Anti-ischemic therapy and stress testing: pathophysiologic, diagnostic and prognostic implications

Assessment of the routine reporting of very low-dose exercise-first myocardial perfusion SPECT from a large-scale real-world cohort and correlation with the subsequent reporting of coronary stenosis at angiography

PURPOSE

Our study assesses the routine reporting of exercise ischemia using very low-dose exercise-first myocardial perfusion SPECT in a large number of patients and under real-life conditions, by evaluating correlations with the subsequent routine reporting of coronary stenosis by angiography and with factors that predict ischemia.

METHODS

Data from 13,126 routine exercise MPI reports, from 11,952 patients (31% women), using very low doses of sestamibi and a high-sensitivity cardiac CZT camera, were extracted to assess the reporting of significant MPI-ischemia (> 1 left ventricular segment), to determine the MPI normalcy rate in a group with < 5% pretest probability of coronary artery disease (CAD) (n = 378), and to assess the ability of MPI to predict a > 50% coronary stenosis in patients with available coronary angiography reports in the 3 months after the MPI (n = 713).

RESULTS

The median effective patient dose was 2.51 [IQR: 1.00-4.71] mSv. The normalcy rate was 98%, and the MPI-ischemia rate was independently predicted by a known CAD, the male gender, obesity, and a < 50% LV ejection fraction, ranging from 29.5% with all these risk factors represented to 1.5% when there were no risk factors. A > 50% coronary stenosis was significantly predicted by MPI-ischemia, less significantly for mild (odds ratio [95% confidence interval]: 1.61 [1.26-1.96]) than for moderate-to-severe MPI-ischemia (4.05 [3.53-4.57]) and was also impacted by having a known CAD (2.17 [1.83-2.51]), by a submaximal exercise test (1.48 [1.15-1.81]) and being ≥ 65 years of age (1.43 [1.11-1.76]).

CONCLUSION

Ischemia detected using a very low-dose exercise-first MPI protocol in a large-scale clinical cohort and under real-life routine conditions is a highly significant predictor for the subsequent reporting of coronary stenosis, although this prediction is enhanced by other variables. This weakly irradiating approach is amenable to being repeated at shorter time intervals, in target patient groups with a high probability of MPI-ischemia.

By discontinuing beta-blockers before an exercise test we may precipitate a rebound phenomenon

BACKGROUND

There is a need to analyse the current approach to beta-blocker (BB) use in relation to exercise-based stress tests.

OBJECTIVE

We compared various guidelines regarding recommending abrupt vs gradual discontinuation of BB prior to exercise tests. We also analyse the shortcomings of the currently recommended approach and suggest a new approach to avoid BB rebound.

METHODS

A narrative review is used to analyse this topic due to lack of valid randomized clinical trials.

RESULTS

Omitting the BB therapy prior to exercise-based test has been recommended in guidelines for many years. Although reasonable, this approach has potential disadvantages since sudden BB withdrawal may induce a rebound phenomenon, which is, also, acknowledged in several guidelines.

CONCLUSIONS

We observed inconsistency among relevant guidelines; there is no homogenous approach regarding BB use before exercise tests. Most guidelines recommend BB withdrawal for a couple of days before the test; they do not advise BB dose tapering. This approach is not standardised and raises the risk of BB rebound phenomenon both before and during the test. Therefore, we suggest using the half the prescribed BB dose at the usual time of administration (in the morning, prior to the exercise test).

Preprocedural β-Blockers in the Functional Assessment of Intermediate Coronary Lesions by Instantaneous Wave-Free Ratio

AIM

Instantaneous wave-free ratio (iFR) has emerged as the strategy of choice for the assessment of intermediate coronary lesions. The impact of preprocedural β-blockers therapy on the iFR was the aim of this study.

METHODS

We included patients undergoing functional assessment of intermediate (40%-70%) coronary lesions in 2 centers. The iFR measurement was performed by pressure-recording guidewire and calculated at the core laboratory using the manufacturers' dedicated software. Minimal luminal diameter, reference diameter, percent diameter stenosis, and length of the lesion were measured. Positive iFR was considered for values <0.90.

