. Adverse cardiovascular events were registered. The events considered were death, non-fatal acute myocardial infarction, and heart failure.
Statistics
Statistical analyses were performed using SPSS, version 17.0 (SPSS, Inc., Chicago, IL) for Windows. We assumed the coronary angiography as the reference standard for the identification of CAV. Results of MSCT and DSE (with and without ESPVR) were compared to the coronary angiography’s ones in order to evaluate diagnostic accuracy of the non-invasive tests. Distribution of relevant variables was summarized using frequencies, means, medians and standard errors (SEs), as appropriate. Univariate analysis was performed to compare the differences between ESPVR with continuous variables, using Fisher’s exact test and the Student unpaired t-test. Differences between groups and quality of life measures were analyzed using tests for non-normally distributed samples, as appropriate. To address the potential problem of error rate with multiple testing, Bonferroni–Holm adjustments were performed. All probability values were obtained using 2-sided analyses; p ≤ 0.05 was considered statistically significant for all analyses.
