Coronary Circulation During Pacing‐induced Tachycardia

Abstract

Abstract. Coronary and systemic circulation has been studied in 10 patients with complete atrioventricular block and in 4 patients with sinus rhythm. Studies were performed during spontaneous rhythm, during pacing‐induced tachycardia (PIT) of varying frequency and during a combination of PIT and exercise. Coronary flow and myocardial oxygen uptake varied linearly with heart rate. If exercise was superimposed on PIT with unchanged pacing frequency both coronary flow and myocardial oxygen uptake increased further. The coronary flow increased mainly because of a decrease in coronary vascular resistance. The results were compared with data from a previous study in which the heart rate was increased with exercise in a group of 11 patients without signs of major heart disease. In the PIT study the increase in coronary flow and myocardial oxygen uptake for a given increment in heart rate was less than half of that found in the previous exercise study. The main explanation for this difference is probably on the one hand that wall tension decreased during PIT while it increased during exercise and on the other hand that increase in contractility was more pronounced during exercise. The same relation of coronary flow or myocardial oxygen uptake to the product of systolic pressure and heart rate (BP3 × HR) was found in both groups although the values in the PIT study were in a lower range than those in the previous exercise study. This indicates that this product is a fairly good approximation of myocardial oxygen demand over a wide range of heart rates regardless of the method used for cardio‐acceleration. It is concluded from this study that PIT is less efficient than exercise in testing the coronary vascular reserve because the stress imposed on the myocardium is low during PIT even during high heart rates.

Regulation of Coronary Blood Flow

“…12B) relative to exercise-induced increases in MVO 2 in swine (94). As depicted in Figure 12B, coronary venous PO 2 typically falls modestly as MVO 2 increases with exercise (94, 111, 213, 214, 274, 278, 280, 281, 283, 285, 293–295, 388,389,454,483,484,497,559,642,664,669,920,921,923); however, this response can vary with little/no change in swine (94, 111, 281, 663, 664, 667, 669), moderate reductions in humans (454,483,484,563), with the largest decreases typically observed in dogs (32, 274, 276, 282, 283, 285, 424, 920, 921,923–925). These reductions in PO 2 reflect slight increases in oxygen extraction that occur along with elevations in coronary blood flow in response to elevations in MVO 2 .…”

Restitution analysis of alternans using dynamic pacing and its comparison with S1S2 restitution in heptanol-treated, hypokalaemic Langendorff-perfused mouse hearts

“…Certain caution must be taken when interpreting restitution data obtained from S1S2 pacing, as a dynamic pacing protocol was shown to be more representative of the APD dynamics observed at high heart rates ( 20 , 21 ). Although it is the gold standard, dynamic pacing is often avoided in clinical situations as regular pacing at high heart rates can induce myocardial ischaemia ( 22 , 23 ). The advantage of the PES protocol is therefore safety in a clinical setting, as this does not rely on tachycardia pacing ( 19 , 21 ).…”

Cardiovascular and respiratory effects of incremental doses of dopamine and phenylephrine in the management of isoflurane-induced hypotension in cats with hypertrophic cardiomyopathy

“…29 The RPP, LVSWI, and RVSWI are crude indicators of MVo 2 . [30][31][32] Heart rate correlates well with MVo 2 ; however, coronary blood flow does not always increase proportionately with increases in HR, thereby confounding the determination of MVo 2 . Analysis of the results of the present study suggested that MVo 2 was increased with both drugs, especially when they were administered at higher doses.…”