RESULTS

We included 197 patients undergoing functional evaluation of 223 coronary lesions. Patients on β-blockers (69%) had more frequently hypertension (P = .05); previous myocardial infarction (P = .01); therapy with clopidogrel (P = .02), statins, and aspirin; and acute coronary syndrome at presentation (P < .001, respectively). Mean iFR values were slightly higher in patients on β-blockers (0.94 ± 0.06 vs 0.92 ± 0.06, P = .11). The rate of positive iFR was significantly lower with β-blockers (14.9% vs 27.5%, P = .04). On multivariate analysis, β-blockers use was a predictor of the significance of coronary stenoses (odds ratio [OR] = 0.48; 95% CI = 0.23-0.98; P = .05) together with lesion length (OR = 1.04; 95% CI = 1.01-1.07; P = .007).

CONCLUSION

Among patients undergoing iFR, preprocedural β-blockers are associated with higher absolute values and a lower rate of positive iFR.

Comparison of heart rate reserve, age predicted maximum heart rate and rate pressure product as predictors of future cardiovascular events following a negative dobutamine stress echocardiogram

Background: Dobutamine stress echocardiography (DSE) is a commonly used diagnostic stress test for the assessment of various cardiac pathologies on patients unable to perform exercise. Unlike exercise, there is no reliable subjective termination end-point such as fatigue to rely on. Consequently, DSE's are often concluded at a predetermined age predicted maximal heart rate (APMHR) such as 85%. The aim of this study was to assess if APMHR, heart rate reserve (HRR) and the maximum rate pressure product (MRPP) are valid measures of future cardiovascular (CV) events in otherwise negative DSEs. Methods: Following exclusions, receiver operating curve (ROC) analyses were performed on 652 patients using CV events during the follow-up period (4.2 ± 1.8 years) as the outcome variable. Results: ROC analyses failed to produce a statistically valid model for MRPP (p = .227, area under curve (AUC)=0.55) with a sensitivity and specificity of 21.1% and 91.9%, respectively at the optimal cut point (14948 MRPP). To the contrary, APMHR produced a sensitivity and specificity of 74.7% and 60.9%, respectively (p < .0001, AUC = 0.715). HRR however, with a sensitivity and specificity of 67.4% and 68.2% (p < .0001, AUC = 0.718) was the only predictor of CV events following Cox analysis (p < .0001). Conclusions: This study demonstrates MRPP as a poor measure of CV event prediction during DSE. While an APMHR of 89.3% demonstrated a statistically valid model, HRR was the only predictor of CV events in otherwise negative DSEs.

Stress echocardiography in coronary artery disease: a practical guideline from the British Society of Echocardiography

Stress echocardiography is an established technique for assessing coronary artery disease. It has primarily been used for the diagnosis and assessment of patients presenting with chest pain in whom there is an intermediate probability of coronary artery disease. In addition, it is used for risk stratification and to guide revascularisation in patients with known ischaemic heart disease. Although cardiac computed tomography has recently been recommended in the United Kingdom as the first-line investigation in patients presenting for the first time with atypical or typical angina, stress echocardiography continues to have an important role in the assessment of patients with lesions of uncertain functional significance and patients with known ischaemic heart disease who represent with chest pain. In this guideline from the British Society of Echocardiography, the indications and recommended protocols are outlined for the assessment of ischaemic heart disease by stress echocardiography.

Effects of β-Blockers on Maximal Heart Rate Prediction Equations in a Cardiac Population

PURPOSE

To derive specific maximal heart rate (HRmax) prediction equations for a coronary artery disease (CAD) population based upon status of β-blocker (BB) therapy and to compare these to prior HRmax equations (Fox and Brawner-specific for CAD).

METHODS

We retrospectively reviewed stress echocardiogram treadmill tests in patients with CAD, dividing subjects into 3 groups based upon BB use on test day: not prescribed BB therapy (no BB group; n = 110); held for 12 to 24 hr prior (held BB group; n = 155); and continued taking (took BB group; n = 72).

RESULTS

Derived HRmax equations for our CAD population were no BB = 200 - 0.79 × age; held BB = 193 - 0.71 × age; and took BB = 168 - 0.51 × age. Achieved HRmax mean was not significantly different between held BB and no BB groups; however, HRmax in the took BB group was significantly lower. Fox and Brawner (no BB)-HRmax equations significantly overestimated (+6 and +9 mean bias) and underestimated (-8 and -6 mean bias) achieved HRmax in no BB and held BB groups, respectively. The Brawner (no BB) equation intercept and slope were not significantly different from our CAD-held BB and no BB equations. The Brawner (on BB) equation intercept and slope were similar to our took BB equation, but greatly underestimated achieved HRmax (-17 mean bias).

