The evidence based clinical literature reveals the difficulties in diagnosing Myocardial Infarction (MI) concomitantly with pre-existing left bundle branch block (LBBB) with the application of 12 lead ECG in the pre-hospital environment (Surawicz and Knilans, 2008). Indeed, the T waves and baseline ST segments incongruently displaced in negative direction in cases of LBBB as evident through the ECG findings. These abnormal variations in ECG findings tend to override the actual ECG results in relation to MI manifestations, thereby challenging the confirmation of MI with the ECG intervention. However, the moving ST segments revealed through the serial ECGs during ischemic episodes in context to the demand characteristics and dynamic supply. Indeed, the acute phase of LBBB is mostly pathological and represents the manifestation of MI. However, the occurrence of LBBB is not common with anterior MI and in case this happens, the prognostic outcomes relate to the conduction disturbances and other bad prognostic manifestations (Chugh, 2012, p. 257). The probability of MI with LBBB is ruled out with the utilization of Sgarbossa criteria in clinical medicine. The research literature further reveals LBBB as chronic ECG outcome with questionable relationship with cardiovascular ischemia. The acute changes in context to MI manifestations are masked in the ECG findings, thereby challenging the medical decision for executing primary percutaneous coronary intervention (PPCI) following the clinical scenario. Hence, the application of Sgarbossa criteria facilitates the confirmation of MI manifestations through ECG findings. Indeed, this relatively easy criteria needs to be taught to the paramedical professionals working across healthcare facilities to generate precision in medical decision making in context to accurately diagnosing MI with pre-existing LBBB.
The 58 years old female patient reported to the clinical setting with the complaint of non specific acute central chest pain radiating to the left arm, with pain score – 6 and pertaining to 30 minutes duration. The patient also experienced slight nausea without any reported vomiting. The patient did not have any personal history of cardiac disease; however, she reportedly appeared to be mild smoker and social drinker. The patient was overweight with elevated BMI, thereby predisposed to increased risk of cardiovascular disease. The physical examination of the patient revealed clear respiratory passage and normal respiratory rate and breath sounds with appropriate oxygen saturation level. However, the heart rate appeared irregular and blood pressure and blood glucose level reported to be within normal limits. Indeed, chest pain with irregular heart beat occurring in an acute episode may represent patterns of arrhythmia as evidenced by the clinical literature. Macfarlane, et al. (2011) reveal the occurrence of patterns of acute chest pain in cases of right bundle branch block, coronary artery occlusion and myocardial ischemia. Indeed, the episodes of acute central chest pain with pre-existing LBBB indicate the probability of an ischemic episode warranting confirmation with the utilization of Sgarbossa ECG criteria (Brady and Truwit, 2009). This criterion claims 90 % specificity in tracking the patterns of acute MI in patients reporting with acute chest pain and preexisting LBBB. Parrillo and Dellinger (2014, p. 474) advocate the contention of adverse clinical prognosis for patients with patterns of acute MI and LBBB, and reporting the clinical setting with acute chest pain manifestation. Indeed, the ECG findings pertaining to ST segment depression evidenced in precordial leads predispose the patients of acute inferior STEMI toward developing larger ischemic episodes, complications following MI and increased mortality rate as compared to the patients with lack of precordial ST segment depression.
