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Sumario Vol. 42 - Nº 3 Julio - Septiembre 2013

Clinical Value of Normal Myocardial Perfusion SPECT
with Positive Stress Exercise

Miguel Hominal, Gerardo Zapata, Paola Llanes, Jorge Lopez

Servicio de Cardiología Nuclear. Instituto Cardiovascular de Rosario
Bv. Oroño 450. (2000) Rosario, Santa Fe, Argentina.
E mail

Recibido 07-FEB-2013 – ACEPTADO después de revisión el 04-JULIO-2013.

The authors declare not having a conflict of interest.
Rev Fed Arg Cardiol. 2013; 42(3): 195-199


Print version Imprimir sólo la columna central

 

 

RESUMEN

El SPECT cardíaco resulta útil para establecer diagnóstico y pronóstico en la cardiopatía isquémica. Se ha descrito baja prevalencia de estudios de perfusión miocárdica (PM) normales con electrocardiograma de esfuerzo positivo (+), y baja tasa de mortalidad e incidencia de infarto (IAM).
Objetivos: Determinar pronóstico a mediano plazo de pacientes con prueba ergométrica (PEG) + por infradesnivel del ST (IST) y PM normal.
Materiales y Métodos: Se analizaron los SPECT cardíacos realizados con PEG durante 2 años. Se incluyeron aquellos con PEG + y se excluyeron los que presentaron PM anormal. Se realizó seguimiento clínico evaluando eventos cardiovasculares (ECV) mayores y menores.
Resultados: De 6.373 estudios 507 (7,9%) fueron PEG +, el 2,3% (n=151) no presentaron defectos de PM. La edad media fue 59 años y 68% de sexo masculino. El 31,8% presentaban antecedentes de revascularización, 8,6% de angina inestable y 4,6% de IAM. Las causas de realización del SPECT fueron: PEG anormal previa, valoración del status post angioplastia coronaria y detección de cardiopatía isquémica en asintomáticos. El 92,1% resultaron suficientes, siendo detenidas en su mayoría por agotamiento. El IST medio fue de 1,9 ± 0,6 mm y su aparición fue más frecuente en la recuperación. Sólo 11,9% presentaron angina. Se realizó seguimiento clínico en 92% (15,4 ± 5,6 meses). No se registró la presencia de muerte ni IAM no fatal, siendo los ECV en su totalidad menores (4,3%).
Conclusiones: En nuestro estudio los pacientes con una PM sin isquemia tienen buen pronóstico, aún con una PEG eléctricamente +.

Palabras clave: Estudios de perfusión miocárdica. Pronóstico. SPECT.
SUMMARY

Myocardial perfusion (MP) test, such us cardiac SPECT, are commonly used to determinate diagnosis and prognosys in coronary artery disease. It is already known the low prevalence of normal MP studies with a positive treadmill exercise test (TET), which has a very good prognosis.
Objetives: To determinate the prognosis of patients with a positive TET by ST depression (STD) and normal MP test.
Methods: Among 6373 patientes included in our batabase, we analized 507 with positive TET and normal perfusion images. Clinical follow-up was realized considering major (death and MI) and minor (revascularization-RV-, cardiac failure and unestable angina-UA-) cardiac events (CE).
Results: Just 7.9% of TET resulted positive by STD and 2.3% presented normal MP. The average age was 59 years and 68% were men. Hypertension and dyslipidemia were the most prevalent risk factors. Previous RV was present in 31.8%, UA in 8.6% and MI in 4.6%. The most common cause of SPECT evaluation was a previous abnormal TET (22.5%), followed by control after percutaneous RV and diagnosis in asymptomatic patients (21.9%). The average STD was 1.9 ± 0.6 mm. Only 11.9% presented angina during the exercise. 92% of the patients were followed up for twelve months. No major CE was reported and the prevalence of combined CE was 4.3%.
Conclusions: No patient presented dead or MI alter a normal MP test, even with a positive TET, which shows the good prognosis of this subgroup of patients.

Key words: Myocardial perfusion test. Prognosis. SPECT.

