This study showed that simultaneous injection of TNG and contrast angiography agent resulted in more remarkable changes in systolic and diastolic blood pressure. The incidence of coronary spasm, angina, and nausea in the intervention group was lower than the placebo group. Although this difference was not statistically significant, it was clinically noteworthy. Coronary artery spasm is one of the major complications of catheterization. Fischell, et al. investigated coronary spasm in 15 patients after angioplasty. They injected 5 patients with TNG (3 minutes after angioplasty) in 5 patients. Then, all patients underwent angiography again. Coronary artery spasms were not observed in the subsequent angiographies (2, 5, 15, and 30 minutes later) in patients who had received intracoronary TNG.9
Margolis et al. evaluated 1400 patients undergoing angioplasty in the intervention and control groups. In the intervention group (before the injection of contrast agent and through the catheter), 1 μg TNG was injected into the coronary arteries. The results suggested that the incidence of coronary spasm in subjects who had not received TNG was significantly higher than the intervention group (14% vs. 4%).10
Attention to the pathophysiology of coronary artery spasm during the catheterization is important for the treatment. Redd et al. stated that coronary artery spasm during angioplasty occurred due to the stimulation of receptors, had muscular origin, or resulted from both mechanisms. For this reason, TNG can be effective to prevent or relieve vasoconstriction caused by angioplasty.11
Chest pain is one of the other complications during coronary catheterization. Kurz et al. investigated the incidence of chest pain while placing the stent during angioplasty. In their study, the 50 patients in the intervention group received intracoronary TNG during the angioplasty. The results indicated non-significant difference in the incidence of chest pain between the two groups. However, a significant decrease was observed in the incidence of minor myocardial necrosis in the intervention group which could have been caused by better blood supply with these drugs.12
In some studies, the effect of TNG has been mentioned in patients with suspected vasospastic angina pain or in cases of risk of coronary artery spasm during angiography.13
Many previous studies have indicated the incidence of coronary artery spasm during angiography to be very rare. These studies have noted that this complication of angioplasty arose from the manipulation and further stimulation of the vessels. Since most previous studies have been performed on angioplasty, angiographic studies were rare.14
Although in the present study, the incidence of coronary artery spasm and chest pain was lower in the intervention group, due to the insignificance of the difference, using TNG during angiography to prevent side effects is not recommended. Another complication of angiography is nausea. No specific study has been found on the effect of TNG on nausea. The results of the present study indicated no significant difference in the incidence of nausea between the two groups. Since one of the common side effects of contrast agent injection is nausea5 and TNG is normally ineffective in treating nausea, the absence of a significant difference is justifiable. In this study, the incidence of arrhythmia was also similar in both groups. The origin of bradyarrhythmia may bean underlying disease or the person's susceptibility. It can be concluded that TNG had no effects in controlling the condition. The most important difference between the two groups in this study was the difference in blood pressure during angiography. The presence of statistically significant differences in the highest and lowest average systolic and diastolic blood pressure could have been the effect of TNG.As already noted, this drug is among the nitrates with vasodilatory effects. This expansion also affected the preload and after load.6
Therefore, it could be expected that TNG injections during angiography reduce blood pressure. This can be one of the important facts to be considered for recommending in patients with low blood pressure. In other words, the usage of TNG in such patients may be associated with unwanted side effects. Therefore, attention to TNG contraindications in studies is required.
In general, the results of this study indicated no significant difference in the incidence of major complications of angiography, including coronary artery spasm and chest pain, between the two groups. However, TNG reduced blood pressure. Due to the differences in the results of various studies about the incidence of coronary artery spasm and existence of a few studies on angiography, more research is required to use different doses of TNG and injection timings. Future studies are required to consider high risk patients and pain among individuals undergoing angiography and angioplasty separately. The effects of TNG on late angiographic complications and related mortality should also be evaluated in subsequent studies. In addition, reviewing the costs and spent time of using TNG and the potential complications of the drug are among the issues that need to be evaluated.