Patient’s case in context to the relevant research literature
The female patient with 58 years of age reported to the clinical facility with intensely radiating acute chest pain and nausea. The 12 lead ECG findings of the patient reveal the ST elevation of greater than 1 mm and positive QRS complex in context to the concordance in the ST shifts. Jayasinghe (2012, p. 81) discusses the contention of acute MI diagnosis in relation to the reported patterns of concordant ST deviation. However, the features of LBBB attribute to the depression in ST segment (in V-5 and V-6) and inversion in T wave. The discordant ST segment elevation is reported between V-1, V-2 and V-3 in cases of LBBB as evidenced by the clinical literature. Therefore, any ST segment elevation in relation to the convexity in morphology is indicative of acute anteroseptal myocardial infarction. The patient’s nil cardiac history reveals that LBBB is newly diagnosed and of acute nature. The prevalence of LBBB increases with age a evidenced by clinical studies (Rich and Shen, 2012). Indeed, the appearance of acute chest pain with newly diagnosed LBBB is highly indicative of an acute episode of myocardial infarction. The active comparison of patient’s present ECGs with past ECG findings warranted to capture the age of LBBB in context to identifying MI among the patients with cardiovascular symptoms. Furthermore, the ST depression of more than 1 mm reported between V-1 – V-3 reveals ST shift concordance in the ECG findings. Baltazar (2009, p. 371) describes the patterns of depression in ST segment (between V-1 until V-3) in context to the diagnosis of posterolateral MI. Indeed, the relevance of these findings attribute to the reciprocal orientation of these leads against the posterolateral wall. This V-1 – V-3 ST depression may erroneously indicate ischemia of anterolateral wall of left ventricle despite the active probability of transmural MI. Interestingly, the acute lateral MI reported with patterns of ST elevation in V-5 and V-6 with or without depression in ST segment (between V-1 to V-3) . The right sided precordial captured in the clinical setting revealed ST alteration of greater than 1 mm in the lead, thereby indicating myocardial infarction in context to the clinical findings. Baltazar (2009a, p. 372) advocate the significance of right sided precordial lead (RSPL) in capturing the patterns of acute MI. Indeed, the RSPL requires immediate recording for the patients with reported chest pain (with LBBB) as the ECG changes revealing patterns of MI may resolve within initial few hours following the onset of clinical symptoms. Precordial QRS duration of greater than 160 m sec, if observed with LBBB may indicate the patterns of ventricular tachycardia in the affected patients (Issa, Miller and Zipes, 2009, p. 395).
The relevance of Morphine in context to initiating analgesia
The patient received 10mg Morphine in context to treating the manifestation of her chest pain in the clinical setting. Hodgson and Kizior (2014, p. 890) reveal the pharmacokinetics of morphine in terms of reducing moderate to severe acute pain episode. This drug is administered through parenteral route and the onset of desirable outcomes begins within a span of 5-10 minutes following the administration. The drug is well absorbed and widely distributed with protein binding of 10%. However, the half life of morphine corresponds to 4– 6 hours and excreted through urine within 9-11 hours of its administration. Ries, et al. (2009, p. 120) reveal the oral bioavailability range of morphine between 60 % – 87 % in 45% protein bound state. However, the metabolites of morphine include oxycodone and noroxycodone with moderate to potent analgesic properties. Indeed, oxycodone shares similar properties with morphine in relation to extended half-life and enhanced bioavailability; however, the metabolism of oxycodone is influenced by CYP2D6 unlike the glucuronidation mechanism of morphine. Morphine is processed in liver and its clearance consumes time because of oral and enterohepatic metabolism.
The relevance of GTN in relation to clinical scenario
The patient also received GTN (Glyceryl Trinitrate) 500mg through sublingual route in context to the cardiovascular origin of her chest pain. Indeed, GTN is the drug of choice in treating or prophylactically managing episodes of angina, heart failure and acute MI. Glyceryl Trinitrate is available as a slow release formulation and undergoes rapid metabolism in liver and converted to dinitrates with 10% of biological activity in comparison to the parent drug (Bryant and Knights, 2011, p. 472). The standard dosages of GTN sublingual tablets correspond to 300 – 600 mcg that may require repetition within each 5 minutes in context to administering 1200 – 1800 mcg following the clinical condition.
The clinical protocol for oxygen administration
The oxygen therapy was not administered to the patient as pulse oximetry finding revealed her oxygen saturation level accounting to 99%. The evidence based practice prescribes clinical norms for oxygen administration to the overweight female patients at increased cardiovascular risk (Yoost and Crawford, 2015, p. 966). Indeed, the oxygen therapy is warranted only for patients with oxygen saturation levels attributing to less than 90%. Janice, et al. (2013, pp. 766-767) discuss the relevance of oxygen therapy in enhancing the supply of oxygen to myocardium for reducing the episodes of chest pain. Furthermore, the therapeutic efficacy of oxygen therapy is evaluated by observing respiratory patterns among the affected patients.