 

 

 

INTRODUCTION
Myocardial perfusion (MP) is one of the most widely used methods currently for the diagnosis and prognostic evaluation of patients with suspicion of ischemic heart disease or known CAD. Its high diagnostic sensibility has been reported in multiple trials and from the prognostic point of view, different publications have shown that the patients with chest pain that have a negative MP study have a good prognosis with a yearly risk of death and infarction below 1%[1-2]. This good prognosis was observed even in patients with ischemic ST segment changes [3-7]. However, on occasions, the normal perfusion images are associated to positive stress test (GXT) by ST segment depression, generating doubts on the veracity of the diagnostic information, since it could be a false negative of the SPECT or a false positive of the GXT. Some reports have informed about the existence of situations that have been called “balanced ischemia” when we are before a patient with 3-vessel disease and the subsequent induction of ischemia in a homogeneous fashion in multiple territories may resemble a normal study [8-9].

With the goal of analyzing with what frequency the association of normal cardiac SPECT studies with positive GXT, the characteristics of the population and the prognosis in the mid term of patients with these results are observed, we have reviewed cardiac SPECT studies performed in our service for 2 years.

 

MATERIAL AND METHODS

Population

All cardiac SPECT studies were analyzed consecutively. The SPECT studies were made by stress in treadmill since September 2009 until September 2011 in our center. From them (n=6,373), only those with positive stress test and normal perfusion images were selected (n=507).

Ergometer test
An ergometer test was considered positive when there was ST segment depression with horizontal morphology ≥1 mm, ST segment depression with descending slope and ST segment elevation ≥1 mm, all at 80 ms from the J point in absence of Q waves, regardless of the presence of symptoms.

Patients with baseline electrocardiogram (ECG), with repolarization disorders that made a proper analysis difficult were excluded, as well as those with positive stress test and whose studies showed abnormal myocardial perfusion by SPECT, both fixed perfusion defects (fibrosis) and reversible ones (ischemia) and those with attenuation by mammary gland tissue or diaphragmatic interposition in whom, some degree of ischemia or fibrosis could not be ruled out.

Cardiac SPECT
A digital General Electric VENTRI dual head SPECT Gamma camera was used, with high resolution collimator. After the administration of 8 mCi of Tc99m sestamibi, images were obtained of myocardial uptake of the radiotracer, following a “step and shoot” protocol of acquisition, with a circular orbit, starting in an anterior right oblique position at 45º. The study was stored in a matrix of 64 x 64. In the process of tomographic reconstruction, a Butterworth filter was used. Two hours later, the patient underwent ergometer test in treadmill, using a stress protocol limited by symptoms. During the maximal stress reached, 25 mCi of Tc99m sestamibi were administered. New images were obtained according to the protocol of acquisition explained above. For the processing of the images, softwares of the University of Emory (Cardiac Tool Box) and/or Guido Germano were used. The reconstructed images were interpreted as normal in the daily reading session in charge of a nuclear cardiologist.

The baseline characteristics of the population and the variables associated to the presence of ST segment depressionwere analyzed.

Follow-up
Clinical follow-up was made, evaluating cardiovascular events by phone contact and/or outpatient clinical visit. The cardiovascular events in follow-up were classified in major, minor, and combined. All-cause death and non-fatal acute myocardial infarction were considered major, and the need for revascularization (surgical or percutaneous) and admittance by unstable angina and heart failure were considered minor.

Statistical analysis
For the analysis of data, the IBM SPSS Statistics 19 program was used. The quantitative variables were expressed as average and standard deviation, while qualitative variables are expressed as numbers and percentages.

 

RESULTS
From a total 6373 GXT performed during the period analyzed, 7.9% (n=507) were positive for ST segment depression. From these, only those that did not present perfusion defects by SPECT (2.3%) were selected, constituting a sample of 151 patients.

With regard to the basal characteristics of the population (Table 1), the average age was approximately 59 years old (from 35 to 85 years), with most being males (68%). Hypertension was the most frequent risk factor (61.6%), followed by dyslipidemia (53.6%) and in a lower proportion, Diabetes Mellitus and smoking. As to the cardiovascular history, 31.8% of patients previously underwent revascularization procedures, both surgical and percutaneous, 8.6% mentioned prior admittance by unstable angina and 4.6% by acute myocardial infarction. Only 2% suffered stable chronic angina. Almost half of the patients were under antiischemic treatment (aspirin, beta blockers and statins).

