Coronary artery distribution and variation in Rhesus monkeys
Variations in the distribution of the LAD artery in Rhesus monkeys were observed (Figure 1). As it passes toward the apex, the LAD gives off varying numbers of diagonal branches to the anterior free wall of the left ventricle. There were 4 diagonal branches (6 of 40 monkeys [15%]), 3 diagonal branches (21 of 40 monkeys [52.5%]), 2 diagonal branches (12 of 40 monkeys [30%]), and 1 diagonal branch (1 of 40 monkeys [2.5%]) variably shot from the LAD artery. Furthermore, these diagonal branches arose at different levels. The first diagonal branch shot near the origin of the LAD in 31 of 40 monkeys (77.5%). At the level around the middle of the LAD, there also arose a diagonal branch in 27 of 40 monkeys (67.5%). The end of the LAD bifurcates into two small branches occasionally (4 of 40 monkeys [10%]).
All of the animals survived until the end of the experiment. Two (out of 12) monkeys in the MI-A group, 6 (out of 12) in the MI-B group, and 4 (out of 4) monkeys in the MI-C group developed ventricle fibrillation between 25 and 40 min after the LAD ligation, but defibrillation was successful after intravenous injection of lidocaine (2 mg/kg), and/or epinephrine (2 g/kg), and/or electrical defibrillation (2 J/kg).
Effects of different ligation sites on cardiac structural changes
The MRI imaging showed that the apex, low part of the left ventricular anterior wall, and anterior interventricular septum in the LAD ligation hearts becoming thinner with irregular movement at 4 weeks after the surgery. Delayed enhancement was observed when contrast-enhanced technique was used (Figure 2). The infarct size was gradually increasing along with the elevation of ligation position at the LAD artery. In the MI-A group, a poor consistency of the infarct distribution and areas was detected. In some cases, the infarct area was spread in the low part of the anterior interventricular septum dominantly, and in other cases, the infarction was primarily located in the low part of the left ventricular anterior wall. There were also cases whose infarct area was equally distributed to the anterior interventricular septum and the left ventricular anterior wall. However, in the MI-B and MI-C groups, the location and the area of the infarction were consistent.
Histopathological examination confirmed the observation obtained from the MRI testing, the infarct areas were located in the cardiac apex, low part of the left ventricular anterior wall, and anterior interventricular septum (Figure 3). The infarct size was 23.69 ± 5.30%, 38.44 ± 3.66%, and 45.38 ± 4.06% for MI-A, MI-B, and MI-C group, respectively. In the MI-A group, the infarct area was nontransmural and scattered, survived myocardium was also found within the infarct area (Figure 3). In addition, the infarct area was disconnected. However, in the MI-B and MI-C groups, the infarct size was bigger than that in the MI-A group, and was continued and transmural (Figure 3). Variance comparison found more uniformed infarct size in the MI-B and MI-C, compared with the MI-A group (Table 1).
Table 1 Variation of infarction size in the three ligation groups
|
Sham
(n = 12)
|
MI-A
(n = 12)
|
MI-B
(n = 12)
|
MI-C
(n = 4)
|
Infarct size
|
|
|
|
|
Value (%)
|
0
|
23.69 ± 5.30
|
38.44 ± 3.66*
|
45.38 ± 4.06*†
|
CV (%)
|
0
|
22.36
|
9.53
|
8.96
|
Variance
|
0
|
28.06
|
13.42
|
16.52
|
Compared with MI-A group,* P <0.05, Compared with MI-B group, † P <0.05.
Effects of different ligation sites on cardiac functional changes
Echocardiography performed at 4 week after the LAD ligation confirmed the thinner left ventricular apex wall and decreased flexibility in cardiac movement observed from the MRI. Ventricular aneurysm was observed in most monkeys. As shown in Figure 4, standard apical 2- and 4- chamber views showed that the left-ventricular ejection fraction (EF) value was markedly reduced in monkeys with myocardial ischemic infarction. Along with the elevation of the LAD ligation level, the systolic dysfunction of the left ventricle was aggravated. In the MI-A group, abnormal cardiac movement was detected within the low part of the anterior interventricular septum or within the low part of the anterior ventricular wall. In the MI-B and MI-C groups, the extent of myocardium derangement was severer than in the MI-A group, but the location of myocardium derangement in both MI-B and MI-C groups showed a good consistency. In the MI-C group, all of the monkeys developed mural thrombus in the left ventricular apex 3 days after the operation (Figure 4). Some mural thrombus became smaller, but remained until the end of the experiment.
Coefficient of variance (CV) analysis revealed a big variance in the post-MI LVEF in the MI-A group, which was much smaller in the MI-B and MI-C groups (Table 2).
