Effects of experimental pulmonary embolism on electrocardiographic parameters, blood pressure, exercise tolerance and cardiac morphometry in the domestic dog (canis familiaris)
Onyango, Edward Michieka
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Thirty 8 inch long polyvinyl chloride threads were used to experimentally induce pulmonary embolism in mongrel dogs. Electrocardiographic parameters in the six limb leads and blood pressures in the pulmonary artery, right ventricle and right atrium were measured before and also during a 35 day period following insertion of threads in the pulmonary artery. Exercise tolerance was assessed before and 33 days following thread insertion. At the end of the experimental period the dogs were euthanised and morphometry of their hearts studied. Similarly, morphometry of hearts from control dogs was also studied. The amplitude and frequency of Q wave in lead I, recorded during the 35 days following thread insertion was significantly lower than the baseline value. The amplitude of R wave in lead II on days 21-35 and of S wave in lead aVR on days 7-35 after thread insertion was significantly lower than the baseline value. The S wave in lead I was only present after thread insertion. The duration of the QRS complex was significantly longer than the baseline value on the 14th day after thread insertion. Five out of twelve (41.6%) dogs showed right axis deviation following thread insertion. The amplitude of T wave in leads II and III on days 2 and 3, and of aVF on days 1-3 was significantly higher than the respective baseline values following thread insertion. In leads aVR and aVL the values were significantly lower than the respective baseline value on day 3 after thread insertion. In addition in lead aVL, T wave amplitude was significantly higher than the baseline value on day 7 after thread insertion. The x following arrhythmias were noted during the 35 days following thread insertion: supraventricular premature beats, first degree heart block, ventricular premature beats, junctional tachycardia, ventricular tachycardia, second degree heart block and sinus tachycardia. Immediately following thread insertion the pulmonary arterial and right ventricular blood pressures rose significantly. Thereafter the pressures dropped, but remained at levels which were still higher though not all were significantly different from respective baseline values. Right atrial pressure remained unchanged throughout the experimental period. The hearts of experimental dogs at the end of the 35 day period did not show any significant change in weight nor in right or left ventricular wall size when compared to the controls. Exercise tolerance remained unchanged throughout the experimental period. Mean rectal temperature, pulse and respiration rates during the experimental period remained within the normal range. It is concluded that for Kenya mongrel dogs whose baseline electrocardiogram has been established in the present study and also for any other dog whose baseline electrocardiogram is known, a diagnosis of pulmonary embolism could be made and the progression of the embolism followed by examining changes in the QRS complex and the T wave. Also pulmonary hypertension can be achieved using pulmonary emboli in the form of polyvinyl chloride threads.