 

%

n

Age average

59.5 ± 8.5

(35-85)

Sex male

68.2

103

Risk factors:

 

 

  Hypertension

61.6

93

  Dyslipidemia

53.6

81

  Diabetes Mellitus

17.9

27

  Smoking

10.6

16

  Inherited/familial history

18.5

28

  Sedentarism

36.4

55

Cardiovascular history:

 

 

  Stable chronic angina

2

3

  Unstable angina

8.6

13

  Acute myocardial infarction

4.6

7

  Revascularization

31.8

48

  Coronary angioplasty

29.8

45

  CABG

3.3

5

  Stroke

0.7

1

  Peripheral artery disease

1.3

2

Treatment:

 

 

  Aspirin

43.7

66

  Beta-blockers

45.7

69

  Anti-calcium agents

4.6

7

  Statins

39.1

59

Table I. Basal characteristics of the population

 

About the request of the study, the most frequent cause was the presence of prior abnormal ergometer test (positive or doubtful) in 22.5%, followed by assessment of the post-coronary angioplasty status (21.9%), detection of ischemic heart disease in asymptomatic patients (21.9%) and the presence of uncharacteristic chest pain (15.9%).

In regard to stress test, it was made with Bruce protocol in all patients, using facilitation with atropine in very few cases (2.6%). From all of them, 92.1% were sufficient, being submaximal in 60.9% and maximal in 31.1%. The most frequent cause to stop the test was exhaustion (64.9%), followed by maximal heart rate. Only 2.6% were stopped by angor. About the stress performed, 39.7% of patients reached stage III and 31.1% stage II.

ST segment depression was observed in an average of 1.9±0.6 mm, and the onset of appearance was more frequent in the stage of recovery (48.3%).

Only 11.9% of the patients presented symptoms compatible with angina during stress test. The rest of the variables associated to the stress test are reflected in Table II.

 

%

n

Reason for the study:

 

 

Abnormal ergometer test

22.5

34

Post-angioplasty status

21.9

33

Detection of ischemic heart disease

21.9

33

Uncharacteristic chest pain

15.9

24

Recent-onset angina

6.6

10

Detection of silent ischemia

2.6

4

Stress dyspnea

2

3

Ventricular arrhythmias

2

3

Post-CABG status

2

3

Medical treatment evaluation

1.3

2

Abnormal electrocardiogram

0.7

1

Unstable angina of low risk

0.7

1

Protocol used:

 

 

Bruce

97.4

147

Bruce associated to facilitation with atropine

2.6

4

Reason to stop:

 

 

Exhaustion

64.9

98

Maximal HR

32.5

49

Angor

2.6

4

Result:

 

 

Maximal

31.1

47

Submaximal

60.9

92

Insufficient

7.9

12

Load used:

 

 

Mets

8.73 ± 2.2

Maximal TTI

24.246 ± 4.515

Maximal stage reached:

 

 

I

9.9

15

II

31.1

47

III

39.7

60

IV

18.5

28

V

0.7

1

ST segment depression

 

 

Mean

1.9 ± 0.6 mm

Stage of onset

 

 

II

11.9

18

III

27.8

42

IV

11.9

18

Recovery

48.3

73

Blood pressure

 

 

Maximal systolic blood pressure

164.7 ± 22.6 mmHg

Paradoxical response

0.7

1

Table II. Stress Test

 

An assessment of ventricular function by gated SPECT was made in 36.4% of the patients, presenting in all cases post-stress EF, ventricular volumes and systolic thickening within normal parameters.

A clinical follow-up was made in 92% of the patients (n=139) with an average of 15.4±5.6 months. During this period, no major cardiac events were observed. Only 6 patients suffered minor events; 2 patients were admitted by non-ST elevation acute coronary syndromes, 3 patients were revascularized, 2 by surgery and 1 percutaneously, and 1 patient mentioned symptoms compatible with heart failure. The incidence of mixed cardiovascular events was 4.3%, all corresponding to minor cardiovascular events (Table III). From these 6 patients that presented events, 5 were studied angiographically with the results shown in Table IV.