Table 2 Variation of left ventricular ejection fraction in the three ligation groups
|
Sham
(n = 12)
|
MI-A
(n = 12)
|
MI-B
(n = 12)
|
MI-C
(n = 4)
|
LVEF post-MI
(Four Chamber View)
|
|
|
|
|
Value (%)
|
75.28 ± 2.60
|
53.76 ± 9.01*
|
48.92 ± 5.97*
|
39.25 ± 7.87*
|
CV (%)
|
3.46
|
16.76
|
12.20
|
20.02
|
Variance
|
6.77
|
81.17
|
35.64
|
61.73
|
LVEF post-MI
(Two Chamber View)
|
|
|
|
|
Value (%)
|
75.48 ± 2.74
|
49.29 ± 10.32*
|
49.19 ± 3.85*
|
39.35 ± 6.00*
|
CV (%)
|
3.63
|
20.95
|
7.83
|
15.24
|
Variance
|
7.49
|
106.6
|
14.83
|
35.96
|
Compared with Sham group,* P <0.05.
The invasive ventricular pressure measurement showed that, in comparison with the sham-operated controls, the end systolic pressure (ESP), peak rate of pressure rise (Max dP/dt), and peak rate of pressure decrease (Min dP/dt) of the infarcted left ventricles were significantly decreased, but there were no significant differences among the three LAD ligation groups. The end diastolic pressure (EDP) of the left ventricle had no obvious changes (Figure 5).
The pressure-volume (PV) loop analysis revealed a right shift of the PV loop, decreased left ventricular end diastolic pressure, and a flatter slop of the end systolic pressure volume relationship (ESPVR) (Figure 5). The CV of LVESP, Max dP/dt and Min dP/dt in the MI-B and MI-C groups was smaller than that in the MI-A group (Table 3).
Table 3 Variation of left ventricular pressure parameters in the three ligation groups
|
Sham
(n = 7)
|
MI-A
(n = 6)
|
MI-B
(n = 11)
|
MI-C
(n = 4)
|
ESP
|
|
|
|
|
Value (mmHg)
|
124.57 ± 17.38
|
102.38 ± 16.22*
|
95.68 ± 13.57*
|
95.79 ± 15.60*
|
CV (%)
|
13.95
|
15.84
|
14.18
|
16.28
|
Variance
|
302.02
|
263.02
|
184.09
|
243.30
|
EDP
|
|
|
|
|
Value (mmHg)
|
10.23 ± 1.39
|
9.27 ± 4.57
|
9.94 ± 2.90
|
16.06 ± 3.03
|
CV (%)
|
13.56
|
49.35
|
29.21
|
18.86
|
Variance
|
1.93
|
20.92
|
8.43
|
9.17
|
Max dP/dt
|
|
|
|
|
Value (mmHg/s)
|
3520.47 ± 252.79
|
2633.87 ± 920.42*
|
2543.79 ± 777.77*
|
1876.12 ± 372.29*
|
CV (%)
|
7.18
|
34.95
|
30.58
|
19.84
|
Variance
|
63902.6
|
847172.75
|
604933.25
|
138600.46
|
Min dP/dt
|
|
|
|
|
Value (mmHg/s)
|
-3612.98 ± 191.34
|
-2921.23 ± 793.42*
|
-2488.11 ± 558.60*
|
-2010.53 ± 179.16*
|
CV (%)
|
-5.30
|
-27.16
|
-22.45
|
-8.9
|
Variance
|
36612.22
|
629510.27
|
312034.22
|
32097.15
|
Compared with Sham group,* P <0.05.
Alterations in ECG recordings
ST segment elevation was observed in lead II, III, and V1- V5, with the highest elevation in the V3 and V4, indicating the infarct area mainly in the anterior wall of the ventricle (Figure 6b). Eight wks after the surgery, pathological Q waves occurred (Figure 6c) and the QT interval was prolonged (Table 4). The heart rate corrected QT interval (QTc) was increased, but there were no significant differences among the three LAD ligation groups.
The R wave amplitude depression was detected in all LAD ligation groups. As shown in Figure 6d, a poor R wave progression was observed. With the increase of the ligation level, the depression of the R wave amplitude was aggravated correspondingly.