The relevance of PPCI in comparison to the thrombolytic therapy
The research studies reveal the difficulties in performing primary angioplasty (PPCI) in patients that are simultaneously affected with acute MI and LBBB. Handler and Cleman (2006, p. 39) describe the relevance of PPCI reperfusion therapy including balloon angioplasty and subsequent stenting procedure in the absence of concomitant thrombolytic intervention for treating STEMI. Indeed, the PPCI therapy provides added advantages as compared to thrombolytic intervention in terms of reducing mortality rates and enhancing outcomes in context to the clinical scenario. Handler and Cleman (2006, p. 20) discuss the significance of PPCI reperfusion intervention in improving the outcomes of STEMI. However, PPCI therapy is not recommended in cardiovascular complexities, where LBBB is associated with probability of MI in context to the clinical manifestations. The evidence based clinical literature reveals the 98% specificity of Sgarbossa criteria in acquiring positive predictions for MI patterns in patients affected with LBBB. Indeed, with increased specificity in acquiring STEMI diagnosis, the clinical goals can be achieved accordingly. However, the reduced sensitivity in clinical findings through Sgarbossa criteria leads to considerable delays in administering reperfusion therapy to the patients suspected with STEMI due to the proportionate delays in ruling out patterns of AMI (Grossman and Rosen, 2011, p. 323).
The Sgarbossa criteria
The evidence based clinical literature advocates the contention of the complexities in precisely acquiring the diagnosis of MI through ECG findings in known cases of LBBB. The LBBB condition influences the ECG outcomes in context to discordantly altering the T waves and baseline ST segments, thereby creating difficulties in diagnosing MI. Furthermore, the newly diagnosed rather than chronic LBBB may prove to be the outcome of MI with the application of Sgarbossa ECG criteria. The score of 5 obtained through this criterion attributes to ST elevation of greater than 1 mm in association with the positive QRS complex. However, the score – 3 corresponds to ST depression of greater than 1 mm in V-1 – V-3 leads. The score 2 is obtained if ST elevation reported to be greater than 5 mm in association with negative QRS complex. The clinical studies executed by Mayo Clinic reveal the 100 % specificity and 14% sensitivity of Sgarbossa score – 5 in diagnosing acute myocardial infarction (Mattu & Mehra, 2012). The decreased sensitivity of the Sgarbossa criteria challenges its routine utilization in diagnosing the patterns of acute MI. The clinical studies described by Dries, et al. (2013, p. 28) indicate the independent predictive capacity of LBBB diagnosis in identifying the predisposition to cardiac comorbidities among the patients affected simultaneously with MI and evaluated through Sgarbossa criteria. Indeed, the patient in the presented clinical scenario could have experienced increased death risk in the absence of active implementation of Sgarbossa ECG criteria in identifying acute MI with LBBB. The evidence based clinical literature contends the utilization of Sgarbossa criteria by paramedical professionals for potentially assisting physicians in diagnosing the patterns of acute MI with pre-existing LBBB. Rowe, et al. (2009) conclude that two or three Sgarbossa parameters are sufficient to rule out acute AMI following the clinical scenario; however, reduced Sgarbossa scores do not entirely exclude the possibility of acute MI in the clinical context of LBBB.
Indeed, the patterns of acute coronary syndrome, MI and LBBB prove to be the significant diagnostic challenges for the treating physician. The evidence based clinical literature recommends reperfusion intervention for patients with LBBB; however the probability of acute MI in these patients poses challenges in terms of administering fibrinolytic therapy and cardiac catheterization in the absence of definitive diagnosis. Therefore, the selection of patients for appropriate reperfusion or thrombolytic therapy requires precise clinical decision making in terms of attaining appropriate diagnosis (pertaining to LBBB vs. MI) through the active utilization of Sgarbossa criteria. Indeed, the accomplishment of three Sgarobossa parameters attribute to 78% sensitivity and 90 % specificity in confirming or ruling out AMI in the clinical setting of LBBB. The Sgarobossa outcomes on electrocardiographic findings have the capacity of identifying the individuals with increased predisposition to STEMI and its potential manifestations and therefore, this criterion is highly warranted in context to its potential incorporation in determining the patterns of acute MI with pre-existing LBBB.
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