CONCLUSION

For patients holding BB therapy on test day, a similar CAD HRmax estimation equation to those patients never on BB can be used, comparable to the Brawner (no BB) equation. Further research is needed to determine when patients should take their BB therapy in conjunction with exercise testing.

Southern Hospitality: How We Changed the NPO Practice in the Emergency Department

PROBLEM

In the Vanderbilt Medical Center adult emergency department, the practice has been to keep patients on "nothing by mouth" (NPO) status throughout their assessment, diagnostic, and treatment phases. As a result, most patients have NPO status for a period of several hours to days. The consequences are patient discomfort, hunger, thirst, dehydration, interruptions in routine medication schedules, poor glucose control, and compromised acid/base balance. The purpose of this project was to modify the NPO practice in the adult emergency department.

METHODS

A survey of nursing staff perceptions demonstrated both staff and patient dissatisfaction with the NPO practice. Responses to postdischarge satisfaction surveys demonstrated that patients experienced some discomfort because of hunger or thirst. A search of the literature revealed that the American Society of Anesthesiologists (ASA) adopted guidelines in 1999 that patients should fast 6 hours from solids and 2 hours from liquids preoperatively. These guidelines were implemented in the adult emergency department using the Standard Rollout Process. Physician order sets for the emergency department and the ED chest pain unit were modified to reflect the ASA guidelines.

RESULTS

After implementation of the ASA guidelines, a follow-up survey of nursing staff showed increased staff and patient satisfaction. After implementation, the patient satisfaction survey demonstrated an increase in patients who reported "no discomfort" because of hunger or thirst. No adverse outcomes or delays were reported in relation to the change in NPO standards. This change in practice resulted in improved satisfaction for patents and staff.

IMPLICATIONS FOR PRACTICE

The ASA guidelines have been in existence for more than a decade. They are evidence based. The role of the nurse is to advocate for the patient. Nurses need to be proactive in determining the timing of procedures and asking physicians to give diet orders that are in accordance with the ASA guidelines.

Target heart rate to determine the normal value of coronary flow reserve during dobutamine stress echocardiography

BACKGROUND

The determination of coronary flow reserve (CFR) is an essential concept at the moment of decision-making in ischemic heart disease. There are several direct and indirect tests to evaluate this parameter. In this sense, dobutamine stress echocardiography is one of the pharmacological method most commonly used worldwide. It has been previously demonstrated that CFR can be determined by this technique. Despite our wide experience with dobutamine stress echocardiography, we ignored the necessary heart rate to consider sufficient the test for the analysis of CFR. For this reason, our main goal was to determine the velocity of coronary flow in each stage of dobutamine stress echocardiography and the heart rate value necessary to double the baseline values of coronary flow velocity in the territory of the left anterior descending (LAD) coronary artery.

METHODS

A total of 33 consecutive patients were analyzed. The patients included had low risk for coronary artery disease. All the participants underwent dobutamine stress echocardiography and coronary artery flow velocity was evaluated in the distal segment of LAD coronary artery using transthoracic color-Doppler echocardiography.

RESULTS

The feasibility of determining CFR in the territory of the LAD during dobutamine stress echocardiography was high: 31/33 patients (94%). Mean CFR was 2.67 at de end of dobutamine test.There was an excellent concordance between delta HR (difference between baseline HR and maximum HR) and the increase in the CFR (correlation coefficient 0.84). In this sense, we found that when HR increased by 50 beats, CFR was ≥ 2 (CI 93-99.2%). In addition, 96.4% of patients reached a CFR ≥ 2 (IC 91.1 - 99%) at 75% of their predicted maximum heart rate.

CONCLUSIONS

We found that the feasibility of dobutamine stress echocardiography to determine CFR in the territory of the LAD coronary artery was high. In this study, it was necessary to achieve a difference of 50 bpm from baseline HR or at least 75% of the maximum predicted heart rate to consider sufficient the test for the analysis of CFR.