Table 4 Changes in ECG parameters in MI monkeys
|
|
Pre-ligation
1 h
|
Post-ligation
2 h
|
Post-ligation
8 wk
|
Heart rate (per min)
|
Sham
|
154 ± 16
|
148 ± 15
|
153 ± 21
|
MI-A
|
145 ± 15
|
139 ± 23
|
148 ± 14
|
MI-B
|
152 ± 19
|
135 ± 27
|
148 ± 20
|
MI-C
|
153 ± 19
|
135 ± 24
|
152 ± 22
|
P duration (ms)
|
Sham
|
56 ± 5
|
56 ± 8
|
55 ± 5
|
MI-A
|
56 ± 6
|
53 ± 7
|
62 ± 5
|
MI-B
|
54 ± 6
|
52 ± 6
|
58 ± 8
|
MI-C
|
54 ± 9
|
52 ± 6
|
62 ± 10
|
PR interval (ms)
|
Sham
|
88 ± 6
|
90 ± 7
|
87 ± 6
|
MI-A
|
90 ± 7
|
89 ± 6
|
86 ± 7
|
MI-B
|
89 ± 7
|
93 ± 8
|
88 ± 9
|
MI-C
|
89 ± 25
|
88 ± 5
|
92 ± 9
|
QRS duration (ms)
|
Sham
|
47 ± 4
|
45 ± 4
|
50 ± 3
|
MI-A
|
50 ± 3
|
52 ± 5
|
55 ± 5
|
MI-B
|
48 ± 6
|
45 ± 4
|
50 ± 7
|
MI-C
|
47 ± 3
|
44 ± 3
|
50 ± 6
|
QT interval (ms)
|
Sham
|
255 ± 29
|
246 ± 14
|
254 ± 14
|
MI-A
|
255 ± 16
|
278 ± 26*
|
272 ± 19*
|
MI-B
|
256 ± 18
|
274 ± 24*
|
274 ± 21*
|
MI-C
|
243 ± 21
|
267 ± 26*
|
273 ± 26*
|
QTc
|
Sham
|
403 ± 15
|
394 ± 15
|
400 ± 11
|
MI-A
|
394 ± 13
|
409 ± 22
|
428 ± 37*
|
MI-B
|
412 ± 24
|
401 ± 22
|
431 ± 26*
|
MI-C
|
398 ± 19
|
395 ± 17
|
434 ± 26*
|
Compared to sham control, * P<0.05
MI = myocardial infarction
Variations in blood testing
Lactate dehydrogenase (LDH), cardiac troponin I (cTnI), creatine kinase (CK), and myoglobin (Mb) were increased significantly and proportionally to the increase of the LAD ligation position. The level of creatine kinase-MB (CK-MB) was significantly increased in the late phase of myocardial infarction (Table 5).
Table 5 Changes in cardiac injury markers in MI monkeys
|
|
Pre-ligation
1 h
|
Post-ligation
2 h
|
Post-ligation
24 h
|
Post-ligation
8 wk
|
LDH (U/L)
|
Sham
|
226 ± 63
|
225 ± 35
|
230 ± 42
|
228 ± 32
|
MI-A
|
222 ± 48
|
375 ± 88*
|
1332 ± 93*
|
240 ± 47
|
MI-B
|
233 ± 62
|
293 ± 67*
|
1425 ± 143*
|
238 ± 55
|
MI-C
|
220 ± 28
|
433 ± 116*
|
2345 ± 384*
|
241 ± 44
|
cTnI (ug/L)
|
Sham
|
<0.01
|
<0.01
|
<0.01
|
<0.01
|
MI-A
|
<0.01
|
1.5 ± 0.4*
|
12.3 ± 4.2*
|
<0.01
|
MI-B
|
<0.01
|
1.7 ± 0.9*
|
17.3 ± 7.2*
|
<0.01
|
MI-C
|
<0.01
|
2.6 ± 1.8*
|
24.6 ± 9.2*
|
<0.01
|
CK-MB (U/L)
|
Sham
|
113 ± 40
|
111 ± 29
|
120 ± 48
|
115 ± 41
|
MI-A
|
102 ± 24
|
144 ± 27
|
232 ± 82*
|
106 ± 40
|
MI-B
|
126 ± 27
|
143 ± 71
|
264 ± 74*
|
108 ± 73
|
MI-C
|
128 ± 33
|
183 ± 74*
|
>300*
|
115 ± 66
|
CK (U/L)
|
Sham
|
179 ± 23
|
187 ± 71
|
183 ± 42
|
181 ± 74
|
MI-A
|
186 ± 7
|
1237 ± 385*
|
1432 ± 249*
|
171 ± 126
|
MI-B
|
181 ± 31
|
1457 ± 328*
|
1721 ± 381*
|
178 ± 112
|
MI-C
|
183 ± 34
|
1513 ± 480*
|
1858 ± 329*
|
179 ± 113
|
Mb (μg/L)
|
Sham
|
109 ± 46
|
107 ± 56
|
113 ± 65
|
110 ± 32
|
MI-A
|
96 ± 25
|
266 ± 120*
|
131 ± 30
|
108 ± 24
|
MI-B
|
105 ± 49
|
247 ± 46*
|
148 ± 51
|
116 ± 38
|
MI-C
|
115 ± 23
|
347 ± 106*
|
183 ± 64*
|
114 ± 49
|
Compared to sham control, *P<0.05
MI = myocardial infarction