 

%

n

Major cardiovascular events

0

0

Acute myocardial infarction

0

0

Death

0

0

Minor cardiovascular events

4.3

6

Unstable angina

1.4

2

Heart failure

0.7

1

Revascularization

2.1

3

Surgical

1.4

2

Percutaneous

0.7

1

Combined cardiovascular events

4.3

6

Table III. Clinical follow-up


Patients

Findings

Patient 1 (CABG)

Lesion 85% of LMCA

Patient2 (CABG)

Lesion of three vessels (ADA 75%, Dg 75%, occluded Cx, partial occlusion of RCA)

Patient 3 (PTCA)

Lesion of a vessel (Dg 80%).

Patient4 (ACS)

Lesion of a vessel (Ramus intermedius 75%).

Patient 5 (ACS)

Lesion of a vessel (Cx 80%) ADA and RCA with moderate lesions.

Patient 6 (CHF)

No angiographic study.

CABG: Coronary artery bypass grafting; LMCA: Left main coronary artery; ADA: Anterior descending artery; Dg: Diagonal artery; Cx: Circumflex artery; RCA: Right coronary artery; PTCA: Percutaneous transluminal coronary angioplasty; ACS: Acute coronary syndrome; CHF: Congestive heart failure.

Table IV. Angiographic results of patients with cardiovascular events

 

 

DISCUSIÓN
The prevalence of myocardial perfusion SPECT studies with positive ergometer tests by ST observed in our series was 2.3%, similar to what was described in other publications [10-11]. Unlike other reports, where the mismatch was observed more frequently in women, in our population 68% of the cases occurred in males. This disparity could be due to an insufficient size of the sample, if we consider the low prevalence observed of positive GXT with normal perfusion.

The meaning of ST segment depression in the presence of normal perfusion images is not completely clear. Some studies link it to trunkand 3-vessellesions [12-14], but other studies did not achieve establishing an angiographic relation [15-16]. In one of the few studies that have attempted to observe the angiographic correlation of the normal SPECT pattern and positive GXT, Candell-Riera et al [17], observed a majority of women with normal coronary arteries, and in the few patients with coronary lesions, the disease involved 3 vessels and/or the left main coronary artery. However, only 50% of the patients included in the study were studied by coronary angiography. He et al, reported the angiographic findings in 52 patients with positive GXT and normal SPECT, observing that when this pattern manifests in women, it is frequently associated to normal coronary arteries; but when it is observed in men, coronary lesions are more frequent; however, it is important to highlight that the study included 817 patients, from whom most were excluded from the angiographic analysis [18]. Undoubtedly, it is difficult to study the coronary anatomy in patients with normal SPECT, beyond the ST segment behavior with exercise [19-20]. For this reason, it is simpler to evaluate these patients by a clinical follow-up.

In our population, major cardiac events were not observed in none of the patients that presented ischemic changes in the ergometer test. Only 6 patients suffered minor cardiac events, with 5 of them being revascularized, and only one was treated with drugs for heart failure. These data show that beyond the reasonable doubts that may be generated by the presence of ST segment depression during ergometer test, a normal SPECT continues defining populations in low risk. The good prognosis observed, allows also to follow clinically these patients, while they evolve in an asymptomatic way and possibly study them angiographically before the appearance of angina, since some studies have reported CAD of 3 vessels in some of these patients. In our experience, only 4% of the followed patients required angiography and myocardial revascularization. Very similar data were reported by Del Val Gómez in a 2-year follow-up [21].

Cardiac SPECT is one of the most sensitive methods for the diagnosis of myocardial ischemia with an average sensibility of 88-90%. This figure indicates in an implicit way that a number of sick patients will go undetected by the method; i.e. there will always be false negatives. However, beyond these limitations proper of the method, the prognosis at one year of the patients with normal SPECT is good, regardless of the electrocardiographic changes.

 

CONCLUSIONES
In the evaluated population, the prevalence of normal SPECT studies with positive GXT by ST is very low. The prognosis in the mid term of these patients is good.

 

REFERENCES

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Publication: September 2013

 
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