Impact of previous myocardial infarction on the incremental value of myocardial contrast to two-dimensional supine bicycle stress echocardiography in evaluation of coronary artery disease

BACKGROUND

If compared to two-dimensional echocardiography (2DE), myocardial contrast echocardiography (MCE) improves detection of coronary artery disease (CAD) during pharmacological stress, but data on MCE vs. 2DE during supine bicycle stress is limited. Although previous myocardial infarction (MI) influences sensitivity of 2DE, its effect on MCE has not been evaluated.

OBJECTIVES

The study sought to determine the incremental benefit of MCE over 2DE for evaluation of CAD during supine bicycle stress and to assess the impact of previous MI on diagnostic values of both methods.

METHODS

We studied 103 consecutive patients scheduled for coronary angiography. Prior to coronary angiography, all patients underwent supine bicycle stress. 2DE and MCE were performed during this stress test. The diagnosis of obstructive CAD (> or =50% stenosis) was based on the presence of inducible wall motion and perfusion abnormalities.

RESULTS

Quantitative coronary angiography revealed > or =50% stenosis in 53 of 77 patients without previous MI and in 21 of 26 patients with previous MI. If compared to 2DE, MCE was more sensitive (68% vs. 86%; p<0.001) and more accurate (73% vs. 86%; p < 0.001) to detect > or =50% stenosis. In patients without previous MI, 2DE and MCE yielded sensitivity of 65% and 85% (p < 0.01) and accuracy of 71% and 85% (p < 0.01), whereas in patients with previous MI sensitivity was 79% and 90% (p=NS) and accuracy 79% and 88% (p = NS), respectively.

CONCLUSIONS

MCE enhances sensitivity and accuracy of 2DE in detection of obstructive CAD during supine bicycle stress. The incremental benefit of MCE is especially present in patients without previous MI.

Prognostic implications of dipyridamole or dobutamine stress echocardiography for evaluation of patients > or =65 years of age with known or suspected coronary heart disease

This study investigated the value of pharmacologic stress echocardiography for risk stratification of patients > or =65 years of age. The study cohort consisted of 2,160 patients > or =65 years of age (1,257 men, mean +/- SD 71 +/- 5 years of age) undergoing dipyridamole (n = 1,521) or dobutamine (n = 639) stress echocardiography for evaluation of known (n = 913) or suspected (n = 1,247) coronary artery disease. Of 2,160 patients, 753 (35%) had a normal test result, whereas 772 (36%) showed a myocardial ischemic pattern and 635 (29%) a scar pattern. During a median follow-up of 26 months, 241 deaths and 87 nonfatal myocardial infarctions occurred. Patients (n = 568) undergoing revascularization were censored. Of 16 analyzed variables, age (hazard ratio [HR] 1.07 per unit increment), wall motion score index at rest (HR 2.63 per unit increment), ischemia at stress echocardiography (HR 1.81), and diabetes (HR 1.57) were multivariable predictors of death, whereas age (HR 1.06 per unit increment), ischemia at stress echocardiography (HR 2.60), wall motion score index at rest (HR 1.98 per unit increment), scar pattern (HR 1.99), and diabetes (HR 1.48) were multivariable predictors of death or myocardial infarction. Using an interactive stepwise procedure, stress echocardiography showed incremental prognostic value over clinical and echocardiographic data at rest, which decreased with increasing age. In addition, the annual hard event rate associated with a normal test result progressively increased with age. In conclusion, pharmacologic stress echocardiography provides useful prognostic information in patients > or =65 years of age. However, its prognostic value decreases with increasing age.

[Preoperative cardiac assessment using dobutamine stress echocardiography]

Postoperative myocardial ischaemia is the leading cause of life expectancy impairment after high cardiac risk surgical procedures. Preoperative identification of patients at high risk for such complication helps reducing its postoperative incidence through therapeutic adjustments. The former relies upon preoperative selection of patients who are candidates for cardiac testing using dobutamine stress echocardiography, according to ACC/AHA guidelines. This exam evaluates echographic myocardial response to a pharmacological stress induced by dobutamine infusion. Its aim is to reproduce part of the stress the myocardium will undergo during surgical procedure. A stress induced myocardial ischaemia suggests such a complication could occur postoperatively. A positive dobutamine stress echocardiography justifies to prescribe preoperative anti-ischaemic treatment in order to reduce the cardiac risk of the further surgical procedure. Moreover, it justifies clear definition of perioperative haemodynamic objectives. Whatever the result of the dobutamine stress echocardiography, cardiac ischaemia should be monitored up to the third postoperative day on the basis of a daily 12-lead electrocardiogram recording and daily plasmatic troponin Ic measurement.

Incremental diagnostic value of ultrasonographic assessment of coronary flow reserve with high-dose dipyridamole in patients with acute coronary syndrome

BACKGROUND

Coronary flow reserve (CFR) assessment by transthoracic Doppler echocardiography has been found to be useful in subjects with suspected coronary artery disease. An important clinical question is whether such technique can be successfully applied in patients admitted to the coronary care unit with an acute coronary syndrome to detect a significant left anterior descending (LAD) disease.

METHODS

One hundred fifty-nine patients with acute coronary syndrome (93 patients with unstable angina, 66 with acute inferior or lateral myocardial infarction) were included in the present analysis. Patients underwent a high-dose dipyridamole stress (0.84 mg/kg) with combined assessment of CFR in the LAD and regional wall motion. Blood flow velocities were recorded in the mid-distal portion of the LAD using a digital ultrasonographic system and CFR was calculated as the ratio of hyperemia-induced peak diastolic velocity to resting peak diastolic flow velocity. All patients underwent coronary angiography and a significant LAD stenosis was classified for lumen narrowing > or = 70%.

RESULTS

Adequate Doppler recordings in the LAD were obtained in 92% of patients. A contrast agent was used in the 39% of examinations. No major adverse reaction occurred in any patient. A receiving operating characteristic curve showed that a CFR value < 1.9 had a sensitivity of 85%, a specificity of 87%, a positive predictive value of 71%, a negative predictive value of 94% and a diagnostic accuracy of 86% for identifying a significant LAD stenosis. The area under the receiving operating characteristic curve computed for CFR was significantly higher than for wall motion score index (p < 0.001). In a stepwise forward, multiple logistic regression analysis, both CFR (OR = 4.8, 95% C.I. 3.7-5.3; p < 0.00001) and the wall motion score index for the LAD territory (OR = 4.2, 95% C.I. 2.6-6.8; p < 0.0001) were independent determinants of LAD stenosis > or = 70%.

CONCLUSION

Early assessment of CFR by transthoracic Doppler echocardiography is feasible and safe and provides additional information to identify subjects with acute coronary syndrome and significant LAD stenosis.

Pacing stress echocardiography

Background

High-rate pacing is a valid stress test to be used in conjunction with echocardiography; it is independent of physical exercise and does not require drug administration. There are two main applications of pacing stress in the echo lab: the noninvasive detection of coronary artery disease through induction of a regional transient dysfunction; and the assessment of contractile reserve through peak systolic pressure/ end-systolic volume relationship at increasing heart rates to assess global left ventricular contractility.

Methods

The pathophysiologic rationale of pacing stress for noninvasive detection of coronary artery disease is obvious, with the stress determined by a controlled increase in heart rate, which is a major determinant of myocardial oxygen demand, and thereby tachycardia may exceed a fixed coronary flow reserve in the presence of hemodynamically significant coronary artery disease. The use of pacing stress echo to assess left ventricular contractile reserve is less established, but promising. Positive inotropic interventions are mirrored by smaller end-systolic volumes and higher end-systolic pressures. An increased heart rate progressively increases the force of ventricular contraction (Bowditch treppe or staircase phenomenon). To build the force-frequency relationship, the force is determined at different heart rate steps as the ratio of the systolic pressure (cuff sphygmomanometer)/end-systolic volume index (biplane Simpson rule). The heart rate is determined from ECG.

Conclusion

Two-dimensional echocardiography during pacing is a useful tool in the detection of coronary artery disease. Because of its safety and ease of repeatability noninvasive pacing stress echo can be the first-line stress test in patients with permanent pacemaker.

The force-frequency can be defined as up- sloping (normal) when the peak stress pacing systolic pressure/end-systolic volume index is higher than baseline and intermediate stress values, biphasic with an initial up- sloping followed by a later down-sloping trend, or flat or negative when peak stress pacing systolic pressure/end-systolic volume index is equal or lower than baseline stress values. This approach is certainly highly feasible and allows a conceptually immaculate definition of contractility with prognostic usefulness, but its therapeutic implications remains to be established. Bowditch treppe, assessed with pacing stress, can be used to assess the optimal stimulation frequency and to optimise the patient's chronotropic response in programming rate-adaptive